Ingested Protozoans Flashcards
1
Q
Amebiasis Name Location Transmission Immunity Treatment (lumenal vs invasive phase) Prevention
A
- Entamoeba histolytica
- Location – intestine lumen → invasion of tissues
- Transmission: ingestive (fecal-oral) or direct (anal sex). Poor public sanitation and using human waste as fertilizer. Avg dose is >1000 cysts, but 1 can be infectious.
- Immunity – Humoral responses occur in invasive disease. Reinfection is possible but recurrence of invasive disease is rare. Suggests role for acquired immunity in edemic areas.
- Treatment – Paromomycin for luminal phase. Metronidazole or tinidazole for invasive phase.
- Prevention – hygiene, condoms
2
Q
Amebiasis Life Cycle
A
- Ingest acid-resistant cysts, excyst in distal SI
- Trophozoites attach to colonic mucin and divide. May penetrate mucosal layer → invasive disease, most often associated w/ a liver abscess.
- Cysts form in LI and are shed in feces.
- Formed stool associated w/ cysts
- Diarrheal stool are associated w/ trophozoites. Not orally infective, but can be infective via anal sex.
3
Q
Amebiasis Pathology
A
- Carriers may be asymptomatic for months / years. May have occasional bouts of abdominal pain, flatus, and diarrhea. Shed in stool.
- Dysentery = severe bloody diarrhea. Invades colonic epithelium → flask-shaped submucosal ulcers.
- Invasive amebiasis: spreads through blood to liver → abscess. Occasional spread to brain or lung.
4
Q
Amebiasis Diagnosis (5)
A
- Stool antigen & PCR is best. Distinguishes from E dispar.
- Travel history is essential.
- Cysts in stool. Trophozoites in diarrhea. May see ingested RBCs in trophozoites. Difficult to find.
- Serology – can’t distinguish new from old infection.
- Aspirate liver abscess
5
Q
Giardia lamblia Location Reservoir Transmission Life cycle Diagnosis Treatment (3) Prevention
A
- Location – intestine lumen
- Reservoir – wild / domestic animals (usually asymptomatic)
- Transmission – fecal/oral due to contaminated water (drinking / swimming) or oral-anal sex. Epidemics in daycares and ski resorts.
- Life cycle – Infectious dose is 10-100 cysts, trophozoites excyst / adhere in upper SI via ventral disk (suction cup), multiply, encyst in LI, excreted in feces.
- Diagnosis – cysts in stool, ELISA stool antigen test, DFA (direct fluorescent Ab)
- Treatment – tinidazole or nitazoxanide. Paromomycin if pregnant.
- Prevention – hygiene, safe water (boil, filter, iodine tablets). Typical chlorination of domestic water does NOT eliminate Giardia, Cryptosporidium, or Entamoeba. Boiling and filtration does work.
6
Q
Giardia pathology
A
- Pathology – ranges from asymptomatic to “explosive diarrhea”. Not life threatening.
- Onset is 2 weeks
- Non-bloody diarrhea, flatus, belching, cramps, nausea
- Malabsorption of fat (steatorrhea), lactose, vit A, B12
- Usually self-limited in 1-4 weeks. May be chronic w/ constant shedding in stool.
7
Q
4 diff apicomplexans
General characteristics
A
- Include Cryptosporidium, Cyclospora, Toxoplasma, Plasmodium, etc
- Obligate intracellular parasites.
- Apical organelles are used for host invasion
8
Q
Cryptosporidiosis Name Location Transmission Reservoir Population Immunity Diagnosis Prevention
A
- Cryptosporidium hominis / parvum
- Location – intestine lumen
- Transmission – fecal-oral. May be passed person to person. Associated w/ daycares and recreational water. Nosocomial infections are risk to pxs and providers.
- Reservoir – wild animals / livestock (C parvum; C hominis only in humans)
- Common secondary infection in AIDS pxs
- Immunity – Self-limiting infections suggest role of immunity, but reinfection can occur
- Diagnosis – Cysts examined in stool w/ modified acid-fast (red “cup & saucer” shaped cysts) or stool ELISA / DFA.
- Cysts are very robust; boil water, avoid stool, filter
9
Q
Cryptosporidium Life Cycle
A
- Oocyst ingested, sporozoites invade epithelial cells to reproduce asexually.
- Intracellular, but extracytoplasmic. Found in brush border. Drugs that are active against other apicomplexans are NOT affective against crypto for this reason.
- Thin-walled oocyst initiates autoinfective asexual replication in immunocompromised hosts.
- Thick-walled oocysts are passed in feces in immunocompetent hosts. Shedding of oocysts is highest during acute infection.
10
Q
Cryptosporidium Pathology
A
- May be asymptomatic. More likely to be asymptomatic than Giardia.
- Sxs are similar to Giardia but more acute and w/ greater fluid loss.
- Crypto forms “crypts” in GI tract. Normal mucosa is damaged.
- Profuse watery diarrhea, up to 12L of diarrhea / day in immunocompetent. Up to 25L / day in immunocompromised.
- Immunocompromised pxs have amplification w/in the host. Get more and more fluid loss.
- Major weight loss contributes to AIDS wasting
11
Q
Treatment (3)
A
- Oral rehydration, especially in immunocompromised
- Most pxs don’t need tx. Short course of nitazoxanide for immunocompetent. Longer course for immunocompromised.
- Restore immune system w/ ART for HIV pxs
12
Q
Cyclosporiasis Name Location Transmission Season Immunity Treatment Prevention
A
- Cyclospora cayetanensis
- Location – intestine lumen
- Transmission – ingest from soil. No person to person. Outbreaks include raspberries from Guatemala and fresh produce from Mexico.
- Mainly occurs in summer.
- Immunity: self-limiting infection in immunocompetent pxs suggests role for host immunity, but reinfection can occur. Immunocompromised pxs have more severe disease that does not resolve on its own.
- Treatment – TMP sulfa
- Prevention – sanitation, avoid fresh produce when traveling, boil / filter water (chlorine / iodine does NOT work)
13
Q
Cyclospora Life Cycle
A
- Sporulated oocyst ingested from soil and invades cytoplasm. Diff from cryptosporidium. Tx easily w/ drugs.
- Poop out unsporulated oocyst, which needs environmental time to develop before it can be infectious. Similar to worms. 2-7 days in soil is needed.
14
Q
Cyclospora Pathology
A
- 1 week incubation period. Untreated infection lasts 10-12 weeks followed by relapses.
- May be asymptomatic, especially in endemic regions
- Severe / explosive watery diarrhea, anorexia, weight loss, abdominal pain, nausea, vomiting, myalgia, fever, fatigue
15
Q
Cyclospora Diagnosis
A
- Oocysts in stool, but yield is lower than in cryptosporidium. Cysts are larger than Crypto cysts.
- UV fluorescence microscopy, acid-fast stain, safranini stain
