Experimental modes of Caryospora bigenetica (Apicomplexa: Eimeriidae) infection in swine and the effects of temperature and salinity on parasite infectivity in porcine tissue.

Four crossbred pigs (Sus scrofa) were inoculated orally with Caryospora bigenetica oocysts derived from snake and mouse feces, and with C. bigenetica infected mouse tissue. One pig also was given i.m. injections of methylprednisolone acetate. All four pigs displayed clinical signs including erythema, edema, and lethargy. Caryocysts were observed histologically in numerous tissues including ear, tongue, jowl, shoulder, loin, intercostal, ham, hock, and feet. The four pigs each were butchered into six commercial cuts: shoulder, loin, side, ham, hock, and feet. Raw 10 g samples from each cut were bioassayed by pepsin digestion and s.c. inoculation into 12 Swiss-Webster mice (Mus musculus) and 12 cotton rats (Sigmodon hispidus). Seventeen of 24 mice and cotton rats exhibited clinical signs and C. bigenetica tissue infections. Remaining portions of the six commercial cuts were temperature or saline treated, and 10 g samples were bioassayed in 16 mice and 12 cotton rats. No clinical sign or tissue infection was observed in these animals. Our study presents evidence that swine can be infected with C. bigenetica by ingesting oocysts present in snake feces or mouse feces (following inoculation of mice with snake-derived oocysts) or by ingesting C. bigenetica infected rodent tissue, that endogenously produced C. bigenetica oocysts are not excreted in the feces of swine, and that C. bigenetica in pork can be rendered noninfective by freezing at -20 degrees C (-4 degrees F) for 21 days, frying at 84 degrees C (183 degrees F) for 17 min, microwaving at 88 degrees C (190 degrees F) for 17 min, grilling at 82 degrees C (180 degrees F) for 48 min, baking at 95 degrees C (203 degrees F) for 230 min, boiling at 100 degrees C (212 degrees F) for 60 min, or by curing at 4 degrees C (39 degrees F) for 20 days.