Ingested Protozoans

Question 1

Entamoeba Histolytica

Answer 1

Infective Cysts occur in formed stool
–typically asymptomatic
Cysts and non-infective trophozoites are found in diarrhea
–individuals with intestinal disease

Transmission
Fecal/Oral, anal sex (direct transmission of trophozoites)
Mechanical vectors for cysts (flies, cockroaches)

Epidemiology
Worldwide
maybe 10% of world population infected

Pathology
Carriers
Asymptomatic: Chronic infection for months or years, massive shedding of cysts

Intestinal amebiasis (dysentery)
Invasion of colonic epithelium, ulceration, abdominal pain, cramping, diarrhea in severe cases numerous bloody stools per day

Extraintestinal amoebiasis
Rare dissemination throughout the body (mostly liver), fever, abscess formation, hepatomegaly

Immunity
Humoral response in invasive disease
Some acquired immunity in endemic areas

Diagnosis
Cysts in stool, cysts and trophozoites in diarrhea
E. histolytica trophozoites contain RBCs
Stool antigens and PCR, serology available
Aspirate of liver abscesses
Travel history

Treatment
Paromomycin for luminal phase, carriers should be treated
Metronidazole or tinidazole, followed by paromomycin for invasive phase

Prevention
Good sanitation and personal hygiene, condoms

Question 2

Giardia Duodenalis

Answer 2

Transmission
Fecal/oral
Direct person-to-person, oral-anal sex
Shedding of cysts may occur in “showers”

Epidemiology
Occurs worldwide, low hygiene areas

Pathology
Asymptomatic (1/2 of infected people) or sudden onset after 2 week incubation period
watery non-bloody diarrhea, abdominal cramps, flatulence, FATTY STOOL
Spontaneous recovery usually within 2 weeks but chronic infection can occur
Maybe have malabsorption syndrome in severe cases

Question 3

Apicomplexan Parasites

Answer 3

Obligate Intracellular stage
Apical organelle for host cell invasion
Complex life cycles alternating between assexual (Schizogony) and sexual reproduction (sporulation)

Sexual cyle in intestinal epithelium of the definitive host

Question 4

Cryptosporidium (Hominis or Parvum)

Answer 4

Transmission
Fecal/Oral, Oral/Anal

Epidemiology
high is developing countries
common secondary infection in AIDS patients

Pathology (Cryptosporidiosis)
Symptoms similar to Giardia, but shorter with greater fluid loss
1-2 weeks incubation, 3 or more times a day watery diarrhea without blood
In AIDS patients, it is most severe profuse diarrhea contributing to AIDS wasting syndrome, failure to resolve

Diagnose
Detection of Oocytes in stool
Immunological detection of antigens in feces

Treatment
No broadly effective therapy available
Oral rehydration, particularly in immunocompromised patients

Prevention
Boil water, chlorination and water filtration, avoid contact with stool

Question 5

Toxoplasma Gondii

Answer 5

Birds and mice to cats

Transmission
Undercooked meat with tissue cysts
Fecal/oral: oocysts from contaminated soil, plants or cat litter box
Transplacental: congenital infection only with primary maternal infection
Blood transfusion or organ transplantation

Epidemiology
Occurs worldwide, associated with undercooked meat and houscats

Pathology/Immunity
Toxoplasmosis (CDC top 5)
Initial infection often asymptomatic (mayb fever, chills)
Rapid control by cell-mediated immunity
life-long latent infection

No control of primary infection, immunocompromised individuals

In utero infection severity depends on time of infection, may cause stillbirth

Diagnosis
Serology, immunofluorescence
PCR
MRI

Treatment
Complex combination treatment essential for immunocompromised or for active chorioretinitis caused by ocular toxoplasmosis

Pyriethamine/sultonamide or clindamycin
Prophylactic trimethoprim
Spiramycin if pregnant

Prevention
Avoidance behavior, eat fully cooked meat and don’t change the litter box or work in the garden (or change the litter box daily)