Feline infectious peritonitis: Role of the feline coronavirus 3c gene in intestinal tropism and pathogenicity based upon isolates from resident and adopted shelter cats

► Truncated 3c is not essential for enteric to FIP biotype conversion of feline coronaviruses (FCoVs). ► Intact 3c required by both FIP and enteric FCoV biotypes for intestinal replication in cats. ► FIP and enteric FCoV biotypes rarely infect intestinal epithelium following intraperitoneal infection. ► FIP and enteric FCoVs undergo constant mutation within and between host cats. ► Shelter cats are infected with many enteric FCoV strains reflective of their differing origins.