Toxoplasma gondii infection in pigs: serological, parasitological and molecular findings as meat safety parameters | Инфекција паразитом Toxoplasma gondii код свиња : серолошки, паразитолошки и молекуларни налази као параметри безбедности меса

Due to its worldwide distribution, the widest range of intermediate hosts and its ability to parasitize virtually any nucleated cell, T. gondii is regarded as one of the most successful parasites of animals and humans. Immunocompetent individuals rarely suffer from clinical toxoplasmosis, while in immunocompromised individuals infection with T. gondii can have severe, even lethal, consequences. In pregnant women, infection during pregnancy can result in abortion or birth of congenitally infected children. Undercooked meat of infected animals, particularly pigs, represents an important source of human infection. In Serbia, several seroepizootiological studies have been conducted since the 60s, confirming the existence of T. gondii-specific antibodies in pigs. Viable cysts have been isolated from the blood of seropositive pigs as well as from the brain and the heart of pigs of unknown serological status. However, this was the first study to investigate the existence of correlation between the presence of T. gondii-specific IgG antibodies in pig sera and viable cysts in their edible tissues. For this purpose, a total of 200 pigs raised in different management systems (commercial farms, households and free-range systems) were investigated for the presence of anti-T. gondii antibodies. Tissues of seropositive, as well as of some seronegative pigs, were then examined for the presence of tissue cysts, using bioassay (BO) and/or molecular methods (qPCR). T. gondii–specific antibodies were detected in a total of 21.5% of pigs, which may be considered a moderately high finding compared to other European countries. The seroprevalence was higher in free-range pigs (66.7%) than in farm pigs (17.8%) and backyard pigs (16.3%), while no difference was observed between the latter two categories. A total of 59 pigs were examined for the presence of T. gondii tissue cysts using at least one of the two available methods (BO, qPCR) and the parasite was detected in 19 animals. Viable cysts were recovered from 12 out of the 19 samples, which is 6% of all examined pigs. All viable parasites but one originated from seropositive animals; nevertheless, no correlation between specific antibody titre and isolation rate was observed. For genotyping purposes, 18 out of the 19 cyst-positive samples, were investigated by restriction fragment length polimorfism analysis based on nested PCR (Mn-PCR-RFLP), using six genetic markers (alt. SAG2, BTUB, GRA6, C22-8, PK1 and Apico). Typing was successful in a total of nine isolates: two isolates were identified as type III and seven as type II. These results are the first data regarding the population structure of T. gondii in domestic pigs in Serbia and are in accordance with previous findings of type II and III in sheep, pigeons and horses. To conclude, detection of T. gondii-specific antibodies in pigs from different management systems and demonstration of viable cysts in their tissues confirm the significance of pork as a potential source of human T. gondii infection. High seroprevalence as well as the isolation rate observed in traditionally raised “mangulica” pigs suggest that special attention should be paid to applying appropriate tissue cysts inactivation methods during the production and preparation of their meat. Absence of correlation between specific antibody titer and T. gondii isolation rate observed in this study, together with the detection of viable cysts in tissues of seronegative animals, lead to the conclusion that serological status of a pig is not a reliable measure of the safety of its meat for human consumption. Identification of pig isolates as type II and type III represents an important contribution to the understanding of the T. gondii population structure in meat-producing animals in Serbia.