GI Parasites Flashcards
True or false: GI parasite infecions typically cause chronic disease.
true - or at least have the potnetial to cause chronic disease
True or false: people with GI parasite infections are almost always symptomatic.
false - often asymptomatic
What transmission route is an essential part of parasite infections regardless of if they’re water-borne, zoonotic or live in soil?
fecal transmission
so inadequate disposal/treatment of human waste, inadequate treatment of drinking water, lack of handwashing, lack of food washing
What makes protozoa differ from helminths?
protozoa are unicellular eukoaryotes while helminths are multicellular eukaryotes
What are the three main protozoan GI parasites? At least in the US….
Giardia - GIardiasis
Crytoposidium - Crypto
Entameoba - Amebiasis
In general, what stage of the protoxoa is ingested for disease to occur?
cysts or oocysts
True or flase: protozoan infections are typically very serious and require drugs
false - usually not serious for healthy indviduals
most don’t need treatment with drugs and some are asymptomatic
What are the common symptoms of the protozoan infections?
stomach cramps, gas, nausea, fluid loss with diarrhea lasting over a week
often noted upon return from travel
Is the onset for a protoxoan infection sudden or gradual?
gradual - the indubation period can be weeks
What is the most common protozoal infection in the US?
giardia lamblia
although it’s 10-fold more common in developing countries
How long do you have symptoms with giardia?
1-2 weeks or more - but it may seem to resolve and then come back so it can be longer
What is the mechanism of symptoms for giardia? Is it invasive?
just the presence of the parasite causes a loss of epithelial absorptive surface area
other factors may play a role but we really don’t understand it well
doesn’t invade
Describe the life stages of giardia?
- The trophozoites (swimming protozoa) in the gut will attach to the mucosal lining (but don’t penetrate)
- generate cysts in the gut
- cysts release in fecal matter (as are trophozoites, but they die)
- cysts survive in the water until ingested by a new host
So what will you see in the stool to confirm a diagnosis of giardia?
cysts
What are the useful symptoms for diagnosis of giardia?
the diarrhea is foul smelling, greasy and tend to float because it causes malabsorption of fat
issue with fat soluble vitamins
flatulence
How can you prevent getting giardia?
filter the water in areas wehre the cysts are likely - boil basically
doesn’t have to be contaminated by human sewage because wildlife like beavers can deposit the cysts
Where s cryptosporidium parvum a problem?
in populated areas wehre a sanitation system fails - like a pool or waterpark when the chlorination fails or a city after a big storm compromises its water supply
True or false: crypto can be considered an opportunistic infection.
true - HIV and immunocompomised individuals are at higher risk and can develop a chronic diarrhea which is potentially fatal
Describe the symptoms of cryptosporidium parvum.
it’s watery, non-bloody stool lasting for 1-2 weeks or up to a month
fever sometimes
Is cryptosporidium parvum invasive?
slightly - it disrupts the epithelial microvilli and slides into the surface of the host. but doesn’t go very far, which is why the diarrhea is non-bloody
Describe the life cycle of cryptosporidium parvum.
- Sporozoite invade the epithelial surface
- generates oocysts
- oocysts released in feces
- picked up by another human in water
So what will give you a positive idagnosis of crypto?
the oocysts found in feces
What subclass is cryptosporidium a part of ?
the coccidia subclass of apicomplexan protist
What are two other coccidia that cause human GI infections?
cystoisospora belli
Cyclospora cayetanensis
Where is Entamoeba histolytica most prevalent?
not very common in the US - more prevalent int ropical and subtropical climates
What disease is caused by entamoeba histolytica?
Amebiasis, AKA amebic dysentery, amebic liver abscesses
What percentage of individuals infected with entamoeba will become ill?
only 10-20%
Of the US population, which group is most vulnerable for entamoeba?
male homosexuals
What are the symptoms of amebiasis? What can it do to the liver?
