Genomic and immunoinformatic characterization of canine adenovirus type 1 in parvovirus-infected dogs: A comprehensive study from northeast India.

Canine adenovirus type 1 (CAdV-1), the causative agent of infectious canine hepatitis (ICH), a fatal disease affecting domestic and wild canids, yet its prevalence and molecular characteristics remain underexplored in India's north eastern region (NER). This study presents the first comprehensive genomic and immunoinformatic analysis of CAdV-1 in dogs in the region. Out of 208 canine parvovirus type-2 (CPV-2) positive fecal samples, 36 (17.30%) tested positive for CAdV-1 by PCR. Of the 36 positive samples, 25 samples were sequenced. Deduced amino acid analysis revealed notable amino acid mutations, including Asn127Asp, His129Arg, Trp148Ser, Leu201Pro, Thr206Met and Gly215Glu. Sequence analysis of the 25 field samples revealed distinct regional clustering consistent with regional viral evolution. In terms of relatedness to global strains, the NER isolates showed highest similarity to Asian and European canid and wildlife-origin isolates with 96% to 100% amino acid homology. Selection pressure analysis revealed predominantly purifying selection. aBSREL and Contrast-FEL identified a few codons potentially experiencing weak or episodic positive selection, likely reflecting host immune adaptation. GARD analysis ruled out evidence of recombination. Immunoinformatic prediction identified B-cell epitope, "NKTTTEATIITY ISMTFLLVSLTLFLNLVTLTL," in most CAdV-1 sequences making it a suitable candidate for future vaccine development. The MHC-I binding peptide "LTFPNVLITLNNKY" (positions 83-96) demonstrated a strong affinity for the canine allele, suggesting its potential for triggering cytotoxic T-cell responses. These findings shed new light on the molecular epidemiology of CAdV-1 in the NER and highlight the critical need for multi-pathogen screening, molecular surveillance at wildlife - livestock interfaces, and future whole-genome studies to explicate viral evolution, host interactions, immune evasion, and regional strain diversity.