Parasitology: Protozoans

Answer 1

Giardiasis: Giardia lamblia aka G. intestinalis, G. duodenale

• Epidemiology: Mostly in developing countries, less so in N. America, Europe, and Australia, at risk include immunosuppressed (AIDS Pt), sewage workers, crowded institutions, travelers
• Reservoir/hosts: beaver and dogs
• Transmission: fecal-oral
• Features: trophozoite not infective, fecal-oral parasites.
• Sx: pale loose stools (foul smelling; fatty), frequent, ab distention & pain, flatulence (offensive), wt. loss, sulphorous belching
• Dx: Stool microscopy (cysts/trophs in severe diarrhea), ELISA, immunofluorescent test, string test (indirect, used if other test results -ve, capsule filled w corn flour and usually get dramatic improvement)
• Rx: metronidazole,

Answer 2

Cryptosporidium parvum

• Epidemiology: lake areas of the world
• Reservoir host: cows, dogs
• Vector
• Features: zoonotic, oocyst in greenish diarrhea
• thin-walled oocysts reinvade gut -> autoinfection so DO NOT slow down with anti-diarrhea meds, sporozoites innoculates host
• Sx: vary according to immunocompetent or immunosuppresed
  
  • Immunocompetent: diarrhea (explosive, watery, greenish-brown), frequent (2 to 10/day). fever vomiting, anorexia, ab discomfort,
  • Immunocompromised: large vol. diarrhea (5 L/day), malabsorption, wt loss, villous atrophy
• Dx: modified Ziehl-Neelsen stain for oocysts in stool, ELISA, immunoflourescent test (IFAT)
• Rx: none except supportive therapy
• Control:

Answer 3

Amoebiasis: Entamoeba histolytica

• Epidemiology
• Vector: lives free form in water?
• Features: Trophozoites (RBC’s invasive form)
• Sx: varies depending on Intestinal or Invasive type
• Intestinal: 95% aymptomatic, diarrhea inconsistent w gradual onset, no fever, no flatulence, ab pain, frequency
• Invasive: bloody diarrhoea, pathogenic invasive strains, may form amoebic abscesses in: liver (majority), brain, skin, lungs, orbit, spleeb, and genitals, Amoebic Liver Abscesses (ALA; fever, tender liver, epigastric pain, hepatomegaly),
• Dx: cysts in stool (smear or float), ELISA, direct aspiration of abscess, US, X-Ray, CT, MRI (indirect)
• Rx: vary depending on Intestinal or Amoebic Abscesses
• Intestinal: Metronidazole followed by Paromomycin
• Amoebic Abscesses: chemo, metro for small cycsts, US-guided drainage for large
• Control: Hygience, boiling or filtering water, cooking veggies, proper sanitation, safe pipes, no night soil fertilisation

Answer 4

Toxoplasmosis: T. gondii

• Epidemiology: world-wide, at risk include undercooked meat eaters, cat owners, butchers, vets, children who eat soil or unwashed veggies
• Host: definitive hosts are cats however b/c they produce the oocysts, but also pigs, goats, chickens, goat, sheep, pigeons,
• Features: Zoonotic, vertical transmission
  
  • Bradyzoites: clusters enclosed by an irregular crescent-shaped wall, slow-growing, no inflammatory changes
  • Oocysts
  • Tachyzoites: motile forms of coccidians that form tissue cysts, infect leucocytes, infection predilection sites are Brain & Eye (fetus)
• Sx:
  
  • immunocompetent individuals: asymptomatic
  • fetal infection: hydrocephalus, chorioretinitis
• Dx: imaging (CT, MRI), biopsy
• Rx: ventriculoperitoneal shunt
• Control: test cats of pregnant owners for T. gondi Ab (infection), maternal testing & spiramycin (prophylactic)