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Tintinalli's Emergency Medicine: A
Comprehensive Study Guide >
Bites and Stings
Aaron B. Schneir
Bites and Stings: Introduction
The phylum Arthropoda is the largest division of the animal kingdom. The phylum includes insects (bees, wasps,
hornets, flies, mosquitoes, bedbugs, fire ants, caterpillars, fleas), arachnids (spiders, scorpions, chiggers, ticks),
and crustaceans (shrimp, lobsters, crabs). Venomous bites and stings from arthropods are a significant worldwide
problem.1 In the U.S., the American Association of Poison Control Centers reported almost 50,000 cases of
exposures to arthropods in 2008.2 Some of these were listed as resulting in major or severe reactions, including
severe pain, neurotoxicity, or other signs and symptoms. Fatalities among these exposures are rarely reported to
poison centers and usually result from allergic reactions to Hymenoptera stings. Clearly, these numbers are the tip
of the iceberg. Toxic reactions to multiple stings by members of the order Hymenoptera and severe systemic
allergic reactions to one or more stings or bites of other insects, such as deerflies, blackflies, horseflies, and
kissing bugs, can all present as emergency, life-threatening situations (Table 205-1).3 Other arthropod bites and
envenomations merit review either because they cause specific organ system toxicity or because they can result in
transmission of infectious disease. This chapter discusses the more common and serious arthropod bites and
envenomations encountered by emergency physicians.
Table 205-1 Harmful Arthropods of the U.S.
Class and Order
Common Name
Bite
Sting
Hexapoda (Insecta)
Hymenoptera
Bumblebees
x
Sweat bees
x
Honeybees
x
Wasps
x
Hornets
x
Yellow jackets
x
Fire ants
x
Harvester ants
x
Mosquitoes
x
Deerflies
x
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Diptera
Hemiptera
Lepidoptera
Horseflies
x
Stable flies
x
Blackflies
x
Biting midges
x
Bedbugs
x
Kissing bugs
x
Puss caterpillars
x
Brown tail caterpillars
x
Buck moth caterpillars
x
Siphonaptera
Fleas
x
Anoplura
Lice
x
Black widow spider
x
Brown recluse spider
x
Hobo spider
x
Tarantula
x
Chiggers (mite larvae)
x
Ticks
x
Arachnida
Araneida
Acarina
Scorpionida
Scorpions
x
Reproduced with permission from Frazier CA: Insect Allergy. St. Louis, WH
Green, 1987, p. 421.
Hymenoptera (Wasps, Bees, and Ants)
The Hymenoptera are the most important venomous insects known to humans, and more fatalities result from
stings by these insects than by stings or bites by any other arthropod. There are three major subgroups or
superfamilies of medical importance: (1) Apidae, which includes the honeybee and bumblebee; (2) Vespidae, which
includes yellow jackets, hornets, and wasps; and (3) Formicidae, or ants (Figure 205-1).
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FIGURE 205-1.
Representative venomous Hymenoptera. A. Hornet (Vespula maculata). B. Wasp (Chlorion ichneumerea). C. Yellow
jacket (Vespula maculiforma). D. Honeybee (Apis mellifera). E. Fire ant (Solenopsis invicta). (Reproduced with
permission from Merck, Sharp & Dohme, Division of Merck & Co., Inc.)
Bees and Wasps (Apidae and Vespidae)
Apids, such as honeybees and bumblebees, are usually docile, stinging only when provoked. A female bee is
capable of stinging only once (male bees have no stinger), because its stinger has multiple barbs that cause the
sting apparatus to detach from the bee’s body, which leads to evisceration and eventual death.
Africanized honeybees, or so-called killer bees, are now found in most of the southern and warmer regions of the
U.S. extending from coast to coast. These bees are hybrids of African bees that escaped from laboratories in Brazil
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during the 1950s and have successfully spread northward along the coasts and temperate regions of the
continent. Their venom is no more toxic than that of their American counterpart, but Africanized hybrid honeybees
are more aggressive, and a hive can respond to a perceived threat with >10 times the number of bees that respond
from a hive of typical North American bees. An attack from Africanized bees can lead to massive stinging resulting
in multisystem damage and death from severe venom toxicity.4,5
Most of the allergic reactions reported each year due to Hymenoptera occur from vespid (wasp, hornet, and yellow
jacket) stings. These arthropods nest in the ground, in trees, or in walls; have volatile tempers; and may be
disturbed by work taking place around the nest. As with bees, only the females have adapted a stinger from the
ovipositor on the posterior aspect of the abdomen. Although vespids also possess barbed stingers, they have the
ability to withdraw their stingers from the victim, which permits multiple stings.
Venom
Hymenoptera venom contains several components.6 Although histamine is one of those components and was
once thought to be responsible for most of the reactions observed following envenomation, other substances have
now been recognized as more important. Melittin, a known membrane-active polypeptide that can cause
degranulation of basophils and mast cells, constitutes >50% of the dry weight of bee venom. Because all
Hymenoptera share many of these components, cross-sensitization may occur in individuals allergic to one
species. Yellow jacket venom is perhaps the most potent sensitizer.
Clinical Features
The most common response to Hymenoptera venom is pain, slight erythema, edema, and pruritus at the sting site.
In addition to this response, more significant reactions may occur.7
Local Reaction
A local reaction consists of an urticarial lesion contiguous with the sting site. Although there are no systemic signs
or symptoms, a severe local reaction may involve one or more neighboring joints. A local reaction occurring in the
mouth or throat can produce airway obstruction. Stings around the eye or on the lid may result in the development
of an anterior capsule cataract, atrophy of the iris, lens abscess, perforation of the globe, glaucoma, or refractive
changes. When local reactions become increasingly severe, the likelihood of future systemic reactions appears to
increase, and if skin test results are positive, immunotherapy may be warranted.
Toxic Reaction
When there is a history of multiple stings, such as in an Africanized bee attack, a systemic toxic reaction from
venom may occur. Symptoms of a toxic reaction may resemble anaphylaxis, but there is generally a greater
frequency of nausea, vomiting, and diarrhea. Light-headedness and syncope are common. There also may be
headache, fever, drowsiness, involuntary muscle spasms, edema without urticaria, and, occasionally, convulsions.
Urticaria and bronchospasm do not need to be present, although respiratory insufficiency and arrest may occur.
Renal and hepatic failure and disseminated intravascular coagulation can result from massive bee stings. Creatine
phosphokinase concentrations can reach 100,000 IU/L or more in cases in which rhabdomyolysis occurs from
direct venom toxicity.5 Toxic reactions are believed to occur due to a direct multisystem effect of the venom.
Symptoms usually subside within 48 hours but may last for several days in severe cases, and some effects, such
as rhabdomyolysis, can be delayed. We are now recommending hospital admission/observation for victims
with >100 stings, for those with substantial comorbidities, and for those at extremes of age.
Anaphylactic Reaction
A generalized systemic allergic or anaphylactic reaction, whether in response to a single sting or multiple stings,
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may range from mild to fatal, and death can occur within minutes. The majority of such reactions develop within
the first 15 minutes, and nearly all occur within 6 hours. There is no correlation between systemic reaction and the
number of stings. In general, the shorter the interval between the sting and the onset of symptoms, the more
severe is the reaction. Fatalities that occur within the first hour after the sting usually result from airway obstruction
or hypotension. Initial symptoms generally consist of itching eyes, facial flushing, generalized urticaria, and dry
cough. Symptoms may intensify rapidly, with chest or throat constriction, wheezing, dyspnea, cyanosis, abdominal
cramps, diarrhea, nausea, vomiting, vertigo, chills and fever, stridor, shock, syncope, involuntary bowel or bladder
action, and bloody, frothy sputum. Initially mild symptoms may progress swiftly to shock. Signs and symptoms
may recur 8 to 12 hours after the initial reaction.
