Serotype-specific monitoring of Actinobacillus pleuropneumoniae in Thuringian pig farms

Actinobacillus pleuropneumoniae (APP) is a major cause of porcine respiratory tract infections where morbidity and lethality are influenced by the serotype and the virulence of the bacterium. Thuringian pig farms were tested for APP antibodies as part of a serologic monitoring programme. By retrospective evaluation of the testing results from one year, the aim of this study was to investigate the occurrence of APP serotypes in Thuringian pig farms and to evaluate whether serotype specific monitoring provides added value compared with non-specific screening. In the year 2012 blood samples of about 30 pigs per farm were collected on two occasions approximately six months apart and were tested for APP antibodies. Commercial ELISA kits were used for the non-specific as well as the serotype-specific screening. A total of 3509 samples were tested with 1551 positive and 1852 negative results in the non-specific screening. The positive test results originated from 76 out of 81 farms. Antibodies against the serotype groups 4-7 and 3-6-8 occurred in more than 85 % of these farms. Antibodies against serotype 5 were found in only a quarter of the farms with a median of 5 % non-negative samples per farm. If antibodies against the serotype group 4-7 were detected, a noticeably higher proportion of pigs (37 %) showed positive or suspicious test results. The frequent occurrence of antibodies against APP in Thuringia as detected by the non-specific screening test is primarily due to the high proportion of the low virulent serotype groups 3-6-8 and 4-7. The more virulent serotypes 2 and 5 were detected less frequently. A serotype specific testing of virulent serotypes, in addition to the non-specific screening, can be recommended, and contributes to a better insight into the APP situation of pig farms and a more justified assessment of APP's role in the complex causality of porcine respiratory tract infections.