Parasites Flashcards
1
Q
GI/GU Protozoa
A
- All fecal-oral transmission (except trichomonas)
- Amoebas:
- Entamoeba histolytica - causes bloody diarrhea
- Sporozoans:
- C. parvum
- Cyclospora cayetanesis
- Flagellates:
- Trichomonas vaginalis (sexual transmission)
- Giardia lamblia
- Ciliates:
- Balantidium coli
2
Q
Trichomonas vaginalis
A
- Flagellate ⇒ move w/ flagella
- Can affect both men and women
- Exists only as a trophozoite (growing form; it does not have a cyst form)
3
Q
Giardia lamblia
A
Flagellate ⇒ move w/ flagella
Gives patients cyclic** diarrhea** because Giardia exists in a cyst form that then excysts
4
Q
Entamoeba histolytica
A
- Amoeba ⇒ means it moves w/ pseudopodia
- Although trophozoites found in stool, they are not viable; only cysts are infective
- The cysts are ingested then go through entire life cycle (excystation → trophozoite → multiplication → cystation & trophozoite) in the intestine
- Causes bloody diarrhea
- Trophozoites responsible for pathology via toxin production (toxin not well defined)
- Results in ulceration, hemorrhage and secondary bacterial infection. Although rare, invasion to other tissues (usually liver but sometimes brain, lungs and heart) can occur
- Treat with metronidazole; if invasive add paromamycin
- Cyst – nucleus undergoes 2 mitotic division, so a cysts can have 1, 2, or 4 nuclei (never** **bilobed)
5
Q
Balantidium coli
A
- Ciliate ⇒ moves w/ cilia
- Both cyst and trophozooite have macro and micro nuclei
- macronucleus is typically bi-lobed
- only cysts are infective (life cycle similar to Entamoeba)
- Diarrhea: watery stools with blood and pus; can ulcerate
- Nausea, anorexia
-
Resevoir = pigs
- More common in pigs than people
- Treat with tetracycline (cannot use metronidazole)
6
Q
Cryptosporidium parvum
A
- Sporozoan ⇒ not motile
-
Water-borne and chlorine resistant
- Life cycle: Thick-walled oocyst exits host → Contamination of water and food with oocysts → Ingestion of thick-walled oocyst by new host
- Acid-fast positive
-
Spore-forming
- Extracellular spores
7
Q
C. parvum
A
- Protozoan
- Acid fast
- Fecal-oral transmission from animals to humans
- Ingestion of oocysts (which contain four motile sporozoites) → oocysts release sporozoites in small intestine → sporozoites differentiate into trophozoites and attach to intestinal microvilli (their life cycle occurs within intestinal epithelial cells) → then trophozoites can either undergo:
- Asexual multiplication: trophozoites → schizont → merozoites → trophozoites
- or Sexual reproduction: trophozoites → gametes → zygote → oocysts
- They do not invade!
- Causes severe watery, non-bloody diarrhea in individuals with defective immune systems (e.g., patients with HIGM syndrome or HIV/AIDS) → malnutrition
8
Q
Cyclospora cayetanesis
A
- Sporozoan ⇒ not motile
- Acid-fast positive
-
Spore-former
- Intracellular spores
- Usually food-borne; can be water-borne
- Immature oocyts are excreted and need time to mature outside host before infecting another host
- Infects small intestine – can be found in vacuoles in jejunal epithelial cells, where it causes villus atrophy and crypt hyperplasia
- Oocysts look a lot like Cryptosporidium but are bigger (8-10 um vs 5-7 um) and have only 2, not 4 sporozoites
- Treat with TMP/SMX
9
Q
Protozoa that infect blood and tissue
A
- Sporozoans:
- Apicomplexans
- Plasmodium spp
- Toxoplasma gondii
- Babesia spp
- Apicomplexans
-
Flagellates:
- Naegleria fowlerii
- Trypanosoma brucei
- Trypanosoma cruzi
- Leishmania donovani
10
Q
Apicomplexans
A
- Apicomplexans are asexual
- Commonly undergo binary fission
- Also undergo multiple fission
- Schizont (multiply fissioned) gives rise to merozoitee
-
Merozoite enters host cell and has 2 fates:
- Undergo another round of multiple fission (schizogony/merogony)
- Undergo gametogony and become a gamete
- Sporozoites arise when 2 gametes fuse to form a zygote
11
Q
Naegleria fowlerii
A
- After water-related activities, Naegleria trophozoites enter through your nose and sinuses, migrate to the brain via olfactory nn, penetrate and cause primary amoeba meningoencephalitis in healthy individuals
- Usually fatal
- Cyst form found in water, soil, and plants
- Trophozoites found in CSF. Flagellated forms only occaisionally found in CSF.
- Naegleria (but not Acanthamoeba or Balamuthia) is treated with the anti-fungal Amphotericin B + miconazole instilled directly into the CNS.
- Found in SW US
12
Q
Trypanosoma brucei Gen Cha
A
- Flagellate: Free flagellum and undulating membrane
- Protozoan that causes systemic infection
- Antigenic variation of surface coat (due to gene shuffling) allows protozoan to evade immune response
- Reproduces in blood, lymph, and CSF
-
Sleeping Sickness:
- West African Sleeping Sickness caused by T. b. gambiense and occurs slowly
- East African Sleeping Sickness caused by T. b. rhodesiense and occurs quickly
- CP:
- Enlarged LNs
- Recurring fever
- Then somnolence, coma
13
Q
Trypanosoma brucei Pathobiology
A
Reservoir in animals or humans, transmitted by tsetse fly bite (vector) → Releases protozoan into bloodstream → Divides in blood → triggers host immune response → hard red ulcer at bite site, enlarged LNs, & fever
↓
Gene shuffling → change in surface coat → division in blood → triggers another host immune response → enlarged LNs & fever (cycle recurs every 2 weeks)
↓
After many cycles, protozoa may escape immune response and infect CNS → encephalitis, meningitis → somnolence (sleeping sickness), coma
14
Q
Trypanosoma brucei Dx & Tx
A
- Dx:
- Flagellated protozoan in blood, LN, and/or CSF
- Tx:
- Before CNS infection: suramin (drug does not cross BBB)
- With CNS infection:
- T. b. gambiense: eflornithine
- T. b. rhodesiense: melarsoprol
- Treat with pentamidine– very toxic – treat before in CNS or becomes very difficult to cure
15
Q
Typanosoma cruzi
A
- Many animals serve as reservoirs
- Kissing bug: triatomine bugs (transmit Trypomastigotes in their feces)
-
Amastigotes live within macrophages & can be released to differentiate into trypomastigotes
- Can be dormant for 20 or more years
- Trypomastigotes infect RBCs and are released following lysis
- Chagas can be acute, chronic or asymptomatic
- Romana’s sign – swelling at site of bug bite – usually one side of face, periorbital swelling
- In children often causes acute CNS disease accompanied by fever, chills, malaise, myalgia, and fatigue
- In all infected: hepatosplenomegaly, myocarditis, enlargement of esophogus and colon as a result of destruction of nerve cells (Auerbach plexus)
- Treatable before cardiac involvement
- South America
