Prevalence of Actinobacillus pleuropneumoniae serovars in Poland

Porcine pleuropneumonia, caused by Actinobacillus pleuropneumoniae (App), is worldwide in its distribution and has caused severe economic losses in most pig-rearing countries. Epidemiologically, serotyping is the gold standard method, with App being classified into 15 different serovars based on the presence of surface carbohydrates, principally of the capsule. Variances in the virulence between serotypes have been reported. Virulence is strongly correlated with the production and secretion of different exotoxins ApxI, ApxII and ApxIII. Knowledge of the serotypes which exist within a particular region or country is therefore important. The aim of this study was to investigate the prevalence of App serotypes in Poland.

A total of 153 App strains isolated from 2011 to 2015 from diseased pigs, suffering from severe respiratory signs, were tested. No more than one isolate of App from the same farm was included in this study. Antisera against the reference strains (kindly supplied by Dr Gottschalk, University of Montreal) were prepared using a modification of the technique described by Mittal et al. Isolates were serotyped using a slide agglutination method.

All strains were NAD-dependent (biovar1). Among 153 strains of App, the reactions with rabbit polyclonal antisera were found as follow: antiserum 2 – 26.1 %, 4 – 8.5%, 5 – 7.8 %, 9 – 6.5 %, 6 – 5.9 %, 7 – 3.9 %, 11 – 2.6 %, 8 and 3 (1.3 % each), 1 and 15 (0.65 % each). Cross-reactions with antisera 4 and 7; 1, and 9 and 11, have been reported in 11.8% and 2.6%, respectively. Approximately 20 % of the isolates were untypable using the slide agglutination technique due to cross-reactions with several antisera (2-8).

Serotype 2 was the most common detected. Serotypes 4, 5, 9, 6 of App were isolated relatively frequently. Serotypes 7, 11, 8, 3, 1 and 15 occurred rarely. Classical immunological-based methods have limitations, in particular, well known, cross-reactivity between serovars 4 and 7, between serovars 1, 9 and 11, as noted in current studies. A large number of non-typable isolates (20%) requires the use of other techniques in the future like capsulation gene – based PCR.

Previous report (Tarasiuk, 1997) have recorded the presence of serotypes 9, 6, 4 and 2 with the domination of 9 serotype in Poland.

Disclosure of Interest: None Declared.