Upper respiratory infections (URIs, Cat flu) – information for breeders


Upper respiratory infections (URIs, cat flu) remain a common problem in many breeding colonies.

The disease is mild in some households and may be restricted to minor outbreaks of sneezing that improve rapidly. In other situations, the disease is much more severe and can leave kittens with long-term disease, such as chronic rhinitis (long-term inflammation and infection within the nose). Occasionally, the infections can be so severe as to cause deaths of individuals or entire litters of kittens.

Breeders who do have problems with URIs can spend a lot of time and money on investigation, but even then can struggle with how to control the disease – its control needs to be approached in a sensible manner but is not always straightforward.  

What causes URIs (cat flu)? 

Most cat URIs are caused by infection with one or both of the cat flu viruses:

These two viruses are thought to be responsible for more than 90% of URIs in cats (upper respiratory infections (URIs) – cat flu). Other important organisms that may be involved in some cases include:

Most breeders will agree that they know what URIs are; infectious upper respiratory tract diseases of cats, often seen in kittens in the breeding household. Most adults that harbour the infection won't show clinical signs. Typically, kittens will develop signs when they are around 6-10 weeks of age.

It is likely that virtually every breeding household will actually have cats infected with respiratory viruses (FCV and FHV). Infection is very widespread among cats, and environments where cats are kept together in groups are ideal for the virus to persist. Many cats may remain carriers of these viruses after being first infected; with FHV virtually all infected cats will become carriers, although not all will shed the virus, and with FCV most cats will shed virus for weeks to months after initial infection, but some may shed the virus for years.

How do upper respiratory viruses get in to a cattery?

Many cats – both breeding cats and household pet cats, can be asymptomatically infected with FHV or FCV (‘carrier’ cats). Because these cats exist, and because these viruses are so widespread throughout the world it is effectively impossible to keep them out of a cattery.

Infection may be introduced if a new cat comes into the cattery, if one of the existing cats visits another cattery (e.g., for breeding purposes), through close contact with other cats at cat shows etc., and even through indirect contact. FHV can survive for up to 2 days in the environment, and FCV perhaps up to as much as 4 weeks so these viruses can also be transmitted on hands, clothing, objects etc.

Once present within a cattery, the viruses are virtually impossible to eliminate, at least on a practical basis. Adult cats may often be carriers and may shed the viruses permanently or intermittently, and thus be a source of infection to susceptible kittens. A queen herself may pass infection on to kittens – any queen previously infected with FHV will be a permanent carrier and the stress of kittening will often result in re-shedding of FHV which can then be passed to the kittens (although the queen may show no signs herself).

How many cats are infected with upper respiratory viruses?

One large pan-European study was conducted looking at over 200 breeding, rescue and private households with at least five cats in each household. This study looked at a total of more than 1700 cats and found the frequency of infection with FCV and FHV was 29% and 8% respectively in catteries without ongoing respiratory disease, and 47% and 16% respectively in catteries with ongoing respiratory disease. This study used PCR to identify the presence of organisms, which is a sensitive test, but especially with FHV (which is only shed intermittently) it will still significantly underestimate the true number of cats infected.

This study, and others, show that infection with these viruses is extremely widespread among cat populations.

Determining the cause of problems

If you have repeated problems with URIs, especially among kittens, it is sensible to work out what particular agents are involved. Mouth, throat and eye swabs can be taken to look for the four major organisms involved – FCV, FHVBordetella bronchiseptica and Chlamydophila felis. These swabs need to be sent to a veterinary diagnostic laboratory where the organisms can be isolated by culture or detected using PCR (polymerase chain reaction – a molecular technique to identify the genetic material of the organism).

Determining what organisms are involved is important, as some are directly treatable (e.g., Bordetella bronchiseptica and Chlamydophila felis will respond to appropriate antibiotics), and some antiviral preparations are effective in managing FHV infections.

Control of FHV and FCV in a breeding cattery

Control of upper respiratory viruses in a breeding cattery can be problematic. Measures to control infection are particularly important where there are repeated infections occurring in groups of kittens. Where this is happening a number of measures are important to consider:

  • Keep cats in small isolated groups – ideally with no more than 4-5 cats in each group – this is helpful in controlling any infectious disease within the cattery
  • Make sure that excellent hygiene measures are in place with good cleaning and disinfection, washing of food and water bowls, cleaning of all utensils, washing and disinfection of litter trays etc.
  • Keep the cats as stress-free as possible
  • Make sure all cats are regularly vaccinated
  • Give a booster vaccination to queens just before they are mated – this ensures they will provide maximum immunity to their kittens. The kittens will get antibodies from the queen when they suck milk in the first 12-24 hours after being born, and these ‘maternally-derived antibodies’ (MDA) are critical in protecting them against disease in the first weeks of life
  • Avoid breeding from queens that repeatedly produce litters of kittens affected with respiratory disease – the queen herself may be passing on infection to the kittens
  • Move queens into isolation 2-3 weeks before they are due to kitten so that the newborn kittens are not exposed to other cats in the cattery that may be carriers of viruses
  • Keep the queen and kittens isolated until the kittens are vaccinated
  • If necessary, consider early-weaning the kittens (at 4-5 weeks of age) when they should still be protected by MDA and keep the kittens isolated from all other cats until vaccinated
  • Consider early vaccination of the kittens, for example, starting at 6 weeks of age and repeat vaccination every 3 weeks until 12-16 weeks of age

Always discuss the problem with your vet, and seek their help and advice, but some or all of the above measures may be helpful in controlling respiratory virus infections.

What to do when Bordetella infection is present

Although much less common than FCV or FHV infections, the bacterium Bordetella bronchiseptica can be involved in some cases of upper respiratory infections in catteries, and can sometimes cause a fatal pneumonia in kittens. See Bordetella bronchiseptica in cats.

If your vet suspects Bordetella bronchiseptica may be involved, the organism can be looked for in throat swabs taken from affected cats.

Because Bordetella bronchiseptica is a bacterium, the infection can be treated with appropriate antibiotics (e.g., doxycycline) although it is best to get the laboratory to undertake sensitivity testing of the specific strain isolated to determine which antibiotic is best to use. Where Bordetella bronchiseptica is causing a significant problem within a cattery, a good and effective vaccine (administered intra-nasally) is available in many countries and this can help to control the problem.

Why can URIs be a problem despite good vaccination?

The available vaccines do a very good job of preventing disease due to FCV and FHV, both in the pet cat population and in catteries. However, no vaccine is 100% effective and there are some particular difficulties with FCV and FHV:

  • Strain variation – with FCV the virus constantly mutates and so multiple different strains exist. It is not possible for vaccines to protect against all strains of the virus, although some newer vaccines use more than one strain and provide broader protection
  • Amount of virus a cat is exposed to – even with the best vaccines, if a cat or kitten is exposed to high levels of the virus, this may overwhelm vaccine-induced immunity and still cause disease
  • Type of immune response – with both FCV and FHV infections, immunity relies on what is termed ‘cell mediated immunity’ as well as the production of antibodies by the immune system. It is often more difficult to simulate high levels of cell mediated immunity than it is with antibody production
  • Waning maternal immunity and exposure to the virus – in breeding catteries, problems often exist because there can be a gap between the time at which maternal-derived immunity wanes (the antibodies passed on to the kittens from the queen) and the time at which vaccine-induced immunity starts. This means kittens are often most vulnerable to infection between around 6 and 10 weeks of age. Early vaccination may help to overcome this and can be discussed with your vet

For these (and other) reasons, protection by vaccination is not always completely straightforward. However, despite some limitations, vaccination is extremely important and provides much-needed protection. Vaccinated cats are usually protected against developing clinical disease (or at least severe disease), but it is important to remember that at least some vaccinated cats can still become infected with FCV and FHV, and can still become carriers of the viruses.