TDK conference 2020

Actinobacillus pleuropneumoniae is a facultative pathogenic bacterium, it is widespread worldwide, and causes severe economic losses. It is the agent of porcine haemorrhagic-necrotizing pneumonia and fibrinous pleuritis. The mortality in acute cases is high, while the reduced weight gain, prolonged feeding and costs of medicines decrease the profitability in the chronic form of the disease. A. pleuropneumoniae strains are classified into 2 biotypes and 18 serotypes based on their polysaccharide capsule antigens. Capsule antigens are virulence factors but also play an important role in the immunity.

One of the main ways to control the disease is vaccination of pig herds. Most of the vaccines provide serotype-specific immunity. Therefore, the effective protection requires the continuous monitoring of serotypes of A. pleuropneumoniae strains.

Our study focused on the serological examination of two A. pleuropneumoniae strains from Denmark and Canada, which were not typeable by PCR. We produced hyperimmune sera against both A. pleuropneumoniae strains in 2-2 domestic rabbits. Then we performed passive hemagglutination test, testing all the current 18 A. pleuropneumoniae type strains and the two field strains with all the 18 type sera and the newly produced ones.

As the result of our study, the strain from Canada did not react with any of the hyperimmune sera we produced, only smaller cross-reactions were observed against some heterologous antigens. Presumably, the gene encoding the capsular antigen was not expressed. The sera produced against the Danish strain reacted with the homologous antigen in a titre of 1: 5120, but showed the same strength of reaction with the serum produced against of serotype 1, whereas the strain of the A. pleuropneumoniae serotype 1 did not react with of the hyperimmune serum what was produced against the Danish strains. Further studies are needed to determine whether this one-way cross-reaction means a new serotype.