New Feline Viruses Identified
Natalie Stilwell, DVM, MS, PhD
Dr. Natalie Stilwell provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting. In addition to her DVM obtained from Auburn University, she holds a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida.
Gammaherpesvirus and morbillivirus commonly infect domestic cats worldwide, but their clinical significance remains unknown.
According to the authors of a recent article in the Journal of Feline Medicine and Surgery, “the rate at which novel viruses are being discovered now exceeds our understanding of their clinical relevance.” For example, researchers have recently identified novel gammaherpesviruses (GHVs) and morbilliviruses infecting the domestic cat, but the ability of these viruses to cause disease remains poorly understood.
Feline viral rhinotracheitis is a well-documented disease in domestic cats caused by infection with alphaherpesvirus feline herpesvirus 1.
Interestingly, recent observations show that feline immunodeficiency virus (FIV)—infected cats were developing cancers similar to those observed in humans with Epstein-Barr virus and Kaposi’s sarcoma­–associated herpesvirus. Subsequent polymerase chain reaction (PCR) screening identified 3 novel GHVs in domestic cats, bobcats, and pumas. PCR testing of nearly 1500 cats from the United States, Australia, Europe, Singapore, Japan, and Brazil has since estimated a 10% to 25% prevalence of the domestic cat GHV (known as Felis catus gammaherpesvirus 1 [FcaGHV1]). However, serologic studies suggest that infection rates are even higher than PCR results indicate.
Little is known about the epidemiology of FcaGHV1. Kittens are capable of acquiring FcaGHV1 infection at 2 months of age, and most affected adult cats are infected persistently. Prevalence is highest in male cats 2 years and older and in cats already infected with FIV or Hemoplasma species.
Although most infections are subclinical, recent studies suggest that FcaGHV1 infection increases an overall risk of illness. In 1 study, circulating herpesvirus concentrations were nearly 3 times higher in FIV-infected cats compared with baseline controls. Although researchers have failed to correlate FcaGHV1 infection with neoplasia development, 1 study found that survival after lymphoma diagnosis was significantly reduced if cats were co-infected with FcaGHV1.
Morbilliviruses, including measles, canine distemper virus, rinderpest, and phocine distemper virus, can cause significant disease in many animal species. Global screening shows that feline morbillivirus (FeMV), which was first detected in domestic cats in 2012, is now widely distributed in the United States, Brazil, Japan, and Europe.
Similar to FcaGHV1, the clinical relevance of FeMV is poorly understood, as several studies have detected a high prevalence of the virus in both healthy and ill cats. Also, the virus is notoriously difficult to isolate and PCR may cause false-positive results; therefore, test results are often difficult to interpret.
The route of infection and mode of transmission for FeMV also remain unclear. Prevalence seems to be highest in multicat environments, such as stray colonies, and there is limited evidence suggesting that the virus may cause kidney and liver disease. Although many morbilliviruses can cause persistent infection, the authors stated that further investigation is needed before the same can be stated for FeMV.
No commercial diagnostic tests have been developed for FcaGHV1 and FeMV, as continued research is still needed to understand their clinical impact. According to the authors of this review article, neither virus is believed to be zoonotic.
Dr. Stilwell provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting. In addition to her DVM obtained from Auburn University, she holds a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida.