Parasites II

Question 1

what are the 3 lumen-dwelling protists? What is a significant virulence attribute? What is unique/notable about their lifecycle?

Answer 1

entamoeba histolytica, giardia lamblia, trichomonas vaginals

none requie an intemrediate vector for life cycle or transmission

Question 2

What is the disease transmission of entamoeba histolytica and life cycle? What are the host(s)

Answer 2

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)

Question 3

How do you diagnose entamoeba histolytica?

Answer 3

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)

Question 4

What are the disease manifestations of enntamoeba histolytica?

Answer 4

• 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.

Question 5

How do you treat entamoeba histolytica? how does this drug work? contraindications?

Answer 5

metronidazole (flagyl)
indtruduces alkyl radicals into biologically active molecs
contraindicated during pregnancy, esp. 1st trimester –> teratogen
tinidazole also OK

Question 6

What factors contribute to pathogenesis of E. histolytica- ie. what chemicals are secreted?

Answer 6

amebopore, which is involved in lysis of host cell bilayers

proteases and collagenases

Question 7

How does E. histolytica target its victim cells for lysis, biochemically? How does this relate to immunity?

Answer 7

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

Question 8

What are two complications of amebic ulcer of the colon?

Answer 8

1. leakage into the peritoneum with bacterial infection

2. spread to the liver and abscess formation

Question 9

Why are asymmptomatic carriers important to E. histolytica?

Answer 9

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.

Question 10

What is the role of the immune system in E. histolytica infection, and what is the relationship between immunity and infection?

Answer 10

• 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.

Question 11

What is one distinguishing finding of E. histolytica on stool culture examination?

Answer 11

cellular morphology and presence of ingested erythrocytes

Question 12

What part of the body is infected with giardia lamblia? How is it transmitted and who’s at risk?

Answer 12

upper 25% of GI tract

transmitted by fecal-oral route; wild animals/pets; oral/anal sexual contact, nursing homes/preschools

Question 13

What are the symptoms of girardia lamblia infection?

Answer 13

WATERY diarrhea

damage less extensive than that seen with entamoeba.

Question 14

How do you diagnose and treat giardia lamblia?

Answer 14

1. stool exam for cysts
2. entero-test: gelatin capusule on a string is swallowed for overnight GI incubation. then it is retrieved and examined for organisms.
3. biopsy/ duodenal aspirate (very last resort)

Question 15

What is the relationship btw giardia lamblia and the immune system?

Answer 15

surface antigen variation makes it hard for the immune system to clear the infection.

Question 16

What is the treatment for giardia lamblia? Who is qualified to receive treatment?

Answer 16

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

Question 17

How do you prevent giardia lamblia infection?

Answer 17

iodine water purification, but requires relatively high levels of iodine.
boiling of water
good hand washing

Question 18

Are there any other conditions caused by giardia lamblia infection?

Answer 18

carrier states

malabsorption mistaken for lactose intolerance or milk allergy in kids

Question 19

What is unique about trichomonas vaginal life cycle? How is it transmitted?

Answer 19

• only trophozoite form is observed- no cysts

- transmitted by sexual contact; possible but very very rare congenital respiratory transmission

Question 20

What parts of the body are infected in trichomoas vaginals infection? What pathology does it cause? What are the virulence factors?

Answer 20

women- vagina
men- prostate and urethra
damages epithelum by direct contact –> microulcerations
adhesins and proteases are the virulence factors

Question 21

triomonas vaginals infection symptoms

Answer 21

women: soreness, irritation, pelvic/abdominal pain
men: usually asymptomatic
often, purulent yellow discharge observed for both- but sometimes mistaken for candida in women.

Question 22

How do you distinguish between candida and trichomonas vaginalis infections? Any other considerations in diagnosis?

Answer 22

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

Question 23

How do you treat trichomonas vaginalis?

Answer 23

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