Feline medicine specialists in the UK have been puzzled by reports from Japan suggesting that cats infected with feline leukaemia virus (FeLV) can be identified by their wavy whiskers.
Researchers from Nihama Animal Hospital, Ehime, Japan, say these morphological changes to the sinus hairs appear to be a consistent finding in cats that are seropositive for the virus and suggest the feature may be useful in screening for patients without obvious clinical signs of FeLV-related disease.
Feline medicine specialists in the UK have been puzzled by reports from Japan suggesting that cats infected with feline leukaemia virus (FeLV) can be identified by their wavy whiskers
However, UK vets with considerable experience in dealing with FeLV-infected patients argue that if similar changes have occurred in the domestic cat population, they have not been noticed previously. They surmise that if the unusually shaped whiskers are present in other groups of Japanese cats, it is likely due to some genetic or environmental factor absent in the European population.
They also raise questions about the methodology of the Japanese study and suggest that while the changes to the cats’ whiskers are scientifically interesting and worthy of further investigation, this feature is unlikely to be of much help in preventing further spread of the virus in UK cats.
What evidence is there?
The study, conducted by Dr Masataka Morishita and colleagues, was published in the open access journal BMC Veterinary Research.
In the paper, Masataka explains that he and his colleagues had seen several cats with unusual changes to their whiskers among those owned by clients of their first-opinion practice and noticed that many appeared to have serological evidence of FeLV infection.
They examined a total of 358 cats, including 56 with wavy changes in at least two whiskers. Among this group, 50 cats (89.3 percent) were serologically positive for FeLV.
The researchers carried out detailed investigations of the six cats with wavy whiskers but no serological evidence of having been exposed to the virus. Two were found to have chronic renal failure, one had haemobartonellosis and one had signs of traumatic injury, but there were no significant clinical findings in the other two.
What did they find?
Among the 302 animals with normal whiskers, 23 (7.6 percent) were seropositive for FeLV. The authors also conducted serological tests for feline immunodeficiency virus, to which 36 of the 358 cats had been exposed, but there was no association with the abnormally shaped whiskers.
Working with colleagues from Tottori University, the authors examined tissue samples from the affected cats. Light microscopy revealed damage to the central medulla layer of the abnormal whiskers. Immunohistochemistry showed FeLV antigens were present in the skin of the upper lip, hair follicles and associated sebaceous and sweat glands. However, if the changes in hair structure seen in these cats are related to the virus, the mechanism is still unclear.
What did they conclude?
The authors speculate about the diagnostic value of their findings. They point out that the clinical signs of FeLV infection are highly variable, and the disease progresses very slowly, so it is difficult for the owners to notice any abnormalities in their pets. “Therefore,” they concluded, “the easily observable findings on the cats’ faces may be suggestive of infection, without the need to capture or restrain the cat.”
The clinical signs of FeLV infection are highly variable, and the disease progresses very slowly, so it is difficult for the owners to notice any abnormalities in their pets
FeLV infection would normally be identified by serological methods, such as IFA, ELISA or PCR.
The authors acknowledge that the overall sensitivity of these morphological changes in identifying FeLV-positive cats is rather low at 68.4 percent. But they hope that a combination of wavy whiskers and serology “could be an effective tool” for identifying FeLV-infected cats in clinical practice.
Criticisms and controversy
Feline clinicians in the UK are unsure what to make of the paper’s findings and express some scepticism about the conduct of the trial and the clinical value of the results.
Andy Sparkes, former veterinary director of International Cat Care, said: “While this study is intriguing and should certainly stimulate further investigations of FeLV-infected cats, I think it is hard to determine the true significance of the observations based on a single study. Also, there are aspects of the study that are poorly described and confusing – which I am surprised were not picked up on peer review – that create some important questions about the population studied and the results reported.”
Conor O’Halloran, an internal medicine resident at the Royal (Dick) School of Veterinary Studies (R(D)SVS), Edinburgh, agreed that there are important gaps in the information provided in the paper. “The authors say that the cats were ‘serology positive’ for FeLV but don’t say what test they used, other than a very brief mention of the viral p27 antigen in the conclusion,” he said. “We know there are different brands of tests that have different sensitivities and specificities. So it would be interesting to know what they were using as their reference and if or how many were PCR tested.”
Andy also questions the claims made in the paper about the value of wavy whiskers as an indicator of FeLV infection. “I would be concerned about the positive predictive value […] they quote this at 89 percent, but this is entirely misleading,” he stated. “The positive predictive value of a test is entirely dependent on the prevalence of disease, and if you took the prevalence of FeLV to be 2 percent in a typical cat population, the PPV would actually be around 39 to 40 percent.”
‘If you took the prevalence of FeLV to be 2 percent in a typical cat population, the PPV would actually be around 39 to 40 percent’
Neither Andy nor the Edinburgh team say they have noticed wavy whiskers like those seen in the Japanese cats in their patients. Furthermore, there have not been any previous reports in the veterinary literature of these very obvious changes.
However, Professor Danielle Gunn-Moore, head of feline medicine at the R(D)SVS, offers a possible solution to the puzzle. She observed that personal communications from colleagues in Australia indicate that similar changes have been described in that country’s feline population. It is certainly possible, she suggests, that the reported changes could be linked to a particular strain of FeLV only present in the feline population in those two countries.