Pathology of Porcine Circovirus 2, Porcine Parvovirus 1 and Streptococcus suis Co-infections in Postweaning Multisystemic Wasting Syndrome in Piglets

Abstract

This study investigated an outbreak of PMWS during April–June, 2025 in an organized pig farm in Bareilly, Uttar Pradesh, India to elucidate the pathological interplay among porcine circovirus 2, porcine parvovirus 1 and Streptococcus suis in piglets. Postweaned piglets (n=10) showing progressive wasting, respiratory distress and followed by death were examined by detailed necropsy, histopathology, PCR and immunohistochemistry. Grossly, piglets were emaciated and showed hydrothorax, fibrinous pleuritis and pericarditis, severe pulmonary lesions, lymphadenopathy, hepatic necrosis, enteritis, nephritis and cerebral congestion, indicating multisystemic involvement. PCR detected PCV2 and PPV1 in all 10 piglets and S. suis in six, while all were negative for PCV3. Microscopically, interstitial and bronchointerstitial pneumonia, marked lymphoid depletion with giant cells formation, myocarditis with chronic fibrinous pericarditis, granulomatous enteritis, interstitial nephritis and hepatic degeneration were prominent. Masson’s trichrome and Brown and Brenn stains demonstrated fibrinous pericarditis and bacterial colonies, respectively. IHC demonstrated PCV2 antigen in bronchial epithelium and lymphoid tissues and PPV1 antigen in intestinal mononuclear cells and myocardium, supporting active viral association in lesion development. The concurrent detection of S. suis in pigs with severe serositis and cardiac lesions exacerbated disease severity. In conclusion, the findings confirmed a multifactorial pathogenic association of PCV2, PPV1 and S. suis in PMWS affected piglets, with coinfections intensifying lesion severity and broadening organ tropism.