Parasitic Protozoa
Slackers Facts by Mike Ori
Disclaimer
The information represents my understanding only so errors and omissions are
probably rampant. It has not been vetted or reviewed by faculty. The source is our
class notes.
The document can mostly be used forward and backward. I tried to mark
questionable stuff with (?).
If you want it to look pretty, steal some crayons and go to town.
Finally…
If you’re a gunner, buck up and do your own work.
What are the three related sporozoans?
Toxoplasmosis
Cryptosporidium
Plasmodia
What is the definitive host for toxoplasmosis?
What are the routes of acquisition for
toxoplasmosis?
1. Ingestion of undercooked meat especially
lamb and pork (vive la France)
2. Cat feces
3. Vertical
Explain when toxo is a concern during transplant
When a seropositive donor heart is transplanted
into a seronegative recipient
What results from post transplant infection
Myocarditis
What sx would you expect to see in aids pt
Ring enhancing lesions in the brain
Since toxo increases in aids pt, what type of
immunity is likely to play a role in toxo
control?
Cell mediated immunity
What is the source of toxo in aids pt
Usually reactivated encysted (bradyzoites)
organisms
What is a common source of diarrhea in PT with
low CD4+ counts?
Cryptosporidium
Describe the disease course in
immunocompetent and immunocompromised
pt
Competent: incubation < 2 weeks with 1 week
sx.
Immunocompromised: long term diarrhea
What is the treatment for cryptosporidium in
immunocompromised pt
Raise the CD4 count.
What organism could cryptosporidium be
mistaken for in “regular stains”?
Candida
How do you differentiate cryptosporidium from
candida
Crypto is acid fast, Candida is not
Why is crypto hard to treat
The organisms invades the ciliated surface and
sits in an intracellular but extracytoplasmic
location. This limits access to antimicrobial
agents.
Describe Girardia morphology
Flagellated pear shaped organisms with two
nuclei and a concave sucking disk
Describe Giardia epidemiology
Outdoorsy people that drink from streams
without properly treating the water.
What are girardia’s sx?
Most are asymptomatic. Those that have sx
experience loose foul smelling stools,
abdominal ramps, bloating, weight loss.
Explain how Girardia attaches to the host
It uses its ventral sucking disk for attachment.
How many nuclei does the encysted Giarardia
have
Quattro
Which test is more sensitive, O and P or
fluorescent antibodies, or ELISA
O and P is not very sensitive especially if the
small intestine is colonized.
O and P is repeated three.
Three tests are typically done. FA and ELISA are
much more sensitive and usually yield results
in one test.
What is the string test?
PT’s with small intestinal disease swallow the
end of a string overnight in an effort to trap
organisms in the string for detection.
What is metabolically unique about anaerobic
protozoans?
They do not synthesize nucleotides
Name three anaerobic protozoans
Girardia, Entamoeba, Trichomonas
Describe the SX with Entamoeba infection
Bloody diarrhea
When is Entamoeba infection not a clinical
problem
Entamoeba dispar is a frequent colonizer but is
not known to cause disease. E. histolytica is
only a problem if its invasive.
What is the evidence for invasion with E.
histolytica?
RBC’s ingestion
How are E. dispar and E. histolytica
differentiated?
By PCR
What colon morphology is indicative of
amoebiasis
Inverted flask shaped ulcers.
What is the reservoir for Entamoeba
E. Histolytica = human
What other organs are involved with Entamoeba
and what are the findings
Liver can be involved with anchovy paste filled
cysts. Organisms will be on the periphery of
the cyst.
Describe the sx for trichomonas vaginalis in men
and women
Men are usually asymptomatic
Women will usually have a foul smelling green
discharge
How is Trichmonas vaginalis transmitted?
By sexual contact
Women
How is enamoeba transmitted?
Food > water
How is Girardia transmitted?
Water > food
What is the reservoir for Girardia in the wild
Reservoir = beaver = reservoir builder
What disease does plasmodium cause
Malaria
Name the plasmodium species
P. vivax
P. ovale
P. malariae
P. falciparum
Which species is associated with the most
deaths?
P. falciparum
What is the route of transmission for
Plasmodium
Anopheles
What is the definitive host for malaria
Mosquitoes
What is injected into humans by said mosquito?
A malaria sporozoite
Where do the sporozoites go
The liver
What is a schizont
The replicating malarial mass in a hepatocyte or
RBC
What is a malaria trophozoite?
Something less than a schizont but more than a
merizoite.
Why does malaria fever come in 2-3 day
intervals?
The release of the merizoites from RBC’s is fairly
well coordinated and occurs in a large burst.
This exposes the organism to the immune
system and causes a fever. The merizoites
then go on to infect more RBC’s thus causing a
cycle.
When might the fever cycle degenerate?
P. falciparum tends to degenerate. Multiple
infection cycles also tend to degenerate
What are the unique histological features of P.
falciparum?
