Pathological insights of Porcine circovirus 2 infection in domestic pigs and molecular characterization of field virus.

Abstract

Porcine circovirus type 2 (PCV2) poses a major threat to global pig industry by causing growth retardation, immunosuppression, co-infections and mortality. PCV2 has high mutation rate and it causes several clinical manifestations and diverse pathological lesions. Therefore, routine disease surveillance is necessary to understand epidemiology, genetic variations and pathology. The study was conducted to investigate occurrence, pathology and genetic diversity of PCV2 circulating among pigs at Bareilly district, Uttar Pradesh, India. Tissue samples (n=130) from pigs were screened using PCR during 2023-2024. Pathological studies were carried out alongwith mutational and structural annotations of ORF2 gene of circulating PCV2. Total 36.15% samples found positive (47/130) for PCV2, with 14.89% showing co-infections with Streptococcus suis and Haemophilus parasuis. There were interstitial and bronchointerstitial pneumonia with inclusion bodies and lymphoid depletion in lymph nodes. PCV2 antigens were detected by IHC in alveolar macrophages, lymphoid follicles of bronchial lymph nodes and tonsils. Apoptotic lymphocytes were demonstrated by TUNEL assay. Two PCV2 isolates were sequenced and compared with an American strain. Phylogenetic analysis of ORF2 gene, revealed that the circulating virus belongs to PCV 2d genotype. Three amino acid substitutions were identified (Y8F, A59T/K, F154Y). Structural modeling based on the bat circovirus capsid protein (PDB ID: 6RPO) showed that these mutations may have altered local polarity but did not alter linear epitope landscape. Study has revealed high occurrence of PCV2 infections in nursing piglets in study area causing diverse pathological lesions and the circulating virus belonged to PCV2d genotype with three amino acid substitutions.