Hookworm
Department of Medical Parasitology
Introduction
• Hookworm refers to nematodes of Family
Ancylostomatidae
• Highly developed buccal capsule -- remarkable
morphological characteristic of adults
• Adults parasite in small intestine and result in
hookworm disease, heavy infection may evoke
anemia known as Yellow Laziness
• World-wide distribution, about 900 million
infections in the world
• The most harmful one among human digestive
track nematodes
Classification and Species
1. Classification
Phylum Nemathelminthes
Class Nematoda
Order Strongylata
Family Ancylostomatidae
2. Species
Ancylostoma duodenale，A.d
Necator americanus，N.a
Morphology -- Adult
• A.d -- “C” shape; N.a -- “S” shape
• Pinkish-white in color, white when fixed
with formalin
• Male -- 5 to 10cm, female -- 9 to 12mm
A.d
N.a
• Head--curved dorsally, giving hooked
appearance, from which the name
“hookworm” is derived
• Buccal capsule
A.d--contains two pairs of actual teeth
N.a--contains a pair of cutting plates
• Posterior end of
male--copulatory
bursa
• Branches of dorsal
ribs
A.d--1, 2, 3
N.a--0, 2, 2
Morphology -- Larva
Rhabditiform larva and filariform larva
Rhabditiform larva
Filariform larva
Morphology -- Egg
• Ovoid in shape, 60×40μm in average, embryo
cells inside
• Thin, clear and colorless egg shell, eggs
recovered in freshly passed stool are usually at
four-cell stage
• A clear space between the developing embryo
and the thin eggshell
Life cycle
Adults
Human
Eggs
molt 2 times
Rhabditiform
larvae
Soil
molt 2 times
Filariform
larvae
Human
Adults
Development in Man
Infection
Stage
Mode
Filariform larvae
(infective stage larvae)
Penetrate through skin
Oral ingestion
Development in Man
Larval migration
filariform
larvae
subcutaneous
tissue
bronchi, trachea
pharynx
esophagus
（5-7wks）
small vein
alveoli
stomach
heart
capillaries
lung
small
intestine
Development in Man
Residence
Stage
Site
Adults
Upper intestine
Mode
Bite intestinal mucosa by
mouth capsule
Feed
Blood, tissue fluid,
intestine mucosa
Development in Man
Residence
Habitus
Change biting place frequently
A.d 10000~30000/day/♀
Fecundity
N.a 5000~10000/day/♀
A.d
Life span
N.a
7 years±
13~15 years
Development in Man
Development in Man
Discharge
Stage Eggs
Mode In the feces
Development in Soil
Process
Eggs
Rhabditiform
larvae
Filariform
larvae
Development in Soil
Suitable condition
Warm (25~30℃)
Moist (relative humidity 60%~80%)
Shaded
Sufficient oxygen (loose soil)
Development in Soil
Characteristics of filariform larvae
Upward
Towards moist
Towards warm
Pathogenesis
Pathogenesis caused by hookworm
infections is attributed to
• The host immune response
• Effects of larval migration
• Mechanical effects of the adults
• Blood loss
Damage of larvae
Dermatitis
"ground itch"
Clinical feature
Allergic itching, pimple,
water blister, etc.
Predilection site
Skin of hands, feet that contact with infected
soil, particularly the areas thin and tender
Damage of larvae
Pneumonia
Clinical feature
Sore throat, bloody sputum, bronchial asthma,
eosinophilia, wheezing, mild pneumonia with
cough, etc.
Damage of adults
Gastrointestinal symptoms
Clinical feature
“Yellow Laziness”, fatigue, weakness,
abdominal pain, epigastric discomfort,
nausea, vomiting, diarrhea with black
to red stools, etc.
Damage of adults
Anemia
Anemia is the most significant
damage caused by hookworm
Type of anemia
Microcytic hypochromic anemia
(iron deficiency anemia)
Damage of adults
Anemia
Ways of blood loss
(secrete anticoagulant)
Direct ingestion of blood by the worms;
blood loss from the attachment site,
continued blood loss from the original
attachment site
Damage of adults
Anemia
Clinical feature
Giddy, listlessness,
palpitation, anhelation;
waxen, pallor, edema of the face and feet;
cardiomegaly, glossitis, koilonychia, etc.
Damage of adults
Allotriophagy
Common neuropsychiatric
disorders due to
hookworm disease
May result from the
enormous loss of iron
Laboratory Diagnosis
• Microscopic identification of eggs
collected in stool. The eggs are
best seen in the brine floatation
• The larvae may be cultivated by
fecal culture in a test tube
Epidemiology
Geographical distribution
•
A. duodenale is prevalent in southern Europe,
north Africa, northern Asia (north China)
•
N. americanus is the predominant species in
the western hemisphere and equatorial Africa
(south China)
•
Many areas are endemic for both species
Source of infection
Patients and carriers
Prevalent factors
Relations to natural environment：
Suitable temperature is around 22~26℃ for
larval development of A.d, and 31~35℃ for
that of N.a
Source of infection
Patients and carriers
Prevalent factors
Relations to crops：
Dry crops such as sweet potatoes, corn,
vegetables, tobacoo, cotton, sugarcane, etc.
Treatment and prevention
• Albendazole / Mebendazole
• Correct anemia
• Sanitary disposal of feces
• Avoidance of contact with soil by
wearing shoes and gloves
• Modernization of agricultural
techniques