PROTOZOA—life cycles Protozoa Transmitted ;Trophozoites (merozoites, tachyzoites) — active, feeding, via Food (and Water) dividing (+ bradyzoites) ;Cysts — inert transmission form PHR 250 (exception: Toxoplasma) ;Gamonts → zygote → oöcyst (sporozoites) Giardia lamblia Giardiasis (= duodenalis = intestinalis) ;Leading protozoan cause of foodborne and waterborne disease in US ;CDC, ’98−’02: 3 foodborne outbreaks, 119 cases; ’03−’04: 2 waterborne outbreaks, 14 cases ;Spheroid cysts 9–12 µm long Giardia cyst Giardiasis 1 Giardia trophozoite Giardia lamblia ;Incubation 7–10 days; characteristic diarrhea from noninvasive colonization of upper small intestine may persist for weeks if untreated; asymptomatic infections very common. ;Reservoirs: humans, beavers, cattle, and other animals. Giardia lamblia vehicles ;Unfiltered surface water Cryptosporidium parvum (Giardia is fairly resistant to ;Oöcysts from humans, cattle, chlorine) other domestic & wild species ;Drinking water recontaminated (human-specific species: “C. with sewage hominis”) ;Fruits, vegetables, salads, and ;Small (4–6 µm), tough, chlorine- other foods subject to direct or indirect fecal contamination resistant Cryptosporidium parvum Cryptosporidium parvum ;Outbreaks from apple juice ;Largest outbreak of waterborne (cider) 1993 & 1996, and raw disease in history (Milwaukee, milk and a few other food 1993, ca. 403,000 cases, but only vehicles one waterborne U.S. outbreak ;CDC (’98–’02): 4 outreaks, 130 during ’03–’04 cases ;FoodNet (2005): ~8850 cases 2 Cryptosporidium C. parvum, C. hominis hominis ;Incubation ~1 week, profuse diarrhea usually <30 days (shedding 2–6 months); intracellular parasitism; treatment is rehydration. C. parvum oocyst C. parvum excysting Cryptosporidium parvum or C. parvum sporozoites C. hominis 3 C. parvum or C. hominis C. parvum or C. hominis ;Cryptosporidiosis is ;Concern for cryptosporidiosis diagnostic of AIDS in (especially waterborne) is HIV-positive persons & evoking stringent measures in will generally persist the U.S. and will have a (with intermittent significant impact on symptoms) for life. agriculture involving ruminants. Entamœba histolytica Entamœba histolytica ;Once a frequent cause of ;Causes amebic dysentery, waterborne disease in the sometimes abscesses of liver US, now fairly rare here or other organs (trophozoites ;Continues to be a very are invasive). significant threat in the ;Human-specific; transmitted poorer countries. via fecally contaminated water or food. Entamœba histolytica Entamœba histolytica 4 Entamœba histolytica Entamœba histolytica Toxoplasma gondii Toxoplasma gondii ;Outbreaks (acute, foodborne) rare ;CAST: ~2090 cases, 42 deaths, $2.6 billion/yr (×½?) from congenital blindness, hydrocephalus, retardation T. gondii life cycle Toxoplasma gondii Cat: ;Cats are definitive hosts, usually definitive host infected by eating infected birds External or rodents; oöcysts (not environment immediately infective) in cat Intermediate feces for up to 3 weeks hosts contaminate animal feed, garden vegetables, other foods, water. 5 T. gondii oocyst Toxoplasma gondii T. gondii tissue cyst Toxoplasma gondii ;Tissue cysts (bag of bradyzoites) in pork, mutton, beef — killed by cooking or irradiation; freezing does not eliminate them completely. Toxoplasma gondii Cyclospora cayetanensis ;Tachyzoites may encyst in ;Human-specific; delayed various tissues (often CNS in maturation (days to weeks humans); cellular immune under favorable conditions) of response causes encystation as oöcysts in feces makes person- bradyzoites; tissue cysts well to-person transmission unlikely. tolerated in humans but may be ;Fairly common in parts of Latin reactivated if immunity is later America and Asia impaired. 6 Cyclospora cayetanensis Cyclospora cayetanensis ;Rare in U.S., but caused an ;CDC (‘98–’02): 9 outbreaks, extensive (nationwide + Canada) 325 cases outbreak in May–June of 1996, ;FoodNet (2005): ~450 cases eventually attributed to raspberries imported from Guatemala; again in 1997; embargoed in U.S. (but not Canada) in 1998; back in 1999? Cyclospora cayetanensis Cyclospora cayetanensis Summary Cyclospora cayetanensis ;Limited look at foodborne ;Presently, there are just four protozoa Guatemalan farms that may be ;Five agents discussed; three permitted to export raspberries species (Cryptosporidium to the U.S., contingent on fecal hominis, Cyclospora cayetanensis testing of the farm workers. & Entamœba histolytica) are ;No positive fecal tests had human-specific & transmitted by resulted, at last report. a fecal-oral route. 7 Summary ;Others all transmitted zoonotically at least some of the time, either via infected animal feces or tissue ;Human feces also important sources of Cryptosporidium hominis (& parvum?) oöcysts and Giardia lamblia cysts that may be transmitted to humans via water or food. 8.