Parasites Flashcards
Focus on the parasites mentioned in Flaherty's SAS
Which agent causes hydatid disease?
Echinococcus granulosus (Dog tapeworm)
Hydatid disease = cycstic echinococcosis
How is Leishmaniasis diagnosed?
Skin or bone marrow biopsy or culture
Note: Blood culture will be negative. In humans, Leishmania only has an amastigote form, found in cells and tissues
(does not have a trypomastigote form, which is found in blood)
Which two parasites cause elephantiasis?
- Wulchereria bancrofti*
- Brugia malayi*
What are the risk factors for Echinococcosis infection?
Contact with dog feces
What is the difference between an intermediate host and a definitive host of a parasite?
Intermediate = harbors the larval (asexual) stage of the parasite
Definitive = harbors the adult (sexual) stage of the parasite
Which of the following is a zoonotic infection?
A. Chagas disease
B. Cutaneous leishmaniasis
C. Amoebiasis
D. Trichomoniasis
A. Chagas disese
Other animals are hosts; humans are an incidental host
What are the clinical manifestations of Trypanosoma cruzi infection?
Chagas’ Disease
- Acute phase (high parasitemia)
- Periorbital edema (Romana’s sign)
- Fever
- Anorexia
- Hepatomegaly
- Lymphadenopathy
- Death (occasionally, mostly in infants)
- Chronic phase (undetectable parasitemia)
- Cardiomyopathy
- Megaesophagus
- Megacolon
- (everything is swollen)
Why might doxycycline be used to treat Wuchererica bancrofti, Brugia malayi, and Onchocerca volvulus, but not Loa loa?
Wuchererica bancrofti, Brugia malayi, and Onchocerca volvulus harbor Wolbachia bacteria
Doxycycline can kill Wolbachia to reduce the severe, damaging immune response that the bacteria has when it is released from its dying worm host
Loa loa do not harbor Wolbachia
Which filarial nematode cannot be infected by wolbachia?
Loa loa
(Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus cannot replicate without wolbachia endosymbiont)
Leishmania is in which protozoal group?
Which disease is it associated with?
Flagellates (hemoflagellate)
Leishmaniasis
How is Malayan filariasis transmitted to humans?
Which life cycle stages are present? Where?
Mosquitos transmit Brugia malayi larvae to humans
The adult worm lives in the lymphatic vessels and nodes
Sheathed microfilariae live in the bloodstream
(Causes elephantiasis)
This egg belongs to which helminth?
Schistosoma japonicum
No spine
List 4 filarial parasites
- Wuchereria bancrofti*
- Brugia malayi*
- Loa loa*
- Onchocerca volvulus*
Where is each Schistosoma species endemic?
- S. mansoni = Africa, Middle East, South America, Carribean
- S. japonicum = Far East
- S. haematobium = Africa (esp. Nile River Valley)
Ancylostoma duodenale is a…
Old world hookworm (intestinal nematode)
Which of the following is a human pathogen?
A. Iodamoeba butschlii
B. Entamoeba coli
C .Entamoeba dispar
D. Entamoeba histolytica
E. Dientamoeba fragilis
D. Entamoeba histolytica
What is Wolbachia?
Why is it significant to parasitic infection?
Wolbachia is a gram-negative, intracellular bacteria
The bacteria are endosymbionts of arthropods and some filarial nematodes; without the bacteria, the nematodes cannot reproduce. Contribute significantly to virulence
- Found in…
- Wuchereria bancrofti
- Brugia malayi
- Onchocerca volvulus
- Not found in…
- Loa loa
(like Rickettsiae)
Which component of our immune system is most important in fighting helminths?
Eosinophils: Antibody-dependent cellular cytotoxicity
Which insect carries the parasite that causes African Sleeping Sickness?
Which parasite?
Tsetse fly
Trypanosoma brucei
What is the correct sequence for malaria parasite development?
A. Merozoite→Trophozoite→Schizont→Sporozoite→Merozoite
B. Sporozoite→Merozoite→Trophozoite→Schizont→Merozoite
C. Trophozoite→Merozoite→Schizont→Sporozoite→Merozoite
B. Sporozoite→Merozoite→Trophozoite→Schizont→Merozoite
A patient’s blood sample is positive for Trypanosoma bruci.
Which form/stage of its lifecycle is the protozoa in?
Trypanosoma; this is the stage that is found in the blood
Failure to eradiate which tissue reservoir of hypnozoites following infection with P. vivax may result in resurgence of infection
What are the possible clinical presentations of infection by an Echinococcus spp?
