Parasites II Flashcards
what are the 3 lumen-dwelling protists? What is a significant virulence attribute? What is unique/notable about their lifecycle?
entamoeba histolytica, giardia lamblia, trichomonas vaginals
none requie an intemrediate vector for life cycle or transmission
What is the disease transmission of entamoeba histolytica and life cycle? What are the host(s)
fecal/oral route
humans are the principle hosts
cyst is the infectious form that can resist gut enzymes and stringent pH conditions
converts to trophozoite form in the colon
trophozoite is motile, replicative, and disease-causing but is not infectious except via sexual contact (rare)
How do you diagnose entamoeba histolytica?
trophozoites or round cysts in the stool; trophozoites only seen in the stool during active infection
in highly invasive cases, antibody titer is a better test (stool numbers are diminished)
What are the disease manifestations of enntamoeba histolytica?
- colitis and/or dysentery
- BLOODY diarrhea
- abscesses, esp. in liver. this happens with species that have acquired resistance to complement lysis.
- ameboma- annular granulomatous lesion of the bowel.
How do you treat entamoeba histolytica? how does this drug work? contraindications?
metronidazole (flagyl)
indtruduces alkyl radicals into biologically active molecs
contraindicated during pregnancy, esp. 1st trimester –> teratogen
tinidazole also OK
What factors contribute to pathogenesis of E. histolytica- ie. what chemicals are secreted?
amebopore, which is involved in lysis of host cell bilayers
proteases and collagenases
How does E. histolytica target its victim cells for lysis, biochemically? How does this relate to immunity?
lysis requires cell-cell contact
adhesion medated by lectin on the pathogen binding galactos and N acetyl galactosamine on the host cell. then, the two cells are in close enough proximity for the release of lytic factors.
Lectan can also confer resistance to complement via molecular mimicry- structurally similar to complement regulatory proteins that prevent the C5-9 complex from forming. This is the basis for complement resistance
What are two complications of amebic ulcer of the colon?
- leakage into the peritoneum with bacterial infection
2. spread to the liver and abscess formation
Why are asymmptomatic carriers important to E. histolytica?
only the healthy carriers can produce enough cysts to spread the infection to other hosts. healthy hosts don’t develop immunity to E. histolytica in the gut.
What is the role of the immune system in E. histolytica infection, and what is the relationship between immunity and infection?
- serum and secretory abs are produced but are NOT protective
- cell mediated immunity is necessary- activated macrophoges are toxic. But, during advanced chronic disease, E. histolytica specifically suppresses cell-mediated immunity.
What is one distinguishing finding of E. histolytica on stool culture examination?
cellular morphology and presence of ingested erythrocytes
What part of the body is infected with giardia lamblia? How is it transmitted and who’s at risk?
upper 25% of GI tract
transmitted by fecal-oral route; wild animals/pets; oral/anal sexual contact, nursing homes/preschools
What are the symptoms of girardia lamblia infection?
WATERY diarrhea
damage less extensive than that seen with entamoeba.
How do you diagnose and treat giardia lamblia?
- stool exam for cysts
- entero-test: gelatin capusule on a string is swallowed for overnight GI incubation. then it is retrieved and examined for organisms.
- biopsy/ duodenal aspirate (very last resort)
What is the relationship btw giardia lamblia and the immune system?
surface antigen variation makes it hard for the immune system to clear the infection.
What is the treatment for giardia lamblia? Who is qualified to receive treatment?
treatment should be initiated in any pt with disease symptoms and positive organism ID.
treat with antibiotics and metronidazole, tinidazole, or nitazoxanid.
metronidazole and tinidazole introduce alkyl radicals that disrupt activity of biomolecs
nitazoxanid interferes with anaerobic energy metab in parasitic protists
How do you prevent giardia lamblia infection?
iodine water purification, but requires relatively high levels of iodine.
boiling of water
good hand washing
Are there any other conditions caused by giardia lamblia infection?
carrier states
malabsorption mistaken for lactose intolerance or milk allergy in kids
What is unique about trichomonas vaginal life cycle? How is it transmitted?
- only trophozoite form is observed- no cysts
- transmitted by sexual contact; possible but very very rare congenital respiratory transmission
What parts of the body are infected in trichomoas vaginals infection? What pathology does it cause? What are the virulence factors?
women- vagina
men- prostate and urethra
damages epithelum by direct contact –> microulcerations
adhesins and proteases are the virulence factors
triomonas vaginals infection symptoms
women: soreness, irritation, pelvic/abdominal pain
men: usually asymptomatic
often, purulent yellow discharge observed for both- but sometimes mistaken for candida in women.
How do you distinguish between candida and trichomonas vaginalis infections? Any other considerations in diagnosis?
trichomonas vaginals have characteristic pear shape and are motile on a wet mount.
make sure to avoid fecal contamination- feces often contains non-pathogenic organisms that resemble trichomonas vaginalis
negtive wet mount doesn’t necessarily rule out infection- secretions can be cultured
How do you treat trichomonas vaginalis?
metronidazole or tinidazole. DON’T give to preg. women
make sure you also treat sex partner(s) to avoid recurrent infection
advise on safer sex techniques
