Enteritis due to feline infectious peritonitis virus [Japan]

Four clinically, pathologically and serologically diagnosed cases of fatal feline infectious peritonitis (FIP) as well as 14 experimentally infected cases were examined for gut lesions and local presence of viral antigen and particles by immunofluorescence or electronmicroscopy, respectively. Two of 4 naturally occurring cases and 12 of 14 orally infected cases had diarrhea. In most of these cases the small and large intestines showed edematous thickening of either anemic or hyperemic mucosa with watery or mucous content. Histopathologically the enteric lesions in 3 natural and 12 experimental cases were rather superficial and characterized by degeneration, desquamation and hyperplasia of epithelial cells and edematous tunica propria with some infiltration of neutrophils and mononuclear cells. Fusion of epithelial cells was frequently encountered. In the remaining 1 natural and 2 experimental fatal cases, however, the deep mucosa of the small and large intestines was also severely affected with remarkable cell infiltration. By immunofluorescence virus-specific antigen was detected in the cytoplasm of intestinal epithelial cells of natural as well as experimental cases. Electronmicroscopy revealed coronavirus particles within the same cells as well as in feces. The findings suggest that fecal excretion of the virus from intestinal lesion may be of importance for transmission of FIP.