- BLOODY MUCUS-FILLED diarrhea
- relatively mild symptoms
- can invade the liver and form an abscess
What do you have to differentiate amebiasis from?
bacillary dysentery
What will give you a positive diagnosis of entamoeba?
cysts in the stool samples
Describe the life cycle of entamoeba?
the cyst is ingested in water
- cysts hatch to trophozoites in the gut
- trophozoites migrate form small intestine to alrge itnestine
- Invade from there - can go to liver
- patient will excrete cysts in the feces
What lobe of the liver is usually affected by an absces sin amebic hepatitis?
right -usually just a single abscess
On histology, what would you expect the appearance of entamoeba to be?
you’ll eitehr be able to see the round disc of th enuclus or you’ll see phagocytosed red blood cells inside
What 7 drugs do we use as anti-protoxoals?
metronidazole tinidazole Iodoquino; Nitazoxanide Paromomycin Trimethroprim:Sulfamethoxazole
Metronidazole and TInidazole are both from what class of drugs?
nitroimidazoles
What is the spectrum for metronidazole and tinidazole?
giardiasis, amebic dysenteri, also anaerobic GI bacteria
NOT crypto
Are metronidazole and tinidazole tissue or luminal antiparasitics?
tissue antiparasitis - the oral dose is almost completely absorbed with high bioavailability so it has low concentrations in the intestinal lumen
What is the mechanism of action for metronidazole?
Toxic metabolites will generate free radicals to induce DNA strand breakage
What are the side effects of metronidazole?
disulfiram reaction with alcohol
nausea, diarrhea, metallic taste
will disturb normal GI flora (but used to treat c diff)
What is the spectrum for nitazoxanide?
Giradiasis and ctyprosporidosis
but healthy hosts are typically not treated and it’s not all that effective in immunocompromised
Is nitazoxanide a luminal or tissue antiparasitic?
luminal - it’s only moderately absorbed (33%)
What is the mechanism of action for iodoquinol?
unknown
What’s the toxicity for iodoquinol?
loss of visual acuity
also use with caution in patients with thyroid diasease
Is iodoquinol a luminal or tissue antiparasitis?
luminal - only 10% of the drug is absorbed so it works locally on the protozoa including the cysts within the GI lumen
What is the spectrum for iodoquinol? I.e. what parasite do we use it for most?
amebic dysentery
What is the mechanism of action for Paromomycin?
it’s an aminoglycoside, so it targets the 30S ribosomal subunit to inhibit protein synthesis
What are the side effects of paromomycin?
diarrhea, issues with intestinal flora
Is paromomycin luminal or tissue?
luminal
What is the spectrum for paromomycin?
most intestinal protozoa, but it’s only partially effective against cryptosporidium
Why is the luminal vs. tissue consideration ipmortant for entamoeba?
it invades and destroys tissue, so you need both a luminal amebicide and a tissue amebicide to treat effectively
What broad spectrum antimicrobial can be used for the other special ones like cystoisospora and cyclospora?
TMP-SMX
What are the toxic effects of TMP-SMX?
it’s well tolerated in general
crosses BBB so can have neurological side effects. High potential to interfere with normal GI flora, can’t give in pregnancy
What are the three groups of worms?
nematodes (roundworms)
cestodes (tapeworms)
Trematodes (flukes)
What are the 5 nematodes we need to know?
Enterobius (pinworms) Ascaris (giant roundworms) Strongyloides Ancylostoma/Necator (hookworm( Tirchuris (whip worm)
What is Enterobius vermicularis also known as?
pinworm
Enterobius wins the prize for what?
most common helminth infectin in the US
What is the prevalence of enterobisu infection?
u to 50% in children, caregivers of infected children and institutionalized idnividausl
What are the symptoms of enterobius infection?
perianal pruritis is a dead giveaway
can also present with insomnia, abdominal pain, anorexia, irritability
rarely peritoneal granulomas and volvovaginitis
What stage of the enterobius is ingested to start an infection?
the pinworm egg
which can remain viable on surfaces for 2-3 weeks
Describe the lifecycle of the pinworm.
