CAT FLU REVISITED, FHV & FCV

Trevor Turner, B. Vet. Med., MRCVS

WHAT IS CAT FLU?

Cat flu is descriptively called viral induced upper respiratory tract disease. Most cases are due to Feline Herpes Virus (FHV), or Feline Calicivirus (FCV). To make matters difficult, Feline Herpes Virus (FHV) is also still commonly known as Feline Virus Rhinotracheitis (FVR). This is by far the more serious infection. It can be responsible for very severe, sometimes fatal, cat flu and a significant proportion of recovered cats are left with chronic rhinitis (chronic snuffles). In kittens, in particular, severe conjunctivitis and eye damage can occur.

Lesser known signs include abortion and/or resorption of kittens in pregnant cats. It can also be responsible for fading kittens from infected queens. This usually occurs when the kittens are around 2-4 weeks of age.

FHV virus has a worldwide distribution and is extremely common, chiefly due to the fact that once infected, irrespective of whether the cat shows any symptoms or not, it becomes a carrier. The virus becomes latent in the trigeminal ganglia of the facial nerve. These latent carriers shed the virus often without showing any symptoms of flu following any period of stress such as being boarded, going to the vet’s or being treated with corticicosteroids. Shedding starts about a week after the stress and lasts for one to two weeks. The difficulty lies in establishing whether the cat is a carrier or not. Some carriers do not shed the virus continuously. Therefore detection depends on whether one is lucky enough to swab the cat at the time when it is actually shedding.

Vaccination, however, is fairly straightforward in that there is only one virus strain (at the moment) whereas with FCV there are many different types and vaccination will not necessarily protect against all of them.

Carrier cats can be vaccinated with no ill effects but vaccination will not stop them excreting the virus irrespective of whether it is FHV or FCV.

FELINE CALICIVIRUS

Feline calicivirus has similar worldwide distribution and ubiquitous presence. It has been shown that FCV was present in 20% of cats attending veterinary surgeries for reasons other than cat flu and over 25% of cats attending cat shows in the UK.

These figures obviously are much more likely to be accurate than any similar survey carried out with FHV since FCV carriers shed all the time whereas with FHV it is a matter of luck if the carrier cat is actually shedding when swabbed and thus can be missed.

FCV is the ulcer virus. Like FHV it can cause shifting lameness but this is rarer than with the more serious FHV.

Both viruses are relatively fragile and disinfection using household bleach at 1:32 and allowing the kennel to dry naturally before reintroduction of the cat is cheap and effective disinfection. Today of course there are more sophisticated virucides such as Trigene.

FCV virus lasts outside the body for probably up to a week compared with FHV which lasts only about 24 hours. With both viruses this depends upon the temperature and humidity.

FCV can be thought of as causing a milder form of cat flu than feline herpes virus. There are usually ulcers on the tongue and in the mouth. The cat sneezes, there is usually a nasal discharge and a clear ocular discharge. Frequently cats are left with very severe stomatitis and gingivitis. Very occasionally young kittens can suffer a so-called pneumatrophic form of FCV which causes severe pneumonia that can be rapidly fatal. This can occur in breeders’ kennels with an endemic FCV problem. It can be difficult to eliminate once it is within a breeding colony.

With both viruses it is dangerous to think that the cats will self-cure from the carrier state. Because of the difficulty with intermittent shedding with FHV we are never really quite sure whether they are still shedders or not but it has been shown with FCV that some cats do appear to cease to shed months or even years after infection. Many cats however do persist to shed for the rest of their life.

With both viruses it should be remembered that if the cat is, for any reason, immunosuppressed ( as occurs with FIV and FeLV positive cats ), that cat is much more likely to become a persistent carrier of flu viruses. Immunosuppression can be due to many causes, for example it can occur as a result of long-term administration of corticosteroids for flea allergy dermatitis.

WHAT CAN CATTERY OWNERS DO TO MINIMISE THE RISK OF FLU?

HOW CAN BREEDERS ENSURE FLU-FREE STOCK?

Cat breeders often have difficulty eliminating cat flu from their stock because of the latent carrier situation. The best strategy is to wean kittens early, by three weeks if possible, when the antibodies they will have received in the colostrum from their mother will still be circulating although declining. The kittens should then be isolated and vaccinated. Preferably intranasal vaccines should be used initially and repeated every three weeks until the kittens are 12 weeks old if there is a chronic flu problem in the cattery. Then they can receive the conventional systemic flu injections.

Also it is worthwhile bearing in mind that the cat that suddenly starts sneezing while in the cattery is much more likely to be a shedder that has become so stressed by the change of environment to suddenly develop overt signs of flu rather than, as virtually every caring owner will insist, the disease has been caught at the cattery. Even then it should be remembered from the above that because of the different strains of FCV no guarantee can be given that the cat will be protected against every form of calicivirus.

HOW OFTEN SHOULD ONE BOOST?

Regular readers will be aware that I have, of late, changed my tune regarding regular boosting. Certainly with my own animals I am no longer boosting for everything every year . When it comes to cat flu, if you run a breeding cattery and have flu problems, once you have established carrier free stock as outlined, it is certainly worthwhile for two or three years at least to boost about every six months particularly if you are going to start accepting queens or are a regular exhibitor.

It is also worthwhile having swabs examined for virus isolation, at least then you will know with certainty whether you have any FCV shedders, although it will still be a matter of luck with the FHV.

Please let me have your comments.