Generalized systemic allergic reactions to Hymenoptera venom are thought to be immunoglobulin E mediated.
When an individual predisposed to allergy to bees is stung, there is usually an increase in the production of
immunoglobulin E antibodies, which become attached to the mast cells and basophils. This sensitizes the
individual so that a subsequent sting may result in an antigen-antibody interaction releasing pharmacologically
active mediators that cause tissue damage and systemic symptoms. (See Chapter 27, Anaphylaxis, Acute Allergic
Reactions, and Angioedema.)
Delayed Reaction
A delayed reaction, appearing 5 to 14 days after a sting, consists of serum sickness–like signs and symptoms of
fever, malaise, headache, urticaria, lymphadenopathy, and polyarthritis.8 Frequently, the patient has forgotten
about the encounter and is puzzled by the sudden appearance of symptoms. This reaction is believed to be
immune complex mediated.
Unusual Reactions
Infrequently, a reaction to Hymenoptera venom produces neurologic, cardiovascular, and urologic symptoms, with
signs of encephalopathy, neuritis, vasculitis, and nephrosis. A case of Guillain-Barré syndrome has been reported
as a possible consequence of a Hymenoptera sting.
Identification of the offending insect can be difficult, except for the honeybee, which predictably leaves its stinger
with venom sac attached in the lesion. In general, definitive identification is unnecessary, because signs and
symptoms of envenomation are similar for all species of Hymenoptera. If edema persists at the sting site, then
secondary infection, such as cellulitis, should be considered. Severe local reactions on the foot or ankle can be
misdiagnosed as gout if the insect sting is not visible.
Treatment
If the bee stinger is present in the wound, it should be removed. Although conventional teaching suggested
scraping the stinger out to avoid squeezing remaining venom from the retained venom gland into the tissues,
involuntary muscle contraction of the gland continues after evisceration, and the venom contents are quickly
exhausted. Immediate removal is the important principle, and the method of removal is irrelevant. The sting site
should be washed thoroughly with soap and water to minimize the possibility of infection. For local reactions,
intermittent application of ice packs at the site diminishes swelling and delays the absorption of venom while
limiting edema. Oral antihistamines and analgesics may limit discomfort and pruritus. NSAIDs can be effective in
relieving pain. Standard doses of opioid analgesics also can be administered. If edema is significant, elevation and
rest of the affected limb should limit swelling unless secondary infection develops, in which case antibiotics are
necessary. In local tissue reactions, there is often significant inflammatory erythema and swelling, which make it
difficult to distinguish from infection. As a general rule, infection is uncommon.
Although the initial signs and symptoms of a systemic reaction may be mild, the victim’s condition can deteriorate
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rapidly in a matter of minutes. Treatment begins similarly to that for anaphylaxis (see Chapter 27, Anaphylaxis,
Acute Allergic Reactions, and Angioedema), and the most important agent to administer is epinephrine, 0.3 to 0.5
milligram (0.3 to 0.5 mL of 1:1000 concentration) in adults and 0.01 milligram/kg in children (never more than 0.3
milligram). It should be injected IM and the injection site massaged to hasten absorption. To avoid mishaps in
dosing, many EDs now stock adult and pediatric EpiPens, which provide the standard adult or pediatric
dose (EpiPen, 0.3 milligram epinephrine; EpiPen-Jr, 0.15 milligram epinephrine). The patient should then be
observed for several hours to ensure that symptoms do not intensify or relapse. Parenteral administration of
standard antihistamines (diphenhydramine, 25 to 50 milligrams IV, IM, or PO) and histamine-2 receptor antagonists
(ranitidine, 50 milligrams IV) is recommended. Although there is little direct support for adding steroids
(methylprednisolone, 125 milligrams IV, prednisone, 60 milligrams PO), their administration may limit ongoing
urticaria and edema, blunt current symptoms, and potentiate the effects of other measures. Bronchospasm is
treated with β agonist nebulization. Hypotension may require massive crystalloid infusion, and central venous
pressure monitoring may be helpful in these patients. Persistent hypotension after massive volume replacement
may require dopamine. If dopamine administration is ineffective, an IV infusion of epinephrine can be used. A
patient who experiences a severe systemic reaction should be admitted and monitored for potential cardiac,
bleeding, renal, or neurologic complications. Antivenoms have been studied for the treatment of mass bee attacks,
but are not yet commercially available.9
Long-Term Management and Preventive Care
Results of skin tests and radioallergosorbent tests are not fully reliable for determining which patients are at risk for
systemic reaction during future encounters with Hymenoptera (Table 205-2), but should be coupled with
information from the clinical history.10 Patients with negative test results may have been sensitized by the skin
tests themselves. Every patient who has had a systemic reaction should be provided with an insect sting kit
containing premeasured epinephrine and should be carefully instructed in its use. The physician should stress that
the patient must inject the epinephrine at the first sign of a systemic reaction. Physicians should also advise their
patients who are allergic to insects to wear identification (e.g., medical alert tags) describing their severe allergy.
They should also be advised to follow up with an allergist.
Table 205-2 Long-Term Management for Patients with Reactions to Hymenoptera Stings
Type of Reaction
Risk of Systemic
Reaction on
Subsequent
Stings
Perform
Skin
Testing?
Never stung
Minimal
No
None
Minor local reaction: immediate
pain, swelling, and itching at
sting site, resolves in 1 d
Minimal
No
None
Extensive local reaction:
swelling develops 24–48 h after
sting and resolves in 3–7 d
<10%
No
Epinephrine
syringe
Results
of Skin
Testing
Recommended
Treatment
Local reaction
Systemic reaction
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Adult (urticaria, angioedema,
anaphylaxis)
Child (urticaria and mild
angioedema)
High
Low
Moderate
Yes
Yes
Yes
+
Venom
immunotherapy
plus
epinephrine
syringe
–
Epinephrine
syringe
+
Venom
immunotherapy
or epinephrine
syringe
–
Epinephrine
syringe
+
Venom
immunotherapy
plus
epinephrine
syringe
–
Epinephrine
syringe
Child (anaphylaxis)
Ants
There are five known species of fire ants (Solenopsis) in the U.S.: the native species S. aurea, S. geminata, and S.
xyloni, and at least two imported species, S. invicta and S. richteri. These two imported species entered the U.S.
through Mobile, Alabama, in the 1930s, have now become well established throughout the Gulf Coast states, and
are spreading throughout the southwest.11 Fire ants inhabit loose dirt and breed 9 to 10 months of the year. One
mature nest can produce 200,000 ants during a 3-year period, which accounts for the rapid spread of this
arthropod. The venom of the fire ant is almost entirely an insoluble alkaloid. There is potential cross-reactivity
between the venoms of fire ants and those of other Hymenoptera, and individual stings may produce systemic
toxicity in sensitized individuals.
Fire ants are characterized by their tendency to swarm when provoked, and they may attack in great numbers. Fire
ants in a swarm most often position themselves on their victim and sting simultaneously in response to an alarm
pheromone released by one or several individuals. Immobilized or elderly patients can become rapidly covered by
swarms, which results in severe stings or death.12 Each sting usually results in a papule that becomes a sterile
pustule in 6 to 24 hours (Figure 205-2). Localized necrosis, scarring, and secondary infection can result. Rarely, a
systemic reaction manifested by urticaria and angioedema can occur. Fatalities and other severe reactions have
been reported to occur rapidly following single stings from ants, but most of these patients had a history of prior
venom allergy, many had prior cardiopulmonary disease, and none carried injectable
epinephrine.13,14 Rhabdomyolysis and renal failure have also been reported after massive fire ant stings.15
FIGURE 205-2.
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Fire ant bites. These bites on the anterior knee occurred when the patient knelt on a fire ant mound. The bites are 3
days old. The initial sterile pustules have begun to crust over. (Photograph by Alan Storrow, MD. Reproduced with
permission from Knoop KJ, Stack LB, Storrow AB, Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009
by McGraw-Hill, Inc., New York.)