Tissue infection
- Cystic hydatid disease/cystic echinococcosis
- Echinococcus granulosis
- Most common
- Cyst in liver (most common), lung, other organs
- Slow growing
- Usually asymptomatic (unless very large)
- Rupture may cause anaphylactic reaction
- Alveolar hydatid disease (rare)
- Echinococcus mutilocularis
What are the 3 major types of Leishmaniasis and their causative parasites?
Which organisms carry the parasite?
Leishmaniasis is caused by Leishmania spp, and the vector is the sandfly (phlebotamine)
- Visceral leishmaniasis
- L. donovani
- L. donovani chagasi
- Cutaneous leishmaniasis
- Old World
- L. major
- L. tropica
- L. ethiopia
- New World
- L. mexicana
- L. braziliensis
- Old World
- Mucocutaneous leishmaniasis
- L. braziliensis
What organisms cause malaria?
Plasmodium spp
- Plasmodium falciparum
- Plasmodium vivax
- Plasmodium ovale
- Plasmodium malariae
- Plasmodium knowlesi
What is the clinical presentation of cutaneous leishmaniasis?
Chronic, non-healing ulcer
- Usually resolves within several months; leaves a scar
- Can relapse
- Therapy helps prevent relapse
What is the clinical presentation of Trypanosoma brucei infection?
African Sleeping Sickness
Bite: non-pustular, painful, itchy chancre 1-3 weeks after bite
- East African = Acute
- T. brucei rhodensiense
- Abrupt onset of fever
- Headache
- Occipital lymphadenopathy (Winterbottom’s sign)
- West African
- T. brucei gambiense
- Subacute, chronic meningoencephalitis
- Subtle personality changes
- Somnolence
- Coma
- Death
Which form of Schistosoma is likely to be found floating in fresh water?
Cercariae - can infect humans
Miracida - newly hatched, can infect snails
What is a paratenic host of a parasite?
A host that harbors a form of the parasite that does not undergo further development
Which Plasmodium spp. have a “latent liver phase?”
What does this mean?
Plasmodium ovale and Plasmodium vivax
Latent liver phase = they can turn into hypnozoites and lay dormant in the liver, causing relapse years after the initial infection
Strongyloides stercoralis is a…
Intestinal nematode
Which of the following protozoal infections may be transmitted via blood transfusion?
A. Entamoeba histolytica
B. Cryptosporidium parvum
C. Trichomonas vaginalis
D. Trypanosoma cruzi
E. Giardia lamblia
D. Trypanosoma cruzi; the only one that can be found in the blood
Entamoeba hystolitica, cryptosporidium parvum, and giardia lamblia are transmitted fecal-orally; reservoir in soil
Trichomonas vaginalis is in the genital tract
How is Chagas’ disease diagnosed?
Serology
What is the principal complication of infection with Ancylostoma duodenale?
Anemia
Failure to eradiate which tissue reservoir of hypnozoites following infection with P. vivax may result in resurgence of infection?
A. Lung
B. Brain
C. Spleen
D. Liver
E. Bone marrow
D. Liver
P. ovale can also form hypnozoites and lay dormant in the liver.
This is known as the “latent liver phase”
A young woman has just learned she is pregnant and wishes to minimize the risk of congenital disease in her baby. Which of the following will NOT reduce that risk?
A. Avoid travel to Lyme endemic regions
B. Have her spouse clean the cat litter box
C. Consume meat only when cooked “well done”
D. Wash her hands after changing diapers at the day care center where she works
A. Avoid travel to Lyme endemic regions
Lyme disease is not a TORCH agent
- Spouse cleaning litter box, consuming meat when well done = prevents toxoplasmosis
- Washing hands after diaper change = prevents CMV (High levels in urine)
This picture shows a sample of heart tissue infected with Trypanosoma**.
Which Trypanosoma is this most likely to be?
Which life cycle stage are we looking at?
Trypanosoma cruzi - Chagas’ disease - infects heart tissue to cause cardiomyopathy
This is the amastigote stage that is intracellular or in tisuses.
(Trypomastigotes are found in blood)
Which Schistosoma form infects snails?
Miracida enter snails -> sporocysts replicate in snails -> cercariae are released from snails
Which group of protozoa does the causative agent of malaria fall in?
Sporozoans
Why isn’t Onchocerca volvulus treated wtih diethylcarbamazine, an agent that would kill adult worms and microfilaria?
Killing the adult worms would release the endosymbiont W**olbachia living inside of the worms;
Instead, ivermectin is used to kill only the microfilariae
What does Toxocara cause?
