Single-site mutation (M1058L) of feline infectious peritonitis virus (FIPV) spike protein in domestic cats of Northern Vietnam.

Feline coronavirus (FCoV) has two biotypes: feline enteric coronavirus (FECV), which typically causes mild intestinal infections, and feline infectious peritonitis virus (FIPV), a virulent form associated with a fatal systemic and infectious disease in cats, known as feline infectious peritonitis (FIP). The differentiation between FECV and FIPV has been linked to specific mutations, most notably M1058L and S1060A, in the spike (S) protein. These mutations are believed to enhance macrophage tropism and facilitate systemic dissemination. However, the precise contribution of these mutations to FIPV virulence remains uncertain, as they have also been reported in non-FIP cases. Here, we report three FIP-positive cases (3/20; 15%) in domestic cats in Hanoi, Vietnam, in which the virus carried the M1058L mutation, while none had the S1060A substitution. These findings contribute to the ongoing debate regarding the role of spike protein mutations in FIP pathogenesis and underscore the need for continued genomic surveillance. Further research is needed to elucidate the molecular determinants involved in the FECV-to-FIPV transition, with potential implications for improving diagnosis, treatment, and prevention strategies for feline infectious peritonitis.