Studies estimate a hypersensitivity to fire ant venom in 16% of the general population, with significant crossover
with those sensitized to the stings of other Hymenoptera. Treatment of fire ant stings consists of local wound
care.12 If there is evidence of systemic reaction, the usual treatment for anaphylaxis is indicated. Desensitization
may be necessary in patients exhibiting potentially life-threatening reactions to these arthropods. The wearing of
socks or cotton tights seems to provide more protection from fire ant stings than the use of insect repellants.16
Spiders (Araneae)
Although nearly 40,000 species of spiders have been described worldwide, medically significant envenomations
have been described in only a few dozen (Tables 205-3 and 205-4). Spiders are carnivores, and venom probably
evolved for paralyzing prey. The vast majority of spiders pose little harm to humans because their venom-injecting
fangs are too small to penetrate human skin, the amount of venom injected is too little to produce toxicity, or the
venom itself has little effect on mammalian cells. Even if a reaction is elicited, it is often local, and systemic toxicity
is confined to a few specific species (Table 205-4).
Table 205-3 Medically Important Spiders and Geographic Distribution
Genus
Species
Common Name
Distribution
North America, South America,
Africa, Mediterranean countries
L. reclusa
True brown recluse
spider
North America (central and
southeast U.S.)
L. arizonica
Arizona brown spider
North America (southwest U.S.)
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Loxosceles
L. rufescens
L. laeta
Worldwide
Corner spider
South America, North America
L. spinulosa
South Africa
L. intermedia
Brazil
L. gaucho
Brazil
L. parrami
Violin spider
South Africa
Europe, North America
Tegenaria
T. agrestis
Hobo or northwestern
brown spider
Europe, Asia (west central):
native
North America (Pacific
Northwest): introduced
Worldwide
L. mactans
Black widow spider
North America
L. bishopi
Red-legged spider
North America
L. variolus
Latrodectus
North America
L. hasselti
Redback spider
Australia, New Zealand, Asia
(southern)
L. katipo
Katipo spider
New Zealand
L. hesperus
Western black widow
spider
North America
L.
tredecimguttatus
Mediterranean countries
L. pallidus
Mediterranean countries,
Middle East, Russia (south)
L. indistinctus
Black button spider
Africa
L. geometricus
Brown button spider
Worldwide
L. rhodesiensis
Brown button spider
South Africa
South America
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Phoneutria
P. nigriventer
Brazilian armed
spider
Brazil, Paraguay, Argentina,
Uruguay
Australia
A. robustus
Sydney funnel-web
spider
Australia (east)
H. formidabilis
Northern funnel-web
spider
Australia (east)
H. versutus
Australian Blue
Mountains funnelweb spider
Australia (east)
Atrax/Hadronyche
H. infensus
Australia (east)
H. cereberus
Australia (southeast)
Worldwide
Cheiracanthium
C. inclusum
North America
C. mildei
Europe, eastern and central
U.S.
C. diversum
Australia, Pacific Islands,
Hawaii
C. punctorium
Europe
C. longimanus
Australia
C. mordax
Australia
C. japonicum
Japan, China
C. lawrencei
(furculatum)
Sac spider
Africa
Table 205-4 Medically Important Spider Bites: Local Reaction and Systemic Signs
Genus
Local Reaction
Systemic Signs
Bite is initially painless.
Systemic effects are rare, appear
more often in children, and typically
occur 24 to 72 h after the bite.
Most common manifestation is a
mild, firm erythematous lesion that
heals with little or no scar over
several days to weeks.
Nausea, vomiting, fever, chills,
arthralgias, hemolysis,
thrombocytopenia, hemoglobinuria,
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Loxosceles
Occasionally mild to severe pain
occurs several hours after the bite
followed by erythema and blister
formation within 24 h.
and renal failure may be seen.
Disseminated intravascular
coagulation and death are rare
complications.
Necrotic lesion develops over the
next 3 to 4 d, with eschar formation
by the end of the first week.
Tegenaria
Initial bite is often painless.
Headache is the most common
systemic symptom.
Induration may initially occur with
surrounding erythema.
Nausea, vomiting, and fatigue can
also occur.
Blistering, rupture, and necrosis
follow.
Aplastic anemia and death are rare
complications.
Healing may take as long as 45 d,
and permanent scarring may result.
Latrodectus
Local pinprick is almost always felt.
Muscle cramp–like spasms occur in
large muscle groups.
Immediate mild to moderate pain
occurs.
Physical examination of the
“cramping” extremity rarely reveals
rigidity.
Pain may spread quickly to include
the entire extremity.
Pain increases and becomes
generalized, involving the trunk,
back, and abdomen.
Erythema appears approximately 20
to 60 min after the bite.
Pain lasts for 24 h or longer and can
be intermittent.
Erythema evolves into a target lesion
1 to 2 cm in diameter.
Severe hypertension may occur.
Severe local pain is felt.
Sympathetic stimulation:
tachycardia, hypertension.
Parasympathetic hyperactivity:
nausea, vomiting, diaphoresis,
salivation.
Phoneutria
Spinal cord impairment: priapism.
Central nervous effects: vertigo,
visual changes.
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Death from respiratory failure can
be seen in 2 to 6 h.
Local pain is felt.
Wheal with surrounding erythema
appears.
Localized sweating and piloerection
occur.
Atrax/Hadronyche
Perioral paresthesias.
Parasympathetic hyperactivity:
nausea, vomiting, diaphoresis,
salivation, lacrimation,
bronchorrhea.
Neuromuscular stimulation: muscle
fasciculation, tremors, spasms,
weakness.
Central nervous system toxicity:
altered level of consciousness.
Death can result from cardiac
arrest, hypotension, or pulmonary
failure.
Spiders Causing Necrotic Arachnidism (Loxosceles)
Loxosceles are brown spiders that have a worldwide distribution. Native species exist in the U.S. (Figure 205-3),
and of these, L. reclusa (the brown recluse spider) occupies the largest geographic area and accounts for the
majority of significant envenomations. In South America, particularly Brazil, L. laeta and L. intermedia account for
most significant envenomations. Envenomation outside of endemic areas is unusual.17 Loxosceles spiders are
nocturnal; are shy; are found both indoors and outdoors in dark, dry areas such as basements, closets, and
woodpiles; and may bite when threatened. A pigmented, violin-shaped pattern on the cephalothorax of the brown
recluse is a distinguishing characteristic (Figure 205-4). However, this characteristic is considered unreliable and
often misinterpreted. Loxosceles species are most accurately identified by their eye pattern, which consists of six
paired eyes (one anterior pair, two lateral pairs).17 Most other U.S spiders have eight eyes arranged in two rows of
four. The venom of the brown recluse contains multiple enzymes, including hyaluronidase and the major one
responsible for necrosis, sphingomyelinase D. Significant necrotic wounds are rare but are possible through
neutrophil activation, platelet aggregation, and thrombosis. Although both local and systemic complications of
Loxosceles envenomation have been well described, it is important to recognize that the perceived threat of the
brown recluse far exceeds its actual danger. For more information about recluse spiders see http://spiders.ucr.edu.
FIGURE 205-3.
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Range of recluse (genus Loxosceles) spiders in the U.S. (Reproduced with permission by Rick Vetter from
http://spiders.ucr.edu/images/colorloxmap.gif.)
FIGURE 205-4.
Close-up look at the characteristic fiddle-shaped back marking on the brown recluse spider (Loxosceles reclusa).
(Photograph by Lawrence B. Stack, MD. Reproduced with permission from Knoop KJ, Stack LB, Storrow AB,
Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill, Inc., New York.)