Visceral larva migranes
How is Loiasis transmitted to humans?
Which life cycle stages are present? Where?
Horseflies transmit Loa loa larvae to humans
The adult worm lives in the lymphatic vessels and nodes
Sheathed microfilariae live in the bloodstream
(Causes calabar swelling)
Describe the immune response to a schistosome infection
No response to adults; the worms absorb human antigens
Inflammatory response to eggs (100s-1000s produced daily)
- Delayed-type hypersensitivity reaction
- Granuloma formation
Cestodes are _____worms
Tapeworms
(a type of flat worm)
Describe the pathogenesis that causes the major symptoms of malaria
Anemia
- Plasmodium digests hemoglobin -> RBC lysis
Capillary leak syndrome
- Cytokine release (TNF, IFN-gamma, IL-1) causes diffuse endothelial activation and inflammation
- This may cause diffuse intravascular coagulation and capillary leak syndrome
End-organ dysfunction
- Sequestration and endothelial cyto-adherence -> capillary bed occlusion
Jaundice
- Hepatocyte injury
CNS injury
- P. falciparum, P. knowlesi
Which insect carries the parasite that causes Leishmaniasis?
Which parasite?
The sandfly (phlebotamine)
Carries Leishmania spp
Note: Different species are associated with different regions and flavors of disease
Think about the two relevant Trypanosoma species:
What are they?
Which insect carries each one?
Which diseases do they cause?
-
Trypanosoma cruzi
- Reduviid bug (Triatomine, “Kissing bug”)
- Causes Chagas’ disease
-
Trypanosoma brucei
- Tsetse fly
- Causes African Sleeping Sickness
What are the features of a chronic infection with Schistosoma mansoni?
Portal hypertension
This egg belongs to which helminth?
Schistosoma haematobium
Terminal spine
Trichuris trichiura is a…
Whipworm (intestinal nematode)
What is the presentation of Taeniasis solium?
If Taeniasis solium proglottids are ingested = tapeworm infection
If Taeniasis solium eggs are ingested = cysticercosis (CNS disease)
This sample from the patient’s blood shows a parasite, identified as a flagellated protozoa
Could this be Leishmania? Why or why not?
This could not be leishmania
Leishmania spp. in humans do not swim around in the blood, as this protozoa is doing; they only infect macrophages in their amastigote form
(amastigote = a-mobile = immobile)
The species shown above is Trypanosoma, in its trypomastigote form
Which form of Trypanosoma spp. exist in the guts of their insect hosts?
Epimastigotes
(In general: epimastigotes and promastigotes are in flies, while amastigotes and trypomastigotes are in humans; not all protozoa take every form)
This egg belongs to which helminth?
Schistosoma mansoni
Lateral spine
Which organism is thought to have inspired the “symbol of medicine?”
How?
The guinea worm
It is extracted from humans by slowly winding it around a wooden peg
A 28-year-old male returns from a safari in Tanzania with fever, headache, muscle and joint pains. On exam he has a large sore on his right arm and enlarged lymph nodes. His blood smear is shown.
Untreated, he is at risk of developing which of the following complications:
A. Severe anemia
B. Meningoencephalitis
C. Cardiomyopathy
D. Megaesophagus
E. Hypersplenism
B. Meningoencephalitis
The patient has African Sleeping Sickness, cause
(Note: Chagas disease can result in cardiomyopathy, megaesophagus, and hypersplenism, effectively ruling all three of those out; additionally, Chagas is endemic to South America, not Africa)
If a test question asks you about the life cycle stage of a hemoflagellate protozoa, what is a good rule of thumb to use?
- In flies:
- Epimastigote (replicative)
- Promastigote (infective)
- In humans:
- Amastigote (immobile, in macrophages or tissues)
- Trypomastigote (mobile, in bloodstream)
Based on this image, which organism is the definitive host of malaria?
Which is the intermediate?
Why?
Mosquitos are the definitive hosts
Humans are the intermediate hosts
Adult sexual stage occurs in mosquitos
77-year-old man presents with fever and chills 2 weeks after returning from Brazil. What is the cause of his illness?
His blood smear is shown below:
A. Trypanosoma cruzi
B. Trypanosoma brucei gambiense
C. Plasmodium falciparum
D. Plasmodium vivax
D. Plasmodium vivax
Not Trypanosoma; Trypanosoma are not intracellular (and T. brucei is only found in Africa)
Not P. falciparum; P. falciparum causes RBCs to get sticky and clump when it turns into trophozoites (due to action of PfEMP1), and these cells are not clumped
