EN
The epidemiology of the PRRS is much more complicated in comparison to other viral diseases, relating to its spread and persistence of the virus, which is a marked characteristic. For this reason the immunological status was evaluated in different groups of animals. Herds were located in different regions of Poland, with large, medium and small populations of pigs. The evaluation of the titres of antibodies against-PRRS virus were carried out in 48 herds located in selected regions of Poland (in 2 voivodships from regions of large pig populations, in 4 voivodships from regions of medium and in 4 voivodships from regions of small pig populations). A total of 1515 pigs were submitted for the study. In regions of large pig populations 26 herds were tested. In 19 herds (73%) antibodies of anti-PRRS virus were detected. In 3 herds (11%) a stable inactive immunological status was indicated and in 16 herds (62%) an unstable immunological status was indicated. In 7 herds (27%) antibodies of anti-PRRS virus were not observed. In regions of medium pig population 11 herds were tested. In 6 herds (73%) antibodies of anti-PRRS virus were detected. In 1 herd (10%) a stable inactive immunological status was indicated and in 5 herds (45%) an unstable immunological status was indicated. In 5 herds (45%) antibodies of anti-PRRS virus were not observed. In regions of small pig populations 11 herds were also tested (1 herd was not classified). In 5 herds (50%) antibodies of anti-PRRS virus were detected. In 1 herd (10%) a stable inactive immunological status was indicated and in 4 herds (40%) an unstable immunological status was indicated. In regions of small pig populations there was the highest percentage (50%) of herds that were free from the PRRS virus (5 herds).