Schizont forms tend to lodge in the
microvasculature and so are not seen on
routing blood smears. In addition, more ring
forms and double infected RBC’s are seen in P.
falciparum
What is sequestration
The action of retaining shizonts in the
microvasculature. This prevents removal by
the spleen.
What is unique about the life cycle of P. vivax
and P. ovale?
They can have latent hepatic stages that can
release merizoits months to years later. This is
in contrast to P. falciparum and P. malariae
which release all their merizoites from the
liver in a single go.
Which blood cells does P. vivax invade?
It only invades reticulocytes.
What is the role of receptors in malarial disease
Merizoites interact with species specific
receptors on the RBC surface. For instance P.
vivax required Duffy and reticulocyte receptor
Where are receptors located on merizoites
In a special organelle called the rhoptry
Explain the high incidence of sickle cell trait and
the low incidence of Duffy in west Africa
Sickle cell trait is protective for severe malaria.
Absence of Duffy prevents P. vivax invasion of
reticulocytes. Note there are other examples
in the notes.
Explain the belief that the immune response to
malaria is incomplete
Mortality is highest in naïve pt (children mostly
in endemic areas). Adults can carry a high
parasitemia with little sx and thus seem to be
protected from severe disease.
What are the run of the mill sx for malaria
High fever (40-41c)
Chills
Headache
What is the typical causative species for severe
malaria?
P falciparum
What are the sx of severe malaria
Cerebral malaria – seizures and coma due to
cerebral sequestration
Severe anemia (Hgb < 5) – falciparum can have
very high infectivity
General illness – prostration, hypoglycemia,
lactic acidosis, ARDS
What is chronic malaria
Continuous parasitemia in contrast to recurring
parasitemia
What is the causitive agent for chronic malaria
P. falciparum and P. vivax
What are the methods to prevent malaria
Repellents
Mosquito netting
Clothing
Prophylactic pharmacology
List the malaria time course
Prepatent (hepatic) phase – 2 weeks
Red cell phase – 2-3 days
What is the vector for leishmania
Sand flies
What is an amastigote and a promastigote?
A mastigote = amotile (I.e. no flagella)
Promastigote = pretty good swimmer
(flagellated)
What cell is invaded by promastigotes
Macrophages
What is the result for the macrophage?
Eventual lysis of the cell due to replication
What are the three types of leishmaniasis?
Cutaneous
Mucocutaneous
Visceral
Diffuse cutaneous
Describe cutaneous leishmaniasis
Ulcerative lesions that eventually heal with no
sequelae
Describe mucocutaneous leishmaniasis
Cutaneous lesions heal but later destruction of
nasal and mucosal tissue occurs
Describe visceral leishmaniasis
Invasion of the liver and other visceral leading to
death
Describe diffuse cutaneous leishmaniasis
Treatment resistant non-ulcerative lesions
disseminated over the skin surface. Very tx
resistant.
Describe the African Trypanosoma brucei
species ranges
Roughly divided into east and west african
What is the vector from Trypanosoma brucei
The tsetse fly
Describe the hosts for both species
West = human
East = big game animals with humans as
incidental
What are the stages of african trypanosomal
disease
1. Bite/chancre
2. Hemolymphatic – Lymphadenopathy with
relapsing fever
3. Meningoencephalitis – somnolence, coma,
death
Why does the immune system fail to clear
trypanosomes
The organisms express variant surface
glycoproteins that cause antigenic variation
Describe the progression of T.b rhodesiense and
T.b. ghambiense
Tbr is east african and is much more acute.
Death occurs in months. Tbg is west african
and is less acute. Death occurs on years
How is tx complicated with CNS diease
Tx of CNS disease relies on arsenic containing
compounds which are toxic to the host.
What is the vector for Trypanosoma cruzi
The reduviid bug
How is T. cruzi spread?
The reduviid bug bites a victim causing a
pruritis. The bug also deposits trypanosome
laden feces near the bite. The host then
scratches the bite, mechanically introducing
the organism. The organism can also pass
directly across mucosal surfaces.
What is unique about the epithelial invasion of
T. cruzi
It invades epithelial cells at point of cell to cell
junction.
What are the sx of chagas disease
Nerve destruction
Muscle inflammation and hypertrophy
Leading to dilated cardiomyopathy, arrhythmia,
and GI tract dilation and esophageal
impairment (dysphagia, odynophagia)
What are the phases of chagas disease
Acute
Indeterminate
Chronic
What is Romana’s sign
Periorbital edema caused by T cruzi entry across
the eye mucosa.
What is the cause of most deaths from chronic
chagas disease?
Cardiac disease
What is meant by indeterminate disease
Chagas disease may enter a latent phase that
can lead to acute flares, continued latency, or
chronicity. There is no way to predict the
outcome.
Which phases of chagas disease are treatable?
Acute is treatable. Indeterminate and chronic
do not benefit from treatment.