Toxoplasma gondii in wild boars and domestic pigs in Sweden

Sammanfattning: Ingestion of undercooked meat is a major risk factor for human toxoplasmosis, a disease caused by the zoonotic protozoan parasite Toxoplasma gondii. Infected pork, mutton and game meat are considered important infection sources in Europe. This thesis aims to describe the epidemiology of T. gondii in two possible key species for human toxoplasmosis in Sweden, namely domestic pigs and wild boars. Approximately half of the wild boars investigated were found to be T. gondii seropositive, and the seroprevalence was dependent on age, geographical region, and year of sampling. In conventional fattening pigs the seroprevalence was estimated to 1%, compared to 8% in pigs raised in organic management systems with pasture access (KRAV). A one-month increase in pasture access was associated with an 80% increase in the odds of being seropositive. This strengthens the hypothesis that pigs become infected via their natural rooting behaviour. The high level of T. gondii infection in wild boars, and the increasing demand for outdoor management systems for pigs, emphasise the need of consumer awareness of proper cooking procedures to prevent infection. Other means to limit meat-borne transmission could include abattoir-based serological screening of pigs to reduce the amount of T. gondii infected meat distributed to consumers. Since it has been suggested that such screening systems could be based on meat-juice serology, a study was conducted to investigate aspects of the sampling and preparation of meat-juice samples. It was found that antibody levels in meat juice varied depending on the muscle used for extraction, and in meat juice obtained from the diaphragm, levels of anti-T. gondii IgG correlated poorly with levels in serum. However, the level of anti-T. gondii IgG in meat juice was associated with the total level of IgG, which could possibly be used to assess if enough antibodies have been distributed to the meat-juice sample for the test result to be reliable. However, implementation of meat-juice serology in risk-management programmes needs to be preceded by further evaluation and standardisation of sampling, extraction, and testing procedures.