Serodiagnosis for feline infectious peritonitis by immunofluorescence using infected suckling mouse brain sections

After intracerebral inoculation feline infectious peritonitis (FIP) virus was propagated in suckling mouse brain with apparent clinical signs, and serial passage was successful. A total of 83 serum and ascites samples collected from cases which were diagnosed as FIP either clinically or pathologically, were examined for antibodies to FIP virus by indirect immunofluorescence (IF) using infected suckling mouse brain sections. Seventy-seven of 83 (93%) samples were shown to have titers of 1:400 to 1:25, 600, while only 3 of 103 (3%) non-diseased cases and 4 of 71 (6%) cases with diseases other than FIP were positive at 1:400 or 1:1, 600. Some IF positive samples were examined for neutralizing ability against intracerebral virus pathogenicity for suckling mice, revealing that the IF antibody titers were almost in parallel to those of neutralizing antibody.