Serological behaviour study of Actinobacillus pleuropneumoniae (App) in commercial swine herds from the central region of Chile

Abstract

In Chile, there was only one existing study on App. This study was designed to determine the maternal immunity duration, the age of seroconversion and the apparent and true prevalence in animals from 7 swine commercial herds. 60 samples were taken per herd and divided into 10 serum samples from animals of 4, 6,10,14,18and21 weeks of age, which were analyzed by ELISA®. Out of the 420 samples, 134 were positive with 112 of them belonging to pigs under 10 weeks of age while only 22 were from animals over 10 weeks of age, which seroconverted presumably due to a natural infection. Regarding maternal immunity duration it was found that around the 10^th week of age the animals lose their colostrum antibodies. In seroconversion, from the 18^th week of age animals with their own circulating antibodies begun to appear. Two out of the 7 herds did not seroconvert after the maternal immunity drop, but another two presented a seroconversion over 50% at 18^th week. The apparent prevalence was 10.48 %, meanwhile the true prevalence calculated by two statistical methods was 9.6% (CI: 7.6% -11.7%) and 10.68% respectively. Thus it was proved that the prevalence in the analyzed herds is similar to that found in USA, presumably because of type of production systems and serotypes that are present in both countries. On the other hand, although most of the herds seroconverted immediately after the maternal immunity drop, different serological patterns were observed among them.