- eggs ingested
- laveae hatch in the small itnestine
- adult worms mature in the gut and head to the anus to lay their eggs on the surface at night
maturation takes several months
How can you diagnose pin worm?
appearance of worms 2-3 hours after the patient is asleep - can do the scotch tape method to pick up eggs
sample from under fingernails
note that eggs will likely not be found in the stool sample
What are the two soil-transmitted roundworms that enter via skin penetration?
necator
strongyloides
What two soil-transmitted roundworms get intot he body via egg ingestion?
ascaris
trichuris
For Necator hookworm, what will be present in the stool?
egg
For strongolides, what will be in the stool?
larvae
Describe the life cycle of necator and strongolides? they’re basically the same….
- larvae in soil
- penetrate through the skin of bare feet
- enter the circulatory system and enter lungs
- cough them up to the throac and then swallow them
- get down into the gut where it establishes infection and matures into adult worm
What will be the first presenting sign of a necator infection?
a pruritic papular, erythematous rash
Why do hookworms cause iron-deficiency anemia as the main symptom?
they suck blood! about 1/4 a ml of blood per day per worm
What are the symptoms of strongolides?
stomach and GI complaints
dry cough and throat irriation
itchy red rash on feet - recurrent along the thighs and buttocks
what makes strongolides different from necator ,expecially with immunosuppressed individuals?
autoinfection is possible with strongolides
What’s another name for Trichuris trichiura?
whipworm or trichuriasis
How can you make a positive diagnosis for trichuris trichiura?
eggs in feces will have a characteristic barrel-shaped appearance
What happens to the hands of people with trichuris trichiura?
finger clubbing - the best indicator of severity of infection
How does trichuris cause iron deficiency anemia?
different from necator….it just causes chronic bloody diarrhea
What is the technical name for the giant roundworms?
ascaris lumbricoides - disease is ascariasis
What proportion of tropical populations is infected with ascaris?
about half!
Typically ascaris infections as asymptomatic - maybe just abdominal discomfort. What’s the complication in severe cases?
intestinal blockages that require surgery
What will be seen on histology due to eosinophil breakdown in an ascaris infection?
charcot-;eyden crystals
How can you diagnose ascaris? besides imaging in the blockage cases….
eggs with thick shells in the stool
What is the general mechanism of drugs that affect roundwrms?
they target the worm’s motor activity or reactions that generate metabolic energy for motion
if you inhibit their ability to get around, they’ll be more likely to be pooped out
What are the two broad spectrum benzimidazole drugs used for roundworms and tapeworks?
albendazole and mebendazole
Albendazole and mebendazole have limited oral absorption - which is better if you’re targeting tissue-migrating larvae?
albendazole - it’s slightly better absorbed than mebendazole
What is the mechanism of action for albendazole and mebendazole?
bind to parasite beta tubulin and inhibit the formtaion of microtubules such that the helminths can’t move and die after several days
What are the toxic effects of albendazole and mebendazole?
systemic toxic affects on the liver and bone marrow (rare)
abdominal pain, nausea, dizziness, headache
teratogenis in pregnanc rates
safe for use in children!
What are the two chlinergic antihelminthics?
pyrantel pamoate and levamisole
How does levamisole work?
it selectively opens a trstricted subgroup of nematode acetlcholine receptor ion chnannels in their nerve and muscle
this causes depolarization with an entry of calcium to trigger spastic muscle contractions, thus making the worm unable to maintain its location and gets swept away
What are the side effects of pyrantel pamoate and levamizole?
nausea, vomiting diarrhea
What is the spectrum for pyrantel pamoate and levamisole?
only roundworms
What is the mechanism of action for ivermectin?
