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Feline coronavirus viremia and replication in blood in healthy shelter cats

Fish FJ, Diniz PP, et al. A cross-sectional quantitative RT-PCR study of feline coronavirus viremia and replication in peripheral blood of healthy shelter cats in Southern California. J Feline Med Surg. 2017 Apr 1:1098612X17705227. doi: 10.1177/1098612X17705227.  (Winn Funded Study, W10-036)

Feline infectious peritonitis (FIP) is a deadly infectious disease of cats, involving exposure to the ubiquitous feline (enteric) coronavirus (FCoV) biotype. FCoV is found frequently in multi-cat environments, such as shelters and catteries. This biotype, FCoV, normally replicates in feline enterocytes and usually causes a mild, self-limiting intestinal disorder. In a small percentage of cats (5-12%), the virus develops into a highly pathogenic form causing lethal FIP, this viral biotype is referred to as feline infectious peritonitis virus (FIPV). The exact method for this change in biologic behavior is not known, yet research supports viral mutation in one or more genes with or without predisposing factors such as host immune deficiency, genetic susceptibility or a combination of both.

A definitive diagnosis of FIP can be difficult in many cases.  There is the use of RT-PCR as an assay capable of detecting FCoV genomic RNA in different types of samples, such as blood, feces and tissue with a high sensitivity. The assay cannot discriminate between the FCoV and FIPV biotypes. Also, it is important to note that the detection of genomic FCoV RNA in blood of healthy cats by RT-PCR does not predict the development of FIP.

The major objectives of this study were:

  1. determining the frequency of FCoV viremia and replicating FCoV in circulating white blood cells in healthy cats in multi-cat environments. The authors hypothesized that the frequency of FCoV viremia in healthy shelter cats would be low compared with active FCoV replication in feces, and also that the frequency of cats with replicating FCoV in blood would be a smaller part of the cats with either replicating FCoV in feces or those cats with total FCoV RNA detected in blood.
  2. tracking positive cats over time, with the hypothesis that replicating FCoV in peripheral blood would be associated with development of FIP.

The investigators tested buffy coats from 205 blood samples by total FCoV RNA qRT-PCR. Out of the 205 buffy coat samples tested, nine cats (4.4%) were viremic. However when subgenomic mRNA  (suggestive of active FCoV replication) was evaluated, only one of these total FCoV-positive cats had mRNA detected. The authors state this finding confirmed that FCoV might circulate in the blood stream of a small number of cats, though only a single cat showed active replication of the virus.

In addition, none of seven of nine viremic cats followed over time or the single cat with replicating FCoV with positive qRT-PCR results developed signs compatible with FIP within 6 months of sample collection.

The low prevalence of FCoV viremia and blood replication in the study and the lack of association with development of FIP suggest that either the total FCoV RNA qRT-PCR or the FCoV mRNA qRT-PCR assays alone may be insufficient to diagnose or predict accurately the development of FIP.

The authors state that larger case-control studies are needed to evaluate the prognostic accuracy of the qRT-PCR assays. (VT)

See also:
Longstaff L, Porter E, et al. Feline coronavirus quantitative reverse transcriptase polymerase chain reaction on effusion samples in cats with and without feline infectious peritonitis. J Feline Med Surg. 2017 Feb;19(2):240-245.