Histopathologic lesions in conventional pigs experimentally infected with Haemophilus parasuis serovar 5.

Objective: In the present study various tissues of pigs were investigated for the presence of histopathologic lesions after an experimental infection with Haemophilus (H.) parasuis serovar 5. Material and methods: Conventional pigs (n = 36) were divided into a control group B (n = 9) and a challenge group A (n = 27), which was infected intratracheally. Pigs that did not die prior to study termination were euthanized on day 14 post inoculation. Postmortem samples of the lung, heart, liver, kidney, spleen, left tarsal joint capsule and brain were collected. Results: All but one pig with detectable histopathologic lesions (n = 11) showed typical macroscopic changes. Histopathologic examination of all tissue samples identified pyelitis (n = 10), synovitis (n = 7) and meningitis (n = 7) and all those animals were euthanized prior to study termination. No histopathologic lesions were found in pigs of the control group. The correlations between pyelitis and meningitis, pyelitis and synovitis and synovitis and meningitis were significant (p < 0.001). No significant correlation could be observed between the histopathologic and the clinical examination of the joints. The investigation of samples from the joints by PCR was not significantly correlated with the observed synovitis. The clinical observation of neurologic signs was significantly correlated with meningitis (p = 0.03). A significant correlation (p < 0.001) could be detected between meningitis and the detection of H. parasuis by PCR in brain samples. Conclusions: H. parasuis constantly causes clinical signs and pathologic lesions as soon as it infects the brain while it can infect the joints without causing histopathologic lesions. Pigs with histopathologic lesions do not always show typical clinical signs. Only few studies described the finding of kidney lesions in pigs with Glasser's disease and this is the first study to describe a pyelitis in pigs experimentally infected with H. parasuis. The observed pyelitis mainly occurred in acute cases.