Detection of feline coronavirus type II infections in blood of cats using a reverse transcriptase polymerase-chain reaction (RT-PCR)

In order to detect coronaviral RNA in blood samples of cats infected with feline coronaviruses type II a reverse transcriptase PCR (RT-PCR) was developed. 81 blood samples were tested in parallel for the presence of viral RNA by the RT-PCR and for antibodies using an immunofluorescence assay. 39 % of the clinically healthy cats without a special risk of coronavirus infection were seropositive and 57 % PCR-positive; in the group of clinically healthy cats, but with a higher risk for infection, 85 % showed antibodies and 95 % were identified as virus carriers; 100 % of the cats with symptoms of Feline Infectious Peritonitis (FIP) were seropositive and 90 % PCR-positive; in the group of cats with unspecific clinical symptoms 61 % were seropositive and 82 % PCR-positive. In 57 % of the seronegative animals viral RNA could be detected. As most of these cats were between 8 and 12 weeks of age, it is probable that the blood samples were collected during the time of seroconversion after the first infection with feline coronaviruses. These results show that the RT-PCR proves helpful in identifying latent virus carriers, not only among seropositive animals, but especially among seronegative cats during the period of seroconversion. So it will be a tool to prevent spreading of feline coronavirus infections into free catteries. However, the RT-PCR is not suitable for diagnosing FIP, as a high percentage of virus carriers was detected among ill as well as healthy cats.