It binds to glutamate-gated chloride channels in invertebrat nerve and muscle cells , causing deactivation of the channel
this means they can’t move and the worm dies of starvation
What are the toxic effects of ivermectin?
it’s generally well tolerated
itching, swollen lymph nodes and rarely dizziness
can get an inflammatory reaction due to the dead worms
What is the spectrum of action for ivermectin?
the type of channel affected is only in nematodes like ascaris, strongyloides and onchocerca
Tapeworms are segmentted. What is one section called?
a proglottid
What’s the latin name for the typicla human tapeworm, beef tapeworm or pork tapeworm?
Taenia
What’s the latin name for the fish tapeworm - the one that can reach 30 feet long?
Diphyllobothrium
What tape worm can cause disease of the liver, lungs, brain and other organs with hidadid cysts?
echinococcus
How do you get taenia or diphyllobothrium?
improprtly cooked meat or fish
for fish tapeworm - you ingest larvae in the musculature of fish
What is the main symptoms of diphyllobothrium/fish tapeworm?
you get the standard intestinal problems and then megaloblastic anemia due to comeptition for B12 in the ileum
What will the stool contain in a diphyllobothrium infection?
proglottins and/or eggs
An infection of taenia can sometimes have the cysterci migrating to muscle, brain or other tissue. What’s this called?
Cysticercosis (can cause seizures if in the brain)
Describe the lifecycle of Echinococcosis.
- Dog is the definitive host
- Dog will have eggs in feces
- We ingest the eggs4. the Oncosphere hatches and penetrates the intestinal lining
- Enters the circulation and travels to other organs
- Grow into cysts within those organs
What will the symptoms of echinococcosis be?
depending on where hte cysts form - upper abdominal pain or chest pain
Again, what drugs can we use against tapeworms that would also work against round worms?
benzimidazoles like albendazole and mebendazole
What other drug besides the benzimidazoles will work against tape worms?
praziquantel
What is the mechanism of praziquantel?
increases permeability of the parasite to divalent cations, leading to C2+ entry and contraction of worm musculature
What are the side effects of praziquantel?
well tolerated
dizziness and nausea
What other class of helminths will praziquantel work on?
trematodes or flukes
It’s the only one FOR TREMATODES!!!
What is the main trematode affecting humans?
schistosoma (mansoni or japonicum)
disease is schistosomiasis
What are the two main forms of schixtosomiasis?
intestinal and urogenital
True or false - we are not a definitive host for schistosoma.
false - we are definitive
What is the intemediate host for schisotoma mansoni?
snails - especially biomphalaria glabrata
What causes the general symptoms of schistosomiasis?
our immune response to the egg stage of the schistosoma in our bodies
they can be lodged in the intestine or bladder causing inflammation an dscarring
Why is this such a big public health issue among children?
kids can get repeated infections which causes organ damage, anemia, malnutrition and learning difficulties
What are the symptoms of schistosomiasis?
Rash or itchy skin within days of infection
fever, chills, cough and muscle aches in 1-2 months
chronic form with abdominal pain, hepatomegaly, bloody stool, hematuria or problems passing urine
increases risk fo bladder cancer
Describe the life cycle of schistosoma.
- eggs passed in urine or stool
- enters the water supply
- snails pick up the eggs
- eggs turn to sporocysts
- sporocysts released into water
- humans pick up the sporocysts while they swim
- sporocyst enters circulatory system
- travels to lungs, then heart, then liver and matures to adult worm
adult worm can live for many years
Why might you need to give a second dose of praziquantel after an initial treatment 2-3 months prior?
praziquantel has low efficacy against immature worms, so sometimes you have to wait for the last ones to grow up
note this is also why they usually wait 3 months after an acute infection to treat - if they do it before, it won’t work
What class of drugs can be used to relieve the symptoms of acute schistosomiasis?
corticosteroids - help control the allergic reaction to the eggs
