The aim of this study was biological and molecular characterization of classical swine fever (CSF) challenge virus from India. CSF challenge virus maintained at Division of Biological standardization was experimentally infected to two seronegative piglets. The biological characterization was done by clinical sign and symptoms along with postmortem findings. For molecular characterization 5'-nontranslated region, E2 and NS5B regions were amplified by reverse transcription polymerase chain reaction and sequenced. The sequences were compared with that of reference strains and the local field isolates to establish a phylogenetic relation. The virus produced symptoms of acute disease in the piglets with typical post-mortem lesions. Phylogenetic analysis of the three regions showed that the current Indian CSF Challenge virus is having maximum similarity with the BresciaX strain (USA) and Madhya Pradesh isolate (India) and is belonging to subgroup 1.2 under Group 1. Based on biological and molecular characterization of CSF challenge virus from India is described as a highly virulent virus belonging to subgroup 1.2 under Group 1 along with some field isolates from India and Brescia strain.

Classical Swine Fever (CSF) is one of the most important viral infections affecting swine. In the present study, the complete genome of the cell culture-adapted lapinized Indian Classical Swine Fever virus (CSFV) was cloned into the pBR322 vector using an improved method. The viral RNA was amplified by RT-LA PCR into two overlapping fragments of ~ 6.5 kb and 5.8 kb sizes, and cloned separately into the pTZ57R/T vector. To generate CSFV full-length cDNA, the segments were fused utilising a restriction endonuclease region located within the overlapping region. The complete genome was then cloned into the pBR322 vector and designated as pBR/T7-CSFV. The recombinant plasmid was confirmed by PCR, restriction enzyme analysis, and nucleotide sequencing. The full-length cDNA backbone of CSFV can serve as a reverse genetics model with the T7 promoter and can be used for creating recombinant viruses and for developing a DIVA strategy for CSFV. This study describes a modified method for full-length amplification of an Indian CSFV isolate and cloning it into the pBR322 vector. Graphical Abstract