Immunofluorescent and electron microscopic studies of feline small intestinal organ cultures infected with feline infectious peritonitis virus.

The pathogenesis, morphology, and morphogenesis of feline infectious peritonitis virus were studied in feline small intestinal organ cultures. Characteristic coronaviruses were demonstrated by electron microscopy in the extracellular organ culture fluid taken at 1 through 12, 15, 22, 31, and 43 days after the cultures were inoculated. Viral particles had a mean diameter of 94 nm. Numerous petal-shaped projections approximately 15 nm long were seen on the envelopes. Specific immunofluorescence was detected in the absorptive epithelial cells of villi of small intestinal organ cultures at 1 through 12 days after they were inoculated. By electron microscopy, coronavirus particles were observed entirely in the cytoplasm of the infected columnar epithelial cells of villi with no apparent nuclear involvement. Thin sections of the villous epithelium of small intestinal organ cultures showed a number of ultrastructural alterations, and morphogenesis of feline infectious peritonitis virus in the absorptive epithelial cells of villi was consistent with that for other known human animal coronaviruses.