Genetic characterization of two feline enteric coronaviruses in China and their pathogenicity in domestic cats.

Feline coronavirus (FCoV) exists in two primary pathotypes, feline infectious peritonitis virus (FIPV) and feline enteric coronavirus (FECV), which are prevalent in cat populations worldwide. FECV is highly prevalent in cat populations but is associated with low mortality. FIPV causes feline infectious peritonitis (FIP), a fatal systemic disease in cats. The prevailing hypothesis posits that FIPV arises from mutations in FECV. FECV is highly prevalent among cats in China, but studies on genetic characteristics of circulating strains and their pathogenicity in domestic cats remain limited. In the present study, two complete genome sequences were independently obtained from FECV type I RNA-positive fecal samples using next-generation sequencing (NGS) and were designated GD/2023/Fecal01 and GD/2023/Fecal02 respectively. The genome sequences were then systematically analyzed. In addition, pathogenicity of GD/2023/Fecal01 and GD/2023/Fecal02 was assessed in cats. Cats aged 1-2 months were divided into three groups and orally inoculated with processed fecal filtrate containing GD/2023/Fecal01, processed fecal filtrate containing GD/2023/Fecal02, or DMEM (control), respectively. Pathogenicity was assessed by monitoring clinical signs, quantifying viral RNA in rectal swabs and tissues, measuring antibody responses, and evaluating histopathological lesions with immunohistochemistry. Following inoculation, infected cats exhibited reduced weight gain and mild transient temperature elevations. Histopathological examination identified the intestines as the primary target. The highest viral loads were detected in the rectum, followed by the colon and cecum. These results demonstrate that FECV exhibits tropism for the distal intestine and can lead to prolonged shedding. This study provides new insights into FECV pathogenesis.