Clinical Features
Bites by Loxosceles spiders are described as initially painless, which often prohibits possible identification of the
spider. The most common manifestation of a bite is a mild erythematous lesion that may become firm and heal
with little or no scar within several days or weeks. Occasionally, a more severe local reaction occurs, beginning
with mild to severe pain several hours after the bite, accompanied by localized erythema, pruritus, and swelling. A
hemorrhagic blister then forms, surrounded by vasoconstriction-induced blanched skin (Figure 205-5). By day 3 or
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4 the hemorrhagic area may become ecchymotic, which leads to the “red, white, and blue” (erythema, blanching,
and ecchymosis) sign. The ecchymotic area may become necrotic, with eschar formation by the end of the first
week. The necrotic, slowly healing ulcers may not reach maximum size for many weeks after envenomation and
can occasionally result in a significant cosmetic defect requiring skin grafting.
FIGURE 205-5.
Early brown recluse spider bite (approximately 8 hours old) with a violaceous center surrounded by a faint
spreading erythema. (Photograph by Lawrence B. Stack, MD. Reproduced with permission from Knoop KJ, Stack
LB, Storrow AB, Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill, Inc., New York.)
Although significant systemic effects are common after bites of L. laeta, the predominant South American species,
they rarely occur after bites of the brown recluse, the predominant U.S. species. Systemic effects, the hallmark of
which is hemolysis, are seen more often in children and typically occur 24 to 72 hours after the bite. Other effects
include nausea, vomiting, fever, chills, arthralgias, thrombocytopenia, rhabdomyolysis, hemoglobinuria, and renal
failure. Disseminated intravascular coagulation and death are extremely rare.
Correct diagnosis of a brown recluse envenomation without definitive spider identification is difficult. Although the
presence of a consistent clinical picture in an endemic area is suggestive, it is likely that a myriad of infectious and
noninfectious conditions are misdiagnosed as brown recluse bites.17 In patients who are suspected of having
been bitten and who exhibit signs and symptoms of envenomation, a complete blood count should be performed,
blood urea nitrogen and creatinine levels checked, and coagulation profile obtained. Assays to detect
envenomation have been used in research, but a commercial test does not exist.
Treatment
Treatment of possible necrotic spider bite should include the usual supportive measures, including administration
of pain medication. Antibiotics are indicated if signs of infection exist. However, secondary infections are
uncommon.18 Close follow-up for serial wound evaluations should be arranged. If ulceration develops, surgical
debridement is delayed until clear margins are established, often 2 to 3 weeks after the bite.
Patients with systemic symptoms following a bite warrant hospitalization. Various treatments have been advocated
for brown recluse spider bites, including antihistamines, antivenom, colchicine, dapsone, hyperbaric oxygen,
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surgical excision, steroids, and topical nitroglycerin. None of these therapies has shown clear benefit, and most
wounds from the brown recluse are self-limiting and heal without any medical intervention. Administration of the
leukocyte inhibitor dapsone continues to be advocated by some despite lack of supporting research and known
adverse effects, including hemolysis and methemoglobinemia. Of all treatments, antivenom administration holds
the most promise, and in animal models early administration after envenomation has been demonstrated to be
beneficial.18
An equine-derived antivenom is commonly used in Brazil; however, its efficacy is unclear. In the U.S., there is no
commercially available Loxosceles antivenom.
Hobo Spider (Tegenaria agrestis)
A native of Europe and central Asia, the hobo or Northwestern brown spider is now found in the Pacific Northwest
of the U.S. and Canada after its introduction through the port of Seattle in the 1930s. Because of possible similarity
in presentation, hobo spider envenomations in this area are often incorrectly attributed to the brown recluse spider,
which lives elsewhere. As suggested by its scientific name, the species is considered to be aggressive because of
reports of biting with minor provocation. Hobo spiders are brown with gray markings and have a 7- to 14-mm body
length and a 27- to 45-mm leg span. They live in moist, dark areas such as woodpiles and basements.
Clinical Features
The clinical presentation in victims of hobo spider envenomations is similar to that in individuals bitten by the
brown recluse spider. Headache is the most common systemic symptom. Little documentation supports the
occurrence of necrosis from hobo spider bites, and in its native European habitat, it is not considered poisonous to
humans.17
Treatment
There is no diagnostic test for hobo spider envenomation, nor is there proven treatment for local or systemic
complications. Surgical resection with skin grafting may be necessary but should not be initiated until the
necrotizing process is completed.
Widow Spiders (Latrodectus)
Latrodectus or “widow” spiders have a worldwide distribution. In the U.S., the black widow is the most well known,
although of the five Latrodectus species found commonly in the U.S., only three (L. mactans, L. variolus, and L.
hesperus) are actually black. Other varieties may be predominantly brown (L. geometricus) or red (L. bishopi). An
orange-red hourglass-shaped marking characterizes many of the Latrodectus species (Figure 205-6). Female
spiders are relatively large, with a body size ranging up to 1.5 cm in length and leg spans of 4 to 5 cm. The male
spider is approximately one third the size of the female and lighter in color, and his bite cannot penetrate human
skin. Black widow spiders are found most often in woodpiles, basements, garages, and sheds. Latrodectus will
aggressively defend her web, particularly when guarding her eggs. Most black widow bites occur between April
and October and are usually seen on the hands and forearms.
FIGURE 205-6.
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Black widow spider (Latrodectus mactans) with offspring. Note characteristic hourglass marking on abdomen.
(Photograph by Lawrence B. Stack, MD. Reproduced with permission from Knoop KJ, Stack LB, Storrow AB,
Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill, Inc., New York.)
The black widow spider injures its victim and its prey with a highly potent venom. The most active component of
the venom is α-latrotoxin, which acts through both calcium-dependent and calcium-independent pathways leading
to receptor stimulation, pore formation, and ultimately massive release of neurotransmitters (predominantly
acetylcholine and norepinephrine).19
Clinical Features
Most Latrodectus bites are felt immediately as a pinprick sensation at the bite site, followed by increasing local
pain that may spread quickly to include the entire bitten extremity. Erythema appears approximately 20 to 60
minutes after the bite. In many bites, a small, <5-mm erythematous macule develops that may evolve into a larger
target lesion with a blanched center and surrounding erythema (Figure 205-7). The clinical syndrome with
envenomation is referred to as latrodectism. Victims frequently complain of muscle cramp–like spasms in large
muscle groups, although physical examination of the “cramping” extremity rarely reveals rigidity. The pain often
increases progressively, becomes generalized, and can involve the trunk, back, and abdomen. Localized
diaphoresis near the site of envenomation can be seen. Severe abdominal wall musculature pain and cramping is
well described. Hypertension and tachycardia are common, and systemic symptoms include headache, nausea,
vomiting, diaphoresis, photophobia, and dyspnea. Rarely reported complications include atrial fibrillation,
myocarditis, priapism, and death. The pain with envenomation can be severe and intermittent, and if untreated
often lasts for a day. Occasionally, symptoms may persist for several days.
FIGURE 205-7.
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Black widow spider bite on the knee. (Photograph by Gerald O’Malley, DO. Reproduced with permission from
Knoop KJ, Stack LB, Storrow AB, Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill,
Inc., New York.)
Because an immediate pinprick sensation is usually reported with Latrodectus bites, it is common for the offending
spider to be identified. In the absence of a witnessed bite, a clinical diagnosis can be made based on characteristic
symptoms and signs. There is no confirmatory laboratory test.
Treatment
Cleansing of the bite site is reasonable. Pain and muscle spasms can be effectively controlled with liberal doses of
opioids and benzodiazepines in approximately 70% of victims.20 Although IV calcium has been advocated to
relieve symptoms, a retrospective review of 163 patients with Latrodectus envenomation indicated that this
treatment is ineffective.20 For severe envenomations, admission may be required for continued analgesia. The
most effective therapies for severe envenomation are parenteral opioids and Latrodectus antivenom.
Administration of Latrodectus antivenom often causes rapid resolution of symptoms and can significantly shorten
the course of illness. Even in severely symptomatic cases of Latrodectus envenomation, patients can often be
discharged from the ED after a short observation period when antivenom is administered. Latrodectus antivenom is
produced in at least three countries with specificity for indigenous species: Redback (L. hasselti) Spider Antivenom
(CSL Ltd., Melbourne, Australia), Button Spider Antivenom (South African Vaccine Producers Institute, Edenvale,
South Africa), and Antivenin Latrodectus mactans (Merck & Co., Inc., Whitehouse Station, NJ). It is likely that the
antivenom to one species would be clinically effective in treating the bites of the others. Indications, amount, and
route of administration vary according to product. Antivenin Latrodectus mactans and Button Spider Antivenom are
administered IV, and Redback Spider Antivenom is administered by IM injection. Latrodectus antivenom is derived
from horse serum, and hypersensitivity reactions are possible. Redback antivenom is the most frequently used
antivenom in Australia, and adverse reactions are rare. One death from anaphylaxis has been reported after
administration of Antivenin Latrodectus mactans in the U.S.; in that case, however, the antivenom was given
undiluted via IV push to a patient with asthma who had known allergies to multiple medications. Slow
administration of diluted Antivenin Latrodectus mactans is considered safe.21 Successful treatment of latrodectism
with antivenom has been described even with administration 90 hours after envenomation.22 Administration of
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Antivenin Latrodectus mactans is not contraindicated in pregnancy.23
Armed Spiders (Phoneutria)
The armed spiders of South America are aggressive hunters and possess potent neurotoxic venom. Being
nocturnal hunters, the spiders may enter houses during the night and hide in clothes during the day. These spiders
have also been reported to hide in banana bunches during shipping and can bite workers handling these bananas
at their destination. The best-known armed spider, Phoneutria nigriventer, is large, with a body size up to 3.5 cm
and leg length up to 6 cm. P. nigriventer venom contains a mixture of potent neurotoxins that produce central
nervous system, spinal cord, and autonomic effects.
Clinical Features
The majority of P. nigriventer bites are reported to produce no significant symptoms. Significant envenomation
produces local symptoms (severe pain) followed by sympathetic stimulation (tachycardia, hypertension),
parasympathetic hyperactivity (nausea, vomiting, diaphoresis, salivation), spinal cord impairment (priapism), and
central nervous system effects (vertigo, visual changes). Death from respiratory failure can occur in 2 to 6 hours,
usually in children or debilitated adults. Most healthy adults recover in 1 to 2 days.
Treatment
In most cases, supportive care is adequate. Local anesthetic infiltration at the bite site is useful for local pain
control. A polyvalent antivenom (Instituto Butantan, São Paulo, Brazil) is available for cases of severe
envenomation from P. nigriventer. Use of opioids for pain control is contraindicated in severe envenomation,
because they appear to enhance the adverse effect of venom on respiration.
Funnel-Web Spiders (Atrax/Hadronyche)
Funnel-web spiders are so named because they construct a cylindrical web that extends into a recess, such as a
burrow in the ground or a hole in a tree. Medically significant funnel-web spiders are found in southern and
southeastern Australia and in the adjacent islands of Tasmania, Papua New Guinea, and the Solomon Islands.
Funnel-web spiders of this region were originally classified into the genera Atrax and Hadronyche, but are now
considered one genus. To prevent confusion, species are identified using their original genus names.
Funnel-web spiders have a shiny black body and long fangs, and females can grow up to 4 cm in body length.
Females stay close to their webs, but the smaller and more aggressive males tend to wander, especially during the
summer following a rain. Atrax venom contains a potent mixture of neurotoxins with neuromotor and autonomic
effects.
Clinical Effects
Atrax bites may result in local reaction with immediate pain, followed by wheal formation and surrounding
erythema. Later, localized sweating and piloerection may be observed. The vast majority of Atrax bites do not
result in significant envenomation or systemic toxicity. Symptoms and signs of systemic toxicity include perioral
paresthesias, parasympathetic hyperactivity (nausea, vomiting, diaphoresis, salivation, lacrimation, bronchorrhea),
neuromuscular stimulation (muscle fasciculation, tremors, spasms, weakness), and central nervous system toxicity
(altered level of consciousness). Death after A. robustus envenomation has been reported as a result of cardiac
arrest, hypotension, or pulmonary failure occurring between 15 minutes and 3 days after a bite.
Treatment
To reduce venom absorption and systemic toxicity from a bite on an extremity, a compressive elastic
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bandage should be applied the entire length of the limb and the extremity should be splinted to prevent
movement. The victim should be immobilized and transported promptly to the hospital.
The specific treatment for systemic toxicity is Funnel-Web Spider Antivenom (CSL Ltd., Melbourne, Australia). If
the patient has signs of systemic toxicity upon arrival or develops them after the compressive elastic bandage is
carefully removed, two ampules of antivenom should be administered IV every 15 minutes until symptoms improve.
Most reported cases require four vials. Supportive therapy for hypotension (IV fluid), bronchorrhea (atropine),
tremors and agitation (benzodiazepines), and hypertension and tachycardia (β-blockers) may be necessary, but
antivenom is the only therapy known to consistently improve survival.
Sac and Running Spiders (Cheiracanthium)
Cheiracanthium are medium-sized (7- to 15-mm body size and 30-mm leg span) house-dwelling spiders. The
venom is cytotoxic and neurotoxic, but only the South African C. lawrencei appears capable of producing skin
necrosis.
Clinical Features
The most common symptoms are local pain, swelling, and erythema at the bite site. Mild systemic symptoms of
headache, malaise, dizziness, and nausea have occasionally been reported. Skin necrosis following a C. lawrencei
bite typically becomes apparent by the third day and heals in 7 to 10 days.
Treatment
Treatment is symptomatic with local wound care. Even if skin necrosis develops, healing is expected provided no
secondary infection develops.
Tarantulas (Theraphosidae)
Tarantulas are large, hairy spiders belonging to the family Theraphosidae that have become increasingly popular as
pets. The hairs found on the abdomen of most species of tarantulas in North and South America resemble a
velvety covering and are used defensively. When threatened, tarantulas may flick these hairs a short distance with
their two back legs. Although North American tarantula hairs rarely penetrate human skin, the hairs have been
found in some cases to imbed deeply into the conjunctiva and cornea, and can cause inflammation in all levels of
the eye, from conjunctiva to retina. Patients who manifest a red eye and pain after handling a tarantula should
be examined to determine if offending barbed hairs are present in the cornea or conjunctiva. Although hairs
are sometimes easily seen on slit lamp examination, they may at times be very difficult to detect. Therapy includes
surgical removal of the hairs and topical application of steroids to control inflammation. Ophthalmia nodosa is a
granulomatous, nodular reaction that can occur in cases of ocular exposure to tarantula hairs.24 Patients may also
develop a diffuse contact dermatitis from indirect exposure to hair while cleaning a tarantula cage. Bites from
tarantulas are typically painful, with local erythema and edema, and some patients describe local joint stiffness
following bites on nearby areas. Systemic symptoms other than fever are unusual.
Other Spiders
Wolf spiders (Lycosa) are small- to medium-sized (3- to 5-mm body length) ground-dwelling spiders with a
worldwide distribution. The venom is cytotoxic and produces local pain and occasionally induration and erythema,
but no systemic symptoms. The venom is not believed to produce skin necrosis, and the purported cases of
Lycosa skin necrosis probably represent either misidentification of the biting spider or a concomitant infection.
Jumping spiders (family Salticidae) are typically small (<15 mm), brightly colored, and very active spiders with a
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worldwide distribution. A bite may produce pain, swelling, pruritus, and erythema that resolves in 2 days. There are
case reports of minor skin ulceration (U.S.) and headache and vomiting (Australia) after a jumping spider bite.
Daddy long-legs spiders (family Pholcidae) are common cellar and outbuilding dwellers along the Pacific coast and
in southwestern deserts. A repeated myth is that these spiders possess highly toxic venom, but their fangs are too
short to penetrate human skin. This is false. There are no research studies on the effects of Pholcidae venom in
mammals and no case reports of human envenomation.
Scorpions (Scorpionidae)
Scorpions have a worldwide distribution. Highly toxic species are found in the Middle East, India, North Africa,
South America, Mexico, and the Caribbean island of Trinidad. Several species of scorpions are found in the
warmer parts of the southern U.S. All are generally nocturnal and capable of stinging humans, but most species
cause little more than localized pain similar to that following Hymenoptera stings. In the U.S., only Centruroides
exilicauda (also known as C. sculpturatus), or the bark scorpion, found throughout Arizona, New Mexico, and parts
of Texas and California, possesses venom potent enough to cause systemic toxicity.
Clinical Features
C. exilicauda venom can open neuronal sodium channels and cause prolonged and excessive depolarization.
Somatic and autonomic (parasympathetic and sympathetic) systems may be affected. Systemic symptoms from
the sting of this scorpion are not common but can be severe, particularly in children. Immediate onset of pain and
paresthesias in the stung extremity is usually noted and may become generalized. In severe cases, cranial nerve
and somatic motor dysfunction can develop, resulting in abnormal roving eye movements, blurred vision, and
pharyngeal muscle incoordination and drooling, and can occasionally lead to respiratory compromise. Excessive
motor activity may present as restlessness or uncontrollable jerking of the extremities that appears to be
seizurelike activity. Nausea, vomiting, tachycardia, and severe agitation can also be present. Without antivenom
treatment, symptoms can last 24 to 48 hours. Localized symptoms also predominate after envenomation with
potentially more dangerous scorpions outside of the U.S. However, severe systemic symptoms are well described.
When death occurs the cause is typically cardiogenic shock and pulmonary edema.
Diagnosis of a scorpion sting is clinical. Stings can be confused initially with anything that causes local pain,
particularly in children. As the syndrome progresses in moderate to severe cases to include autonomic and motor
findings, the diagnosis should become more apparent.
Treatment
Initial treatment is supportive with analgesics and benzodiazepines. Atropine may be given for hypersalivation and
respiratory distress due to Centruroides,25 but atropine is contraindicated for the treatment of many foreign
scorpion stings because it may exacerbate adrenergic effects. Atropine may be safer with Centruroides stings
because the adrenergic effects of the venom are much less pronounced than those from other scorpion stings.
Scorpion antivenom directed against different species has been produced for research or clinical use in >10 other
countries. Recommendations for use and dosing of these products vary widely. Like all animal-derived antivenoms,
both immediate and delayed allergic reactions, including serum sickness, are possible. A recent randomized,
double-blind study from Arizona in children suffering from the neurotoxic effects of Centruroides stings
demonstrated that an intravenous scorpion-specific antibody resolved the clinical syndrome within 4 hours, and
reduced the need for concomitant sedation.26
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Ticks (Ixodes, Dermacentor, and Others)
Ticks are found throughout the world, mostly in rural areas. They are obligate bloodsucking arthropods that are
second only to mosquitoes in numbers of pathogens vectored to humans. Their bodies consist of a fused
abdomen and thorax in an oval shape, and they vary from 1 mm or less in length to >1 cm when engorged with
blood. Ticks attach to humans painlessly with strong jaws and cementlike adhesive.
The main concern regarding ticks is that they are disease vectors. Viruses, bacteria (including spirochetes and
rickettsiae), and protozoa may all be transmitted by ticks. Lyme disease, Rocky Mountain spotted fever,
ehrlichiosis, babesiosis, Colorado tick fever, tularemia, tickborne relapsing fever, and tickborne encephalitis are all
tick-transmitted diseases. Lyme disease is caused by the Borrelia burgdorferi spirochete transmitted in the U.S. by
the bite of Ixodes scapularis. Certain species of ticks in the U.S. (Dermacentor andersoni and D. variabilis) and
Australia (I. holcyclus) have a neurotoxin and are capable of inducing tick paralysis, a symmetric ascending flaccid
paralysis associated with loss of deep tendon reflexes. Most cases have been reported in children, and the
presentation can be nearly identical to that of Guillain-Barré syndrome, including progression to respiratory
paralysis. A diagnosis of Guillain-Barré syndrome should not be considered until after a thorough search of
the body, including the hair, for an engorged tick. Sensory abnormalities and an elevation of cerebrospinal fluid
protein level do not occur as a result of tick paralysis. In addition, the progression and resolution of symptoms
(with tick removal) is typically faster than recovery from Guillain-Barré syndrome. Recovery from the form that
occurs in Australia is slower, and a dog-derived antivenom exists to treat it.
Use of insect repellants and tight-fitting clothing can be helpful in preventing tick bites, and a daily tick check is
reasonable in tick-infested areas. Various methods, including use of organic solvents, heat, and petrolatum, have
been advocated to aid in tick removal. The generally recommended method is mechanical and involves grasping
the tick with forceps or fine-point tweezers near the point of attachment and pulling straight outward with steady,
gentle traction. Transmission of pathogens is time dependent, so prompt removal of ticks is important.
Chiggers (Trombiculidae)
Chigger infestations result from mite larvae feeding on host skin cells. Mites are found in almost every habitat, are
0.3 to 1.0 mm in length, and the larvae attach themselves to host skin with mandibular structures. They tend to
attach in areas where an obstacle like tight-fitting clothing is met, such as at the tops of socks, the leg bands of
underwear, the waistband, or the edges of a bra. Once attached, the larvae release digestive enzymes to liquefy
epidermal cells. The combination of digestive enzymes secreted by the mite and subsequent host immune
response produces the “chigger bite.”
Clinical Features
Although diseases such as rickettsialpox and scruff typhus have been spread by mite vectors, the major clinical
manifestation of chigger infestation is most often intense pruritus. The attached chigger may be seen initially as a
bright red fleck on the skin, and it, along with the larvae, may be easily scratched off. Lesions are intensely pruritic
and often appear as grouped papules or papulovesicles. The localized allergic response may last for weeks, and
significant excoriation may occur at the site from intense scratching.
The diagnosis of chigger infestation may be difficult, because many other arthropods cause similar clinical
manifestations. The history of outdoor exposure combined with the presence of signs and symptoms localized to
areas of snug-fitting clothing may be helpful.
Treatment
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Treatment is primarily symptomatic to control the itching and consists of oral antihistamines and topical steroids.
Oral steroids may be helpful in severe cases. Chiggers themselves may be killed with permethrin and other topical
scabicides. If secondary infection occurs, antibiotics are indicated.
Mosquitos, Flies, Fleas, and Lice (Diptera)
Mosquitoes
Mosquitoes are water-breeding arthropods found in all parts of the world. Like other members of this group, they
possess one pair of wings, the second pair having evolved into smaller structures used as stabilizers.
Mosquitoes penetrate skin with the piercing motion of a bayonetlike proboscis. The actual puncturing of the skin
surface causes minimal trauma and frequently is not felt by the host. A local anesthetic is injected into the wound
that causes local tissue damage and local hypersensitivity. Bites can lead to both immediate and delayed
reactions. An immediate skin reaction includes redness, a wheal, and itching. A delayed reaction can occur and
usually consists of edema and pruritus. The immediate reaction tends to be of short duration, whereas a delayed
reaction may persist for hours, days, and even weeks. Severe local reactions with skin necrosis are possible.
Patients can acquire allergy to mosquito saliva constituents and develop symptoms consisting of an escalating
reaction to seasonal exposures with increasingly pronounced edematous and pruritic lesions, sometimes
accompanied by fever, malaise, generalized edema, severe nausea and vomiting, and necrosis with resulting
scarring. Treatment is symptomatic with antihistamines and NSAIDs.
