More about FIV - Transmission

Transmission of FIV


FIV is difficult to transmit, the main route is via a bite where the virus is actually injected into the bloodstream with the teeth of an infected cat.


There is often confusion between FIV and FeLV, this is particularly the case regarding the transmission of the virus.

The FIV virus is present in the blood and saliva, and for transmission to another cat to take place, the live virus has to enter the bloodstream of the recipient cat.

It is sometimes suggested that the virus can be transmitted via sharing food bowls and litter trays, or mutual grooming. Although this is a theoretical possibility, in reality it just doesn't happen.

There are two main reasons why FIV isn't transmitted via shared bowls or mutual grooming as is sometimes wrongly suggested:

Firstly the virus is very fragile, and does not live for long once outside the body - it is destroyed by drying, light, heat and basic detergents - normally the virus will be long-dead before any surfaces come to be cleaned, it is the initial drying that sees off the vast majority of the virus, and this will normally happen in seconds.

This is why the primary route of transmission is via a bite, where the still wet saliva containing the live virus is effectively injected through the skin directly into contact with the blood of the recipient cat.

The second reason is that the mucous membrane is a fairly effective barrier to the virus, so even if some virus does enter the cat's mouth, it is very unlikely to cross the mucous membrane, so will likely die within the stomach. