Toxoplasmosis in pigs--the last 20 years

Pigs are important to the economy of many countries because they are a source of food for humans. Infected pig meat is a source of Toxoplasma gondii infection for humans and animals in many countries. This parasite also causes mortality in pigs, especially neonatal pigs. Most pigs acquire T. gondii infection postnatally by ingestion of oocysts from contaminated environment or ingestion of infected tissues of animals. Few pigs become infected prenatally by transplacental transmission of the parasite. Raising pigs indoors in confinement has greatly reduced T. gondii infection in pigs but the recent trend of organic farming is likely to increase T. gondii infection in pigs. Recently, feeding goat whey to pigs was found to be a risk factor for T. gondii infection in organically raised pigs. Currently used molecular and histopathological methods are insensitive for the detection of T. gondii in pork because of the low concentration of the parasite in meat destined for human consumption. There is no vaccine to prevent T. gondii infection in pigs but efforts are being continued to develop a non-viable vaccine. In the present paper, information on prevalence, transmission, diagnosis, and control of porcine toxoplasmosis in the last 20 years (since 1988 when last reviewed by this author) is reviewed. Worldwide reports of clinical and asymptomatic infections in pigs are reviewed. Methods to detect T. gondii in pigs are compared. Recent studies on genetic typing of T. gondii strains prevalent in pigs are discussed with respect to epidemiology. Because wild pigs are hunted for food for human consumption prevalence in wild pigs is summarized.