Pennsylvania Animal Diagnostic Laboratory System
PADLS Conferences Spring 2001 19. PRRSV
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Five three-week-old pigs with depression, dysorexia and mild diarrhea, from a herd in Delaware with endemic Porcine Reproductive and Respiratory Syndrome arterivirus infection, were submitted to the Large Animal Pathology Laboratory of New Bolton Center for examination. Gross lesions included bronchopneumonia and fibrinous pleuritis with thoracic and pericardial effusion. Histological lesions were bronchopneumonia with abundant necrotic debris and 3 out of 5 pigs has perivascular moderate to severe lymphocytic meningoencephalitis. Abundant PRRSV antigen (indirect peroxidase immunohistochemistry) was identified within the cytoplasm of pulmonary macrophages and pneumocytes and necrotic intra-alveolar debris. Small quantities of PRRSV were also detected within the epithelial cells and macrophages of thymus and tonsils and macrophages of spleen. We identified PRRSV within the capillary endothelium of cerebral vessels and in a few perivascular glial cells. Mycoplasma hyorhinis was isolated from pooled lung samples, and Streptococcus suis was cultured from the lungs of 2 of the piglets. PRRSV was isolated and identified.

PRRSV causes reproductive disorders, including hypofertility and abortion, systemic infection and pneumonia in pigs. Encephalitis is rarely reported and, except for one manuscript (Rossow K. et al., Vet Rec 144(16): 444-8, 1999), lesions are generally mild. In our cases lesions were prominent and PRRSV was detected in large quantities, especially in the lung. Most likely, infection occurred or in utero or following parturition and bacteria played a role in the pneumonia. This is the second report of neurovirulent PRRSV in pigs. If uncontrolled, PRRSV will continue to induce prominent economic losses.

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