The greatest danger from mosquitoes is the transmission of disease. Even with extensive pest control programs,
arbovirus infections and malaria are epidemic in many parts of the world. Japanese B encephalitis, yellow fever,
dengue hemorrhagic fever, and various types of equine encephalitis are among the many viruses transmitted by
mosquitoes. In addition, West Nile virus has recently spread west across North America.27 Malaria is also
encountered frequently in patients in the U.S. after travel and in immigrant populations from areas where malaria is
endemic. Insect repellents offer some protection from mosquito bites.
Flies
Bloodsucking flies range in size from the tiny sand fly, approximately 1 to 3 mm in length, to horseflies, which can
be >2 cm. All flies stab and pierce the skin, causing some degree of pain and pruritus. Several species, such as
deerflies, blackflies, horseflies, and sand flies, can produce allergic reactions, although these are rarely as severe
as those produced by Hymenoptera venom. There is also the possibility of myiasis (infestation of tissue with fly
larvae) from fly bites, but this condition is rare in the U.S.
The diagnosis of fly bite depends chiefly on the patient’s history and a knowledge of the arthropods that frequent
the area of encounter. Treatment for most local reactions to Diptera bites is symptomatic, and treatment of
systemic reactions is the same as for reactions to Hymenoptera venom. Application of cold compresses may
alleviate localized edema. Secondary infection of Diptera bites can occur, and antibiotics may be necessary in
some cases. Oral antihistamines may be helpful in relieving pruritus from fly bites, but topical steroids can be used
when local reactions are severe, and oral steroids are indicated when systemic hypersensitivity symptoms are
present.
Fleas (Siphonaptera)
Bites of fleas, lice, and scabies mites produce lesions so similar that diagnosis is often difficult. Flea bites are
frequently found in zigzag lines, especially on the legs and in the waist area. The lesions most often have a
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hemorrhagic-appearing center surrounded by erythematous and urticarial patches. Flea bites are usually quite
pruritic, and red spots can persist at bite sites for some time.
The main concern in the treatment of these bites is the possibility of secondary infection. Children may develop
impetigo as a complication. The lesions should be washed thoroughly with soap and water. Children with flea bites
should have their fingernails cut short to prevent scratching. To relieve discomfort and itching, local application of
calamine, cool soaks, and oral or topical antihistamines may be helpful. For severe discomfort, application of a
topical steroid cream or spray may be necessary. If secondary infection develops, topical or oral antibiotics may be
needed.
Kissing Bugs and Bed Bugs (Hemiptera)
The order Hemiptera includes two bloodsucking families of arthropods with medical importance. These are
Reduviidae (reduviids, or “kissing” bugs) and Cimicidae (“bedbugs” and their relatives). Various species of kissing
bugs are found predominantly in the southern U.S. and Central and South America. The common name “kissing
bugs” derives from their habit of feeding at night on any exposed surface of a sleeping victim, commonly the face.
Bedbugs are also nocturnal feeders, and their distribution is worldwide. Both bugs are attracted to warm bodies
and hide near beds. Bedbugs are found in nearby cracks and crevices. Both bugs are potential vectors for disease.
Kissing bugs of Central and South America are vectors of Chagas disease (trypanosomiasis).
Clinical Features
Bites from both bugs are typically painless. Erythematous papules, bullae, and wheals may develop.
Diagnostically, kissing bug bites can be differentiated from bedbug bites in that kissing bug bites are not in a linear
formation and usually are not accompanied by telltale brown or black patterns of excrement on the bed linen,
which is characteristic of bed bugs.28 A thorough search of bedding and nearby cracks and crevices will often
reveal the bugs.
Treatment
Treatment of both types of bite is symptomatic. Cool compresses, topical steroids, and antihistamines can be
used to relieve associated pruritus. Some individuals become highly sensitive to kissing bugs and react with
systemic allergic symptoms following a bite. They should be treated as previously outlined for Hymenoptera
envenomation.
Caterpillars and Moths (Lepidoptera)
Lepidopterism refers to the adverse effects resulting from contact with butterflies, moths, or their caterpillars. With
the exception of dermatitis caused by female moths of the Hylesia genus found in Central and South America,
most symptoms are a result of contact with caterpillars.
Clinical Features
Caterpillars are the larval stage of moths and have either spines or hairs for protection. The spines can be hollow,
branched, and connected to a venom gland. The spines and hairs may cause mechanical irritation, whereas the
venom can produce additional symptoms. The vast majority of caterpillars are harmless to humans. Pruritus from
localized “caterpillar dermatitis” and occasional diffuse urticaria are the predominant symptoms of exposures to
the hairs and venom. The puss caterpillar (Megalopyge opercularis) is found in the southeastern U.S. and accounts
for most of the serious envenomations in this country. After initial contact, intense local burning pain rather than
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pruritus is typical. A gridlike pattern of hemorrhagic papules may be seen within 2 to 3 hours of these exposures
and may last for several days. Regional lymphadenopathy is common, and the affected limb can swell
considerably. Other symptoms include headaches, fever, hypotension, and convulsions. No deaths have been
reported. Ingestions of the hickory tussock caterpillar (Lophocampa caryae), found in the eastern U.S., have been
reported with symptoms ranging from drooling to diffuse urticaria. Spines have been visualized in the oropharynx
and even the esophagus in some of these patients, requiring general anesthesia to aid in removal.28
Treatment
No antivenom exists for lepidopterism, and treatment is symptomatic and supportive. Spines can be removed
using adhesive tape. Antihistamines and steroids may be administered for pruritus. For the rare patient with
hypotension, IV fluids and SC epinephrine should be administered.
Blister Beetles (Coleoptera)
Although the order Coleoptera includes a large number and variety of beetles, clinically significant envenomation
occurs only from blister beetles. There are approximately 1500 species of blister beetles worldwide, including 200
species in the U.S. Although it is not naturally found in the U.S., the most well-known blister beetle is the “Spanish
fly” (Cantharis vesicatoria).
Clinical Features
Blister beetles contain the highly potent vesicant cantharidin, which is exuded from their joints when disturbed or
from their body when crushed. For this reason, a blister beetle should be removed from the skin by blowing or
flicking. Cantharidin-containing preparations are used medicinally in wart removal. Application of these
substances in low concentration is without adverse effect.29 However, higher concentrations or contact with the
beetle’s venom may cause local inflammation leading to bullae formation. Severe conjunctivitis may also occur if
cantharidin contacts the eyes from contaminated hands.
High concentrations of cantharidin may result in dermal absorption and systemic toxicity. Systemic toxicity also
occurs following ingestion, either of the whole beetle or of cantharidin-containing preparations. Severe vomiting,
hematemesis, abdominal pain, and diarrhea may occur, followed by dysuria, hematuria, oliguria, and renal failure
because the toxin is concentrated in the kidneys. Death has occurred after large ingestions. Although the exact
mechanism by which cantharidin produces systemic toxicity is unknown, the vesicant action may explain many of
the symptoms observed. Fortunately, most preparations sold as “Spanish fly” for their purported aphrodisiac
properties have very low concentrations of cantharidin. The local vascular congestion and urethral inflammation
that occurs following ingestion may be interpreted by some as enhanced sexuality.
Treatment
Treatment of blister beetle toxicity is largely supportive. The skin should be irrigated thoroughly after topical
exposure to remove any persistent cantharidin, followed by local wound care. Patients who are symptomatic after
ingestion should be admitted and treated supportively.
References
1. White J: Bites and stings from venomous animals: a global overview. Ther Drug Monit 22: 65, 2000. [PubMed:
10688262]
2. Bronstein AC, Spyker DA, Cantilena LR Jr, et al: 2008 Annual report of the American Association of Poison
http://accessemergencymedicine.mhmedical.com.ezproxy.uky.edu/content.aspx?bookid=693&sectionid=45915552
24/26
2/15/2015
Control Centers' National Poison Data System (NPDS): 26th Annual Report. Clin Toxicol 47: 1026, 2009.
