Protozoology
Dr. Ghidán Ágoston
SE, Institute of Medical Microbiology
Protozoa
Morphology:
• eukaryotic cell with:
– cytoplasmic membrane
– cellular organelles
– 1-2 nuclei
– mitochondria
– cytoplasmic reticulum
• size: from few micrometers  2 mm
Reproduction:
• asexually  DNA replication and division
into 2 cells
• sexually  fusion of 2 cells exchange
DNA and division into 2 cells
Cyst:
• not for reproduction
• biochemically is inactive
Trophozoite:
• the active form
Trophozoite:
• after ingestion cyst  motile and biochemically
active form
• are heterotrophes
Classification (taxonomy):
• they are traditionally classified on the basis of
locomotion:
- Flagellates
- Amoeboids
- Sporozoas
- Ciliates
Protozoa are ubiquitous – can be found in
soil, environments and water
Protozoa also play a vital role in controlling
bacteria population and biomass – sewage
plants
Amoebas
Entamoeba histolitica
Features:
• moves by means of pseudopodia (false
feet)
• most of them live asymptomatically within
the host (carriers)
• transmitted by faecal-oral rout by the
infective form  the cyst (homosexuals
are at high risk)
• the trophozoite cruise along the intestinal
wall
• eating other protozoa, bacteria and RBC
Lifecycle:
• ingested as a mature non-motile cyst 
trophozoites
Virulence factors factors
• germ number: less than 10 cysts are
enough
• adhesive molecules
• Gal/GalNac lectin
• amoeba ionophorin (amoebophorin)
• Histolytic enzymes:
– proteases, cystein kinase, phospholipase A,
hialuronidase, collagenase, elastase, RNase
The name of the disease:
• amoebic dysentery and abscesses
Symptoms:
• mostly asymptomatic
• can invade the intestinal mucosa:
– abdominal pain, mucous & bloody diarrhoea
– if penetrates the portal circulation  liver
abscesses
– reach the diaphragm causing pulmonary
abscesses  death
Diagnosis:
• examine the stool  if a trophozoite is
found with RBC  suggesting an active
disease
• check the number of nuclei in the cyst
• cyst carriers: Ag detection (ELISA)
Entamoeba coli
• is a non-pathogenic species
• is important clinically in humans because it
can be confused with Entamoeba
histolitica which is pathogenic
Therapy
• Amoebic dysentery, extraintestinal
amoebiasis:
– metronidazole (10 days) or tinidazole (5 days)
• Cyst carrier: paromomycin
(aminoglycoside)
Prevention Prevention
• cyst free drinking water (boiling, filtration)
• avoid: raw vegetables, ice cubes
• cysts survive chlorination!
Vaccine candidates:
• a./ recombinant adhesive molecule
• b./ live amoeba, defective for amoebophorin and
cystein kinase
Flagellata
Trichomona vaginalis
Features:
• transmission by sexual contact
• can survive for many hours at room temperature if kept
damp so the theoretical possibility of non-venereal
transmission exists
• occur in female vagina and male urethra
• it has 4 flagella (as the Giardia), central nucleus
• no cyst, only trophozoite form
Trichomoniasis
• symptoms: itching, dysuria
• males are usually asymptomatic or having urethritis
Diagnosis:
• highly motile parasite revealed under the microscope
Treatment:
• Metronidazole, tinidazole
Trypanosoma and Leishmania
Features:
• both are blood borne flagellates
• they are transmitted by the bite of a blood
sucking insect  causing an initial skin
ulcer
Leishmania
Features:
• zoonotic (transmitted from animals to humans)
• carried by rodents, dogs  transmitted by phlebotomine
sandflies
Epidemiology:
• occur in South and Central America, Africa and Middleeast
Lifecycle:
• after transmitted by the fly  ingested by macrophages
 transform to the non-motile amastigote
• the amastigote multiply within the phagocytic cell
• the disease depends on the invasiveness of the parasite
and the cellular immune response of the host
• vary from cutaneous  mucocutaneous and even
visceral involvement
Cutaneous Leishmaniasis
• a fly inject Leishmania into the skin  multiply in
macrophages in the skin
