Feline Infectious Peritonitis: Experimental Studies

SUMMARY Virus-like particles were identified in lesions of cats with feline infectious peritonitis ( fip ) experimentally produced by bacteria-free and mycoplasma-free inoculums or nitrates. We were unable to detect by electron microscopy virus-like particles in 9 cats with naturally occurring fip . Feline leukemia virus (FeLV) antigen was detected in 9 of 20 cats with naturally occurring fip and in 2 of 15 cats with experimental fip . Evidence of vertical transmission of the FeLV as a covert viral genome in cats was found. Detection of FeLV antigen in cats with fip probably represented activation of latent FeLV by the fip agent. Feline infectious peritonitis was transmitted to 38 of 51 cats ranging in age from 5 days to 3 years. Fresh or frozen abdominal exudate, organ extracts, whole blood, and urine from cats with naturally occurring fip were capable of producing the disease by one of the following routes: intraperitoneal, intravenous, subcutaneous, or oral. We were unable to transmit the disease with tissue culture supernatant fluids from fibroblast cultures of omentum and spleen from a spontaneous case. Electrophoresis, performed on serum from 9 cats with advanced naturally occurring fip , demonstrated a diffuse hypergammaglobulinemia.