Feline Coronavirus Regarding Infectious Diseases in Cats and PCR Testing: Is it truly accurate?!

Feline Coronavirus
Regarding Infectious Diseases in Cats and PCR Testing: Is it truly accurate?! By Asst. Prof. Sompoth Weerakul, DVM, PhD

When we suspect a Feline Coronavirus (FCoV) infection, we increasingly turn to PCR testing, don't we? But how much do we truly know about this virus in cats? While modern Real-time PCR offers high sensitivity and specificity, if the test is not specific to the pathogenic strains in cats, how can we be certain it is truly Feline Coronavirus when the results are interpreted?

Feline Coronavirus is a positive-stranded RNA virus. It belongs to the species Alphacoronavirus 1 within the family Coronaviridae and the genus Alphacoronavirus, which includes certain types that can cause disease in swine and dogs. In cats, the disease manifests in two forms: Feline Enteric Coronavirus (FECV) and Feline Infectious Peritonitis Virus (FIPV), the latter of which causes FIP. These exist as both low-virulence and high-virulence strains within the same species, ranging from asymptomatic carriers to severe clinical disease.

Identified strains include Feline Coronavirus C1je, Type I, Type II, and FIPV WSU79-1146. Consequently, certain types of PCR testing that are not strain-specific may fail to identify the exact cause, even if the animal exhibits symptoms. It is well-understood that identifying the specific coronavirus infecting a cat is quite complicated. Practitioners and veterinarians cannot definitively label it as a feline-pathogenic coronavirus; they can only state that a coronavirus was detected unless the specific strain or type is identified first. Furthermore, identifying the type or strain is crucial to distinguish between FECV and FIPV, or to differentiate between low and high virulence. Coronavirus serotypes differ by antigens, which impacts vaccination and immunity. One must be cautious, as the inability to identify the strain can lead to errors. Additionally, Canine Coronavirus (CCoV) belongs to the same species and differs in its S protein, which involves even further intricate details.

To gain a clearer understanding, we must look at the Coronaviridae family, which is divided into Alpha, Beta, Gamma, and Delta. The genus Alphacoronavirus was the first group identified to cause disease in humans and various animals across several sub-species. Examples include Colacovirus, Rhinacivirus, Minunacovirus, and Decacovirus in bats; Sunacovirus in shrews; Minacovirus in mink and ferrets; Luchacovirus in rats; and Duvinacovirus and Setracovirus in humans. It isn't limited to cats, dogs, and pigs; the species Alphacoronavirus 1 falls under the sub-genus Tegacovirus, which can also infect humans (e.g., Human CCoV-HuPn-2018).

Coronaviruses are highly diverse, much like SARS-CoV-2, which has been found to evolve into many variants.

Therefore, before deciding to use PCR as the definitive indicator for a species-specific coronavirus, one should inquire clearly about the diagnostic techniques used and their specificity toward particular strains and serotypes. Otherwise, it may lead to an incorrect final diagnosis.

However, in clinical practice where options may be limited, practitioners should carefully consider clinical symptoms, laboratory results, and other environmental factors in conjunction with the diagnosis.

Please read the related article: "Recommendations for Testing and Real-time PCR Results: What Veterinarians Need to Know"

Special thanks to Dr. Paweena Kongsanan (MT) for providing us with knowledge and understanding.