• an ulcer develop on the site of the bite  “oriental sore”
 heals after a year leaving depigmented scar
• when cell immune is intact  skin ulceration
• when immune system is deficient  a nodular skin ulcer
arises but no ulcer  spread diffusely on the body  a
chronic condition
• may metastasize through the bloodstream to sites deep
in the mucosa of the upper respiratory tract, where they
may lie dormant
• after months or years a lesion develops characterized by
necrosis, vasculitis, and tissue destruction
Mucocutaneous Leishmaniasis
• at first a dermal ulcer arises  heals soon
• months to years later  ulcers on the
mucous membrane of the nose and mouth
arise
• can cause erosion of the nasal septum
• superimposed bacterial infection can
cause death
Visceral Leishmaniasis (kala-azar = black sickness)
• the Ganges and Brahmaputra river valleys of India and
Bangladesh are endemic areas
• transmitted by L. donovani or L. chagasi  commonly to
malnourished children
• parasite multiplies in macrophages in the:
– spleen, bone marrow, lymphoid tissues, liver
• months later  abdominal discomfort, fever, anorexia,
hepatomegaly and massive splenomegaly, anemia and ↓
WBC count
• hyperpigmentation is characteristic of visceral
leishmaniasis in India (kala-azar means black sickness)
• fatal if untreated
Treatment:
• sodium stibogluconate
Prevention: insect’s repellents for the sandflies
Post-kala-azar dermal
leishmaniasis
• after recovery from visceral leishmaniasis
20% of Indian patients develop:
– rash on the face and extensor surfaces of the
arms and legs
– in India the rash begins after an interval of 1
or 2 years and progresses over many years
– macules become erythematous plaques or
nodules resembling lepromatous lepros
• it heals spontaneously within 6 months
Sporozoa
Causative agents of malaria
Features:
• malaria is a febrile (high fever) disease caused by 4
different protozoa:
– Plasmodium falciparum (the common and deadly
one)
– Plasmodium vivax
– Plasmodium ovale
– Plasmodium malariae
– Plasmodium knowlesi
• 400-500 million people are infected every year  20-40
million dies
• the vector of the disease is the female anopheles
mosquito  carries the organisms in the salivary
glands injects them while it feeds
• the organism than grow in the liver  spread to
RBC and reproduce  RBC filled with
organisms  bursts  microorganisms released
to the circulation  fever
• the different species burst at other time intervals:
Plasmodium vivax & Plasmodium ovale  burst every
48 hours = tertian malaria (0 hour is one  24h is 2
 48h is 3 = tertian)
Plasmodium malariae  every 72h = quartan malaria
Plasmodium falciparum  burst irregularly between 3648 hours
Lifecycle:
• plasmodia undergo sexual division in the
anopheles mosquito
In the human body:
• the mosquito releases a motile, spindle
shape sporozoites into the blood stream
• it invades the liver and starts the preerythrocyte cycle
• the asexual cycle = schizogony
• the sporozoite forms a ball  trophozoite
• trophozoite undergoes nuclear division 
1000s of new nuclei are formed  a big
mass of them is called schizont
• formation of membrane around the nuclei
 merozoites  burst into the liver and
blood stream  some will infect other liver
cells (as the sporozoite did initially)  a
new cycle is started  exo-erythrocyte
cycle
• those merozoites that enter the blood
stream enter the RBC  starting the
erythrocyte cycle
• the merozoites form trophozoites  a ring
like shape where the nuclear material
looks like a “diamond on the ring”
• nuclear division occurs again forming
schizont  merozoites  lysis of the
RBC and release of the merozoites to the
circulation
• the last step initiate immune response 
resulting in fever chills and sweats
• the merozoites continue this cycle
• some of them will change to female and male
gametocytes  these are taken back by the
mosquito (if not they die after few days)
Important!
