cat flu - information for breeders

Despite vaccination, cat flu remains a common problem in many breeding colonies. The disease is apparently mild in some households and restricted to a minor outbreak of sneezing that improves with no treatment. In other colonies, the disease is much more severe and can leave kittens with chronic disease and difficult to sell, or cause deaths of individuals or entire litters. Breeders who do have a problem with cat flu can spend a lot of time and money on investigation, and even then are still at a loss with how to control the disease. Cat flu is an important cause of illness and death in breeding colonies and its control needs to be approached in a sensible manner. Good control of flu may involve re-homing or neutering of some breeding stock.

Most breeders will agree that they know what cat flu is. It is an infectious respiratory tract disease of cats, often seen in kittens in the breeding household and seemingly not affecting the adults. The typical combination of symptoms includes discharge from the nose and eyes, ulcers in the mouth, reluctance to eat and drink, sometimes coughing, fever, difficulty breathing and, rarely, death. Which symptoms occur probably depends upon a number of factors, including not only the infectious agent present but also on management factors within the colony.

There are many causes of cat flu. Probably the most common are the two upper respiratory tract viruses, feline herpesvirus (FHV, also known as feline viral rhinotracheitis [FVR]) and feline calicivirus (FCV) which, along with a bacterium called Bordetella bronchiseptica, are most commonly detected in cats with typical signs of cat flu. Although Chlamydophila disease is often discussed at the same time as flu, in cats with Chlamydophila felis infection the signs are almost always restricted to the eyes and the serious flu signs are not seen.

Probably the most common source of infection for cats in pet homes is sick cats, especially if the new cat or kitten comes from a rescue colony or from another pet home where the cats are unvaccinated. In breeding households the disease can be caught from sick cats, but also important is the role of the apparently healthy carrier cat (see below). In order to understand this it is important to think a little about the individual infections.

There is only one 'strain' of FHV and it usually causes severe signs of flu. Thick secretions can block the nose and glue up the eyes, needing careful nursing care and antibiotic cover. Kittens are often very quiet, unable or unwilling to eat and have a high temperature. Some kittens, or adults with pre-existing diseases that suppress the immune system (eg, FIV, diabetes, cancer chemotherapy or on steroid therapy), may die.

For infected cats, it can take weeks for the signs to improve. The virus infection can cause severe damage to the delicate respiratory and eye tissues leading to long-term problems such as a chronic rhinitis (snotty nose) or conjunctivitis (runny eyes). Even in cats that recover entirely, those that have been infected by FHV are infected for life, becoming 'carriers' of the infection. Cats that are carriers of FHV do not shed virus all the time - it 'hides' in the cat and is only shed at times of stress. Known stresses that can start a cat shedding virus include re-homing, going to shows or catteries (including stud), having kittens or lactating.

In studies, carrier cats start to shed virus around one week after the stress and shed the virus for up to 14 days after that. Some cats do show mild signs of flu when they are shedding virus, but many cats have no symptoms at all. It can be hard to detect carrier cats, as they do not shed virus all the time, and a negative swab cannot therefore be taken to mean that the cat is clear. A positive swab on the other hand does mean that the cat is infected. The virus cannot be eliminated from carrier cats. As an infected queen will usually infect successive litters of kittens, probably the best way to manage cats known to be infected with FHV is to remove them from the breeding population by neutering and re-homing.

There are many strains of FCV, some of which appear to cause more severe disease than others. In general, FCV usually causes milder signs than FHV, often restricted to mild nasal discharge, conjunctivitis and the development of ulcers in the mouth. Even though these ulcers can be quite large, affected animals rarely have poor appetite and are usually still quite bright. In some cases the breeder is not aware that the kittens are ill. Though severe disease is less common than with FHV, FCV can still leave the kitten open to bacterial infection and antibiotics and nursing care are needed.

Occasionally the virus causes a dramatically different disease, so called 'pyrexia and limping syndrome', where kittens suddenly become lame on one or more legs and get a high temperature. Though dramatically ill, kittens usually get better rapidly with no treatment or with painkillers.

Another disease associated with FCV infection is gingivitis - inflammation of the gums. Gingivitis is very common in the pedigree cat population and many affected cats are found to be shedding FCV.

Cats that have been infected with FCV also become carriers. However, the carrier state for FCV is rather different to that for FHV. In FCV, recovered cats shed the virus for a variable length of time, but they do so continuously. Most cats shed the virus for at least one month after infection, but by two to three months approximately half of infected cats will have stopped shedding. As time goes on, the majority of cats do eventually eliminate FCV, though some cats shed the virus for years. As shedding is continuous, it is easier to decide if a cat is a carrier by looking for the virus. It is also possible to trace a cat to see if/when it stops shedding virus and may have eliminated the infection. However, because there are many strains of FCV, it is possible for cats to be infected several times with different strains, especially if the cat visits cat shows, seminars, studs, etc. Because the disease can be mild in adults, in particular if they have met FCV before or are vaccinated, it is not always noticed that the cat is ill. An FCV strain that causes mild disease in adults though, can cause more severe problems in relatively naive kittens. More recently more virulent strains of FCV have been identified in the USA and UK. Among other clinical signs these strains often cause severe swelling of the face and paws, skin ulcerations on the head and limbs, and jaundice (yellow gums and skin). They have deleterious effects on the whole body with a high mortality rate (up to 67%). Affected adult cats appear to suffer from more severe clinical signs compared with affected kittens. Many of the cats with this condition had been fully vaccinated. Further investigations into these strains are currently ongoing.

