Virulence markers of Haemophilus parasuis associated with clinical and pathological outcome in the field

Haemophilus parasuis is regularly involved in fibrinous inflammation in pigs, especially relevant for pneumonia, serositis, arthritis, meningitis and pericarditis. As a worst case, SPF herds can suffer from Glässer’s disease after acute outbreaks in naïve animals. However, commensalism seems much more common than primary disease and it is hard to differentiate between strains of high and low virulence. The aim of the present survey was to study associations between molecular markers of Haemophilus parasuis and the virulence of field isolates.

More than 150 strains of Haemophilus parasuis were collected from swine herds in Germany (Lower Saxony and Hesse). The severity of disease levels within herds varied from definite cases of commensalism to cases with specific, high degree clinical and pathological symptoms. Individual pigs were dissected and sampled. Haemophilus parasuis was cultured and serotyped and 17 putative and potential virulence genes were screened by PCR. The virulence genes were selected from capsular genes (capD), autotransporters (vtaA), outer membrane proteins (ompP2, ompP5), fimbriae (pilF), cytholethal distending toxins (cdt), serine protease-like-proteins (espP2) and bacteriophages (gp36).

Individuals and herds varied significantly in their clinical and pathological outcome, both in a qualitative and quantitative manner. Samples revealed a huge range of strains differing in serotypes and virulence gene patterns. There was no association between serotypes and pathology, but three virulence genes were significantly linked with the severity of disease: ompP2, cdt and espP2a. These genes are well known to be crucial in evading the immune system and thus, for survival in the host. Together, they explained more than 30% of total variation in clinical and pathological symptoms (multiple r = 0.55; p< 0,001).

The presented data provide evidence for a significant role of outer membrane protein 2 (ompP2), the cytolethal distending toxin (cdt) and the serine-protease-like-protein 2 (espP2) for the pathogenesis and outcome in Haemophilus parasuis-affected pigs in the field. Further investigations and the inclusion of additional molecular factors are needed to efficiently differentiate between Haemophilus parasuis strains and to improve future diagnostic opportunities.

Disclosure of Interest: None Declared.