• Plasmodium vivax & Plasmodium ovale 
produce dormant form in the liver (hypnozoites)
 grows years after the first infection (
• blood donors must be asked if they had malaria
when they donate blood
In the mosquito:
•
the sexual cycle = sporogony
•
the gametocytes are sucked into the stomach 
female and male gametocytes fuse
•
the DNA is mixed  oocyst is formed
•
oocyst divide to spindle shape sporozoites 
disseminate to the blood stream  reach the salivary
glands  injected into human and the human cycle
starts all over
Symptoms:
• periodic episodes of severe chills and high fever and
sweating
• they run periodically and last 6 hours correlating with the
rapture of the RBC
• the P. falciparum invade >30% of the RBC  anemia
and sticky RBC
• the sticky RBC plugs vessels  haemorrhage and
ischemia  renal failure, pulmonary oedema, coma and
death
• most deaths occur in Sub-Saharan children who develop
cerebral malaria (with seizures and coma)  occurs in
P. falciparum
• hepatosplenomegally occur as the reticuloendothelial
cell clear the lysed RBC`s from the system
• there are some black who have resistance to the
P. vivax and P. falciparum:
• the RBC don’t have membrane Ag named Duffy
a & b  the P. vivax can’t bind to those RBC
• sickle cell anaemia protects the RBC from P.
falciparum invasion
Diagnosis:
• RBC smears to reveal the different stages of the
lifecycle
• fluorescent Ab to identify the species
Prevention:
• eliminate the vector (mosquito)  use
pesticides and repellents
• prophylaxis for traveller’s  chloroquine or
mefloquine/ doxycycline (when the
parasite is resistant to the 1st one)
• P. falciparum has resistance for
chloroquine in some areas of the world
Treatment:
• use the drug of choice: chloroquine
• considerations have to be taken:
– the type of parasite
• P. falciparum resistance to chloroquinie  use
mefloquine, quinine (injected intramuscularly), and
artemisin
• Plasmodium vivax & Plasmodium ovale have the
dormant form (hypnozoites)  Primaquine is used
for that
Toxoplasma gondii
Toxoplasma gondii
Features:
• many animals are infected with
Toxoplasma
• humans are infected by the ingestion of
cyst in undercooked meat or food
contaminated with household cat faeces
• there are also transplacental and
transfusion infections
Lifecycle:
• cat litter box are the most common source for
infection  Toxoplasma gondii
• undergoes sexual division in the cat  secreted
in the faeces as a cyst  absorbed by humans
 ingested by macrophages  transform to
trophozoites
• when cell mediated immune response is intact
 cyst stay as bradyzoites
• it is when the immune system ↓  the disease
breaks
Toxoplasmosis (including the congenital
form)
2 potentially risk groups:
• Immunocompromised patients with AIDS
or those with immunosuppressed therapy
– fever, hepatosplenomegally
– lymphadenopathy
– encephalitis (very common brain
manifestation)
– chorioretinitis is also common  blindness
• The retina shows yellow- white cotton like patches
• It exists in three forms:
– the oocyst, which is excreted with the cat
faeces - can remain viable for months
– the tachyzoite, which multiplies intracellularly
– cysts, the result of this intracellular
multiplication, which can persist as viable
parasites in the brain and striated muscles
throughout the life of the host
• Toxoplasmosis is usually acquired by ingestion of cysts
• organisms spread from the gut by lymphatics and the
bloodstream
• reach every organ, where they multiply intracellularly
(acute stage)
• termination of this stage depends upon the development
of both cellular and humoral immunity
• in immunocompetent hosts, the parasite encysts and will
persist without any inflammatory process as long as the
cysts are not disrupted (chronic stage)
• if the host is immunocompromised, there is a tendency
for the cysts to release bradyzoites and toxoplasma
becomes an opportunistic agent
• congenital infection occurs through transplacental
transmission of tachyzoites when a previously uninfected
woman is infected during pregnancy
• Pregnant women (congenital toxoplasmosis)
– the organism can cross the blood-placenta barrier
– it occurs only if this is the first time a pregnant woman
got infected
– pregnant women should avoid cats!!
– symptoms include:
• blindness, mental retardation, microencephaly, encephalitis,
abortions
– infants that appear normally can develop those
symptoms later in life  reactivation (mostly in the
2nd, 3rd decades of life  causing mostly blindness)
Diagnosis:
• retinal examination, serology (↑ Ig`s) – ELISA,
IF, PCR
Treatment: sulfadiazine and pyrimethamine