Parasitology 3 Flashcards
How is entamoeba histolytica transmitted?
Ingestive- fecal-oral
Direct- anal sex
The majority of chronic asymptomatic amoeba infections are likely due to
Entamoeba dispar
Describe endemic and epidemic causes of amebiasis in the US
Endemic: institutions, anal sex
Epidemic: faulty water purification
Describe the lifecycle of Entamoeba histolytica
Acid resistant cysts are ingested, excystation in distal small intestine
Trophozoites attach to colonic mucin and divide. can penetrate the mucosal layer leading to invasive disease
Resistant cysts form in the large intestine and divide
In amoeba infection, formed stools contain _____ and loose diarrheal stools contain
formed stools: cysts
diarrhea: trophozoites
Trophozoites of entamoeba histolytica can travel to the ______ and form an abscess
liver
Distinguish between asymptomatic, dysentery, and invasive disease with Entamoeba histolytica
carriers: chronic form for months or years, shed millions of cysts/day
dysentery: severe bloody diarrhea, invasion of colonic epithelium, submucosal ulcers
invasive: rare, not always associated with dysentery, formation of liver abscess
Describe any immunity to Entamoeba histolytica
- humoral response in invasive disease
- possibly some acquired immunity in endemic areas
How is amebiasis diagnosed?
Cysts in stool
Trophozoites containing RBCs
Stool antigen, PRC, serology
Correlate to travel history
What is treatment for Entamoeba histolytica
metronidazole or tinidazole for invasive tissue phase
paromomycin for lumenal phase
True or false: like Entamoeba histolytica, Giardia can cause invasive disease
FALSE- luminal only, no invasive disease with Giardia
What is the reservoir for Giardia lamblia?
Wild and domestic animals
How is Giardia transmitted?
fecal-oral
sexual- oral/anal sex
endemic in developing countries, epidemics at day cares, resorts, camping
Describe the lifecycle of giardia
ID as low as 10-100 cysts
Cysts are eaten
Trophozoites excyst in upper small intestine, multiply by binary fission
Encystation in large intestine
Excretion of cysts and trophozoites in the feces but only cysts survive in the environment
Describe specific symptoms of giardia
explosive diarrhea with flatus, belching, cramps
malabsorption- don’t absorb fat, lactose, vitamin A, B12
Describe any immunity to giardia
re-infection is possible
humoral response seen
some resistance in endemic areas
How is giardia diagnosed?
stool examination, presence of cysts, ELISA antigen test on stool sample
What treatment is used for giardia?
metronidazole, tinidazole, nitazoxanide
List three genera within the family Apicomplexan
Cryptosporidium
Plasmodium
Toxoplasma
Apicomplexan parasites are____________ parasites, which allows them to remain hidden from immune response and thus the immune system is poorly able to control them
obligate intracellular
Felines are the definitive host of ________
toxoplasma gondii
Ticks are the definitive host of __________
babesia microti
Mosquitoes are the definitive host of _______
Plasmodium species
What is the definitive host of cryptosporidium hominis?
Humans
Does Cryptosporidium cause invasive disease?
No. Luminal only
How is cryptosporidium transmitted?
Fecal-oral route
What is the reservoir of cryptosporidium?
wild animals, livestock
Cryptosporidium parasites are unique in that they are located _____ but ______, which explains why drugs for other apicomplexan species are not effective against cryptosporidium
intracellular but extra-cytoplasmic
_______ plays a major role in AIDS wasting syndrome
Cryptosporidium
Shedding of cryptosporidium oocytes is highest in the _____ phase but continues after symptoms resolve
acute
Describe any immunity to cryptosporidium
The fact that it is a self limiting illness suggests that there may be some immunity
Cryptosporidium is usually a self limiting illness with 1-2 weeks of symptoms but people who are ________ may fail to resolve the infection
immunocompromised
What is appropriate treatment for cryptosporidium?
oral rehydration, especially in immunocompromised
restore immune function with HAART for HIV infected
short course of nitazoxanide for immunocompetent/ longer course if immunocompromised, not clear how effective this is
What organism is suspected if microscopy shows “cup in saucer” shaped cysts in the stool?
Cryptosporidium
What is the location of infection with toxoplasma gondii?
tissue and blood
What are intermediate hosts of toxoplasma gondii?
any warm blooded animal
How is toxoplasma gondii transmitted?
ingestive: fecal-oral, undercooked meat
transplacental: congenital infection
Congenital infection with toxoplasma gondii is most likely if maternal _______ infection during prengancy
primary- less risk if mother is previously seropositive, has strong IgG immunity
Reactivation of a __________ is thought to play a role in toxoplasma infection in immune compromised individuals
latent reservoir
Pregnant women should be advised to avoid the following activities to prevent congenital toxoplasmosis:
eat poorly cooked meat
change litter box
garden
Initial infection with toxoplasma is often ________
asymptomatic
Toxoplasma infection is rapidly controlled with ______ mediated immunity leading to a life long state of latent infection with sub-clinical reactivation
cell
Toxoplasma _______ is a major cause of death in AIDS
encephalitis
In utero infection with toxoplasma is most serious ______ in pregnancy
early- can cause miscarriage in first trimester
third trimester effects are often milder, can include retardation, birth defects
Mild cases of congenital toxoplasmosis can develop ________ in later life
chorioretinitis
Treatment for toxoplasmosis always involves ______ therapy
combination
List some medication regiments for treatment of toxoplasma
pyrimethamine/sulfonamide
pyrimethamine/clindamycin if sulfa allergy
prophylactic trimethoprim (TMP)/sulfa if CD4 count <100 for sulfa allergy, prophylactic dapsone or atovaquone/ pyrimethamine
spiramycin if pregnant- pyrimethamine is a tetratogen
How is toxoplasma diagnosed?
Serology, indirect immunofluorescence
Interpret the following serology findings for toxoplasma: Seropositive for IgG and seropositive for IgM, High IgG avidity
Previously infected with toxoplasma, at least 12 weeks prior but less than 2 years prior
Interpret the following serology findings for toxoplasma: Seropositive for IgG and seropositive for IgM, Low IgG avidity
Infected with toxoplasma, likely recent infection, sample again in three weeks
Interpret the following serology findings for toxoplasma: Seronegative for IgG
Not previously infected
Interpret the following serology findings for toxoplasma: Seropositive for IgG, seronegative for IgM
Infected for > 6 months, chronic infection
Toxoplasma shows up on brain MRI as __________ lesions
ring enhancing
If there is only one ring enhancing lesion on MRI, brain biopsy may be done to evaluate for ________
lymphoma
