Characterization of classical swine fever virus responsible for 2018-2023 outbreaks in Brazil

Abstract Classical swine fever (CSF) remains endemic in the non-free zone (NFZ) of Brazil, posing a persistent threat to the country’s swine industry. Understanding the characteristics and the pathogenesis of endemic CSF virus (CSFV) in the NFZ is crucial for developing effective control and eradication strategies. This study provides a comprehensive molecular and pathological characterization of CSFV strains responsible for outbreaks in the northeastern states of Ceará and Piauí in the NFZ between 2018 and 2023. Phylogenetic analysis of full-length E2 and whole genome sequences confirmed that all isolates belonged to a distinct clade of CSFV sub-genotype 1.5, indicating ongoing viral evolution. When six weaned piglets were intranasally inoculated with CSFV Brazil 2019-0571, a representative isolate, they developed mild clinical signs and lesions. Despite mild clinical signs, the piglets developed viremia and shed virus throughout the study. At the conclusion of the study, three pigs had seroconverted and developed neutralizing antibodies. These findings suggest that the circulating CSFV sub-genotype 1.5 strains in the NFZ in Brazil are of low virulence, emphasizing the need for a continuous, multi-pronged approach including clinical, serological, and virological surveillance for the effective control and eradication of CSF in Brazil.