Co-Infection of Porcine Circovirus 2 (PCV-2) with Synergistic Infections and their Multisystemic Pathological Consequences

The present study was aimed at screening synergistic infections in Porcine circovirus 2 (PCV2) infected pigs. Among the 80 cases studied, 18 were PCV2 positive and these positive samples were subsequently analysed for possible viral and bacterial co-infections. Further investigation revealed three PCV2 cases co-infected with classical swine fever virus (CSFV) infection, two cases with porcine reproductive and respiratory syndrome virus (PRRSV) and one with porcine parvovirus (PPV) infections. The present case describes the multisystemic pathological events observed in a case of concurrent infection with PCV2, CSFV, Escherichia coli (E. coli) and Pasteurella spp. in a six-month-old male cross-bred pig presented for necropsy to the Department of Veterinary Pathology, College of Veterinary and Animal Sciences, Mannuthy, Thrissur, Kerala, from an organised farm in Thrissur, Kerala. The animal had a history of weakness, reduced appetite, fever and diarrhoea. Necropsy revealed petechial to ecchymotic skin haemorrhages, congested and consolidated lungs, endocardial haemorrhages, splenic infarction, gastric ulcers, catarrhal enteritis and congested kidneys with petechiation. Microscopically, broncho-interstitial pneumonia, vascular changes like congestion, haemorrhages and thrombus formation together with degenerative and necrotic changes were evident in the lungs, heart, ton-sil, testes, spleen, lymph nodes, kidney, skin and liver. Lymphoid depletion and histiocytic replacement were the characteristic lesions observed in lymphoid organs. Molecular detection of PCV2 by polymerase chain reaction (PCR) targeting the ORF-2 gene revealed an amplicon size of 481 bp. Similarly, in the case of CSFV, nested reverse transcription polymerase chain reaction (RT-nPCR) targeting the E2 gene showed 271 bp sized amplicons and PCR for Pasteurella spp. expressed amplification of a 560 bp fragment of the rpoB gene. Sequencing was done to confirm the identity of the viruses and phylogenetic analysis for PCV2 was also performed. Bacteriological examination, culturing of tissue samples and biochemical tests confirmed the presence of E. coli as well. Such occurrences of combined infections warrant strict prophylactic and scientific management practices in swine rearing.