This bacterial infection has become recognised as a problem in cats only recently. Although well known in other species, until 10 years ago it was not really reported in the general cat population. In breeding colonies, in combination with FHV and/or FCV, it can cause fatal pneumonia, with death of entire litters within hours or days. On its own (in experimental studies) this bacterium usually causes a mild nasal discharge and perhaps a slight cough. In experimental studies there also appears to be a carrier state, and queens have been shown to shed bordetella in the post-kittening period. The role of bordetella in cat flu is still being investigated and several studies on this bacterium are in progress. It is now possible for researchers to 'type' different strains and what makes some strains cause disease is an area under active study. Using this strain typing system, it has also been shown that this bacterium has, in a small number of cases, been transmitted from dogs (in which it causes kennel cough) to cats.

Some typical questions about flu from breeders are shown below. In all cases, it is essential to involve your vet if your cats suffer from an outbreak of flu. Your vet may want to speak to one of the veterinary schools for advice with each individual disease problem.

Unfortunately the answer is probably yes. In a 1994 survey of cats at several shows in the UK, between 20 and 30% of the cats present were found to be shedding FCV and about 1% were shedding FHV. It is notable that these cats were all apparently healthy and had passed vetting in. Though disinfectants are used between cats it is certainly possible that transmission could occur at shows from coats or other equipment used by vets, judges or stewards, not to mention the risk from the public touching cats. It must also be borne in mind that going to shows constitutes a 'stress' and that many FHV carriers would be expected to shed FHV following a stress - in some cases with signs of disease. So a cat that gets flu after a show may not have picked it up there - the stress of going to the show could have caused the reappearance of the disease.

I have had flu in several litters. How can I find out which infection is present?

If you have a problem with cat flu in a breeding cattery, then your vet may have a suspicion of which infection is present on the symptoms your cat/kittens are showing, but you will probably need to do some tests to be sure. In order to look for the viruses, your vet needs to take a mouth or eye swab. Depending on the test required the swab will have to be placed in special medium supplied by the laboratory (virus isolation) or can be submitted as a dry swab (PCR). A second swab has to be taken and placed in different medium to look for Bordetella species. These tests can only be done at specialist laboratories, often the university veterinary schools working on these infections.

A diagnosis of FHV infection in a breeding cattery can be very serious. If found in kittens, they have presumably caught it from other cats in the household, suggesting the household has at least one carrier cat. Though the queen is the number one suspect it is very important to remember that with FHV cats shed only intermittently - so 'negative' cats in the household may still be carriers, they just don't happen to be shedding at that time. Infected queens tend to infect every litter of kittens born to them, often while they are quite young. Depending upon the age at which the kittens become infected they may or may not become ill. Sometimes, the immunity passed from the queen in her milk protects the kittens from clinical signs but still allows them to be infected and become carriers. At other times the infection causes severe disease in the kittens. If the queen produces successive litters of badly affected kittens, unless she is extremely valuable to the gene pool the best advice is usually to neuter and rehome her - the only other alternative is to isolate, early wean and hand rear the kittens.

FCV is very common in the breeding cat population. As many strains are present, the best course of action rather depends upon individual circumstances. If, for example, many litters of kittens get severe signs of flu, then the best course of action will usually be to stop breeding and to wait a few months before testing the cats again. This approach may allow the detection of carrier cats and their removal or continued isolation from the rest of the cattery.

In my last litter of kittens, two have died and Bordetella species was found at post mortem examination. What should I do now?

Because bordetella is a bacterium, the infection can be treated with antibiotics. It is best to test the specific strain isolated from individual catteries to judge which antibiotic it is best to use. It is not known whether the use of antibiotics will prevent cats from becoming carriers, as this research has not yet been done. In other species it can be difficult to eliminate the infection from individual animals, though the signs of disease can often be controlled.

All my cats are vaccinated correctly. Why have I got flu in my cattery ?

The available vaccines do a very good job of preventing disease due to FCV and FHV, both in the general population and in catteries. However, no vaccine is 100% effective all the time in every animal. Factors involved in this include:

Strain variation: some strains appear to be more virulent than others, causing more severe disease and may be able to 'break through' vaccine induced immunity. Particularly with FCV, the current vaccines do not protect against all strains, so disease is still possible even in vaccinated cats.
Young, susceptible kittens are born into or brought into the breeding household, where there are often a large number of cats that may be carriers. The presence of carrier cats is particularly important - these cats can infect kittens before they are usually considered old enough to be vaccinated. In special circumstances it is possible to vaccinate kittens at a younger age, but this must be discussed carefully with your vet.
Vaccinated cats, though usually protected against the disease, can still become infected and can become carriers.
There is now an intranasal vaccine available in the UK with good efficacy against bordetella.

If you are vaccinating correctly and still have a problem, you should discuss this with your vet. It is usually possible to investigate such problems, sometimes in conjunction with the drug company that produces the vaccine, which can be helpful in producing a plan for control.

Build up of infection can occur in the household, especially where cats are kept in an area that cannot be adequately disinfected. Feline herpesvirus is a relatively fragile virus and does not remain infectious for very long in the environment (about 48 hours) but FCV can remain infectious for up to 10 days in good conditions. Use of a suitable disinfectant is essential, as is sensible stock management.

One of the factors involved in flu is keeping a lot of cats together. The more cats you have, the more likely one will be a carrier and will infect the others. Therefore, it is usually best to try to keep cats in smaller groups. This is usually only possible where cats have separate accommodation in outdoor pens or an indoor cattery. Isolation of two or three cats in back bedrooms or other areas of the house is frequently not successful, as isolation is hard to maintain. Strict hygiene is important to prevent cross infection from other groups. Management of an outbreak will usually involve isolation, treatment, vaccination and a period of testing, during which no kittens should be bred, in an attempt to control the disease. It may be necessary to consider neutering and rehoming. Individual catteries vary so much it is essential to consult your vet to produce management procedures that you can work with. In some cases this is not possible, and a certain level of disease has to be expected.