Wk4 GI Parasites Flashcards
Three unicellular eukaryotic parasites:
Protozoans
1. Entamoeba
- Giardia
- Cryptosporidium
Life stage of nematodes, Cestodes, and trematodes in mammal host:
Juvenile and adult worms
Giradia mechanism:
Presence of parasite decreases absorptive surface area
diahrrea 1-2 weeks, may resolve then return
Form of Giardia that gets ingested:
cysts
Form of Giardia present in fecal matter:
Trophozoites + cysts
FOUL smelling diarrhea
Flatulence
Greasy stools that float
Giardia
Failed sanitation system (water park, drinking water)
Diarrhea 1-2 weeks –> 30 days
Cryptosporidium parvum
Ingestion of SMALL oocysts
disrupts epithelial microvilli –> envelopes in host cell membrane
impaired absorption, enhanced secretion
watery, frequent, NON-bloody stools
Opportunistic (HIV)
Cryptosporidium parvaum
Cryptosporidium form found in feces:
oocysts
Infectious and damage causing forms of Cryptosporidium:
Sporulated oocysts
Sporozoites
Bloody-MUCUSEY loose stools
can invade liver –> abcess
Dx: cysts in stool
No fever, chills, or pus
Entamoeba histolytica
–> Amebic dysentery (differentiate from Bacillary which HAS fever, chills, and pus)
Location for Entamoeba histolytica:
USA at risk population:
tropics –> poverty areas
homosexual males
Life cycle for Entomoeba histolytica on host:
ingest cysts –> trophozoites in small intestine –> migrate to colon –> cysts and trophozoites in feces
Disease mech for E. histolytica:
hint: “Hitsto–lytica”
tissue lysis
tissue abcess in upper right liver lobe
RUQ pain
fever
weight loss
Amebic hepatitis
TISSUE antiparasitic (completely absorbed)
free-radical forming –> DNA strand breaks
TiniDAZOLE
MetroniDAZOLE
Antiparasitic
intersferes with pyruvate
moderatley absorbed – primarily luminal
less efficacy in immunocompromised with Crypto
Nitazoxanide
luminal antiparasitic (amebicide)
loss of visual acuity
careful with thyroid disease
Iodoquinol
Luminal antiparasitic
Aminoglycoside (30s subunit)
Side Fx: diarrhea
Paromomycin
Systemic side effects of aminoglycosides not a problem with paromomycin?
ototoxicity
nephrotoxicity
**not absorbed
Most common helminth (worm) infx in the US:
Enterobius vermicularis
*a round worm
perianal pruritis
Enterobius vermicularis
**a round worm
Form of E. vermicularis ingested:
pinworm eggs
**can remain viable on surfaces for 2-3 weeks
Life span from egg to adult Enterobius vermicularis:
1-2 months –> live for 2 months as adult
Where/when do Enterobius vermicularis lay their eggs?
perianal region
at night
**larva can crawl back up for retroinfection
Dx for Enterobius vermicularis:
Scotch tape of anal region looking for eggs in the morning
**NOT likely in stool
Soil transmitted round worm
9-11 mm
eggs in stool
can be in skin and lungs
blood suckers
Necator
Necator americanus/Ancylostoma duodenale
hookworms**
Iron deficiency anemia
Necator
OR
Trichuris trichuria
Recurrent raised red rash along thighs and buttocks
Autoinfection in IC pts
a few mm in size
Strongolides stercoralis
**a round worm
barrel shaped eggs in feces
adults 3-5 CM
finger clubbing
bloody, mucus, watery diarrhea (Fe deficiency anemia)
Trichuris trichiura
**a round worm
Huge worm (15-35 cm)
not common in US
1 BILLION in tropics infected per year
Ascaris
Charcot-Leyden crystals
eggs with THICK shells
Ascaris
Binds parasite B-tubulin (different than host tubulin)
inhibits motor activity and metabolism
Albendazole (better for tissue)
Mebendazole
Cholinergic antihelminth drugs
cause spastic muscle contraction so parasite can be swept away
Pyrantel pamoate
Levamisole
**N/V, diarrhea, poorly absorbed
Binds glutamate gated Cl- channels
worm paralysis and death by starvation
Spectrum: ?
Ivermectin
Nematodes - Ascaris, Strongyloides, Onchocerca
Typical human tape worm:
Taenia
3-10 m length
tapeworm
beef or pork
Taenia
Fish tapeworm
size ?
Diphyllobothrium
HUGE!! up to 30 ft
Tapeworm of liver, lungs, brain
size?
Echinococcus
tiny, a few mm
Morphological difference between round worms and tape worms:
tape worms are SEGMENTED
Competes for B12 in intestine
**maybe after eating uncooked fish
Diphyllobothrium
Stage of Taenia ingested from beef or pork?
cysticerci
–> grows to tapeworm in small intestine
**can become cysticerosis if migrates to muscle, brain or other tissue
Dogs are definitive host
not really GI illness at all
sheep farming
cysts in organs
Echinococcus
Tx for tapeworms that also targets GI roundworms:
MOA?
Benzimidazoles
-Albendazole, Mebendazole
B-tubulin binder
-inhibits motor function and metabolism
Tapeworm drug
increased permiability of parasite –> divalent cations –> contraction of worm musculature
Praziquantel
Cestodes?
tapeworms
Liver involvement
RUQ pain
Entamoeba histolytica
Second to malaria as most devastating parasitic disease:
schistosomiasis
**a fluke
Mechanism of disease for schistosomiasis:
IMMUNE response to eggs
infection –> days –> rash, itching
1-2 months –> F/C, cough, muscle aches
Chronic –> abd pain, HEPATOMEGALY, bloody stool/urine
increased risk of bladder cancer
schistosomiasis
How does Schistosoma infect humans?
lives in snails in water (sporocysts–intermediate host)
free swimming cercariae leave snail and penetrate human skin
get into blood and go to lungs, heart, then liver (thats where they mature)
migrate to bowel and bladder
300 eggs/day to blood, can live 20 years
eggs leave in feces and urine –> back to water for round 2
Swimmers itch
Cercarial dermatitis
Tx for schistosomiasis:
praziquantel
same as tapeworm drug, increases permiability
low efficacy against immature worms