3. Stibich AS, Carbonaro PA, Schwartz RA: Insect bite reactions: an update. Dermatology 202: 193, 2001. [PubMed: 11385222]
4. Diaz-Sanchez CL, Lifshitz-Guinzberg A, Ignacio-Ibarra G, et al: Survival after massive (>2000) Africanized
honeybee stings. Arch Intern Med 158: 925, 1998. [PubMed: 9570180]
5. Betten DP, Richardson WH, Tong TC, Clark, RF: Massive honey bee envenomation-induced rhabdomyolysis in
an adolescent. Pediatrics 117: 231, 2006. [PubMed: 16396886]
6. King TP, Spangfort MD: Structure and biology of stinging insect venom allergens. Int Arch Allergy Immunol 123:
99, 2000. [PubMed: 11060481]
7. Antonicelli L, Bilo MB, Bonifazi F: Epidemiology of Hymenoptera allergy. Curr Opin Allergy Clin Immunol 2: 341,
2002. [PubMed: 12130949]
8. Lazoglu AH, Boglioli LR, Taff ML, et al: Serum sickness reaction following multiple insect stings. Ann Allergy
Asthma Immunol 75: 522, 1995. [PubMed: 8603283]
9. Jones RGA, Corteling RL, To HP, et al: A novel Fab-based antivenom for the treatment of mass bee attacks.
Trop Med Hyg 61: 361, 1999. [PubMed: 10497971]
10. Hamilton RG: Diagnostic methods for insect sting allergy. Curr Opin Allergy Immunol 4: 297, 2004. [PubMed:
15238796]
11. Kemp SF, deShazo RD, Moffitt JE, et al: Expanding habitat of the imported fire ant (Solenopsis invicta): a public
health concern. J Allergy Clin Immunol 105: 683, 2000. [PubMed: 10756216]
12. deShazo RD, Kemp SF, deShazo MD, Goddard J: Fire ant attacks on patients in nursing homes: an increasing
problem. Am J Med 116: 843, 2004. [PubMed: 15178500]
13. McGain F, Winkel KD: Ant sting mortality in Australia. Toxicon 40: 1095, 2002. [PubMed: 12165310]
14. Fernandez-Melendez S, Miranda A, Garcia-Gonzalez JJ at el: Anaphylaxis caused by imported red fire ant
stings in Málaga, Spain. J Investig Allergol Immunol 17: 48, 2007. [PubMed: 17323863]
15. Koya S, Crenshaw D, Agarwal A: Rhabdomyolysis and acute renal failure after fire ant bites. J Gen Int Med 22:
145, 2007. [PubMed: 17351856]
16. Goddard J: Personal protection against fire ant stings. Ann Allerg Asthma Immunol 95: 344, 2005. [PubMed:
16279564]
17. Swanson DL, Vetter RS: Bites of brown recluse spiders and suspected necrotic arachnidism. N Engl J Med
352: 700, 2005. [PubMed: 15716564]
18. Pauli I, Puka J, Gubert IC, Minozzo JC: The efficacy of antivenom in loxoscelism treatment. Toxicon 48: 123,
2006. [PubMed: 16808942]
19. Ushkaryov YA, Volynski KE, Ashton AC: The multiple actions of black widow spider toxins and their selective
use in neurosecretion studies. Toxicon 43: 527, 2004. [PubMed: 15066411]
20. Clark RF, Wethern-Kestner S, Vance MV, Gerkin R: Clinical presentation and treatment of black widow spider
envenomation: a review of 163 cases. Ann Emerg Med 21: 782, 1992. [PubMed: 1351707]
21. Clark RF: The safety and efficacy of antivenin Latrodectus mactans. J Clin Toxicol Clin Toxicol 39: 125, 2001. [PubMed: 11407497]
22. Successful treatment of latrodectism with antivenin after 90 hours. N Engl J Med 340: 657, 1999.
23. Sherman RP, Groll JM, Gonzalez DI, Aerts MA: Black widow spider (Latrodectus mactans) envenomation in a
term pregnancy. Curr Surg 57: 346, 2000. [PubMed: 11024247]
24. Belyea DA, Tuman DC, Ward TP, Babonis TR: The red eye revisited: ophthalmia nodosa due to tarantula hairs.
South Med J 91: 565, 1998. [PubMed: 9634120]
25. Suchard JR, Hilder R: Atropine use in Centruroides scorpion envenomation. J Toxicol Clin Toxicol 39: 595,
2001. [PubMed: 11762667]
26. Boyer LV, Theodorou AA, Berg RA. et al: Antivenom for critically ill children with neurotoxicity from scorpion
stings. N Eng J Med 360: 2090, 2009. [PubMed: 19439743]
http://accessemergencymedicine.mhmedical.com.ezproxy.uky.edu/content.aspx?bookid=693&sectionid=45915552
25/26
2/15/2015
27. Vetter R: Kissing bugs (Triatoma) and the skin. Dermatol Online J 7: 6, 2001. [PubMed: 11328627]
28. Kuspis DA, Rawlins JE, Krenzelock EP: Human exposures to stinging caterpillar: Lophocampa caryae. Am J
Emerg Med 19: 396, 2001. [PubMed: 11555796]
29. Moed L, Shwayder TA, Chang MW: Cantharidin revisited: a blistering defense of an ancient medicine. Arch
Dermatol 137: 1357, 2001. [PubMed: 11594862]
Useful Web Resource
Spider Research, University of California, Riverside—http://spiders.ucr.edu
WHO snake bite Web site—http://www.who.int/bloodproducts/snake_antivenoms/en/
Copyright © McGraw-Hill Global Education Holdings, LLC.
All rights reserved.
Your IP address is 128.163.2.206
Representative venomous Hymenoptera. A. Hornet (Vespula maculata). B. Wasp (Chlorion ichneumerea). C. Yellow
jacket (Vespula maculiforma). D. Honeybee (Apis mellifera). E. Fire ant (Solenopsis invicta). (Reproduced with
permission from Merck, Sharp & Dohme, Division of Merck & Co., Inc.)
Fire ant bites. These bites on the anterior knee occurred when the patient knelt on a fire ant mound. The bites are 3
days old. The initial sterile pustules have begun to crust over. (Photograph by Alan Storrow, MD. Reproduced with
permission from Knoop KJ, Stack LB, Storrow AB, Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009
by McGraw-Hill, Inc., New York.)
Range of recluse (genus Loxosceles) spiders in the U.S. (Reproduced with permission by Rick Vetter from
http://spiders.ucr.edu/images/colorloxmap.gif.)
Close-up look at the characteristic fiddle-shaped back marking on the brown recluse spider (Loxosceles reclusa).
(Photograph by Lawrence B. Stack, MD. Reproduced with permission from Knoop KJ, Stack LB, Storrow AB,
Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill, Inc., New York.)
Early brown recluse spider bite (approximately 8 hours old) with a violaceous center surrounded by a faint
spreading erythema. (Photograph by Lawrence B. Stack, MD. Reproduced with permission from Knoop KJ, Stack
LB, Storrow AB, Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill, Inc., New York.)
Black widow spider (Latrodectus mactans) with offspring. Note characteristic hourglass marking on abdomen.
(Photograph by Lawrence B. Stack, MD. Reproduced with permission from Knoop KJ, Stack LB, Storrow AB,
Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill, Inc., New York.)
Black widow spider bite on the knee. (Photograph by Gerald O’Malley, DO. Reproduced with permission from
Knoop KJ, Stack LB, Storrow AB, Thurman RJ: The Atlas of Emergency Medicine, 3rd ed, © 2009 by McGraw-Hill,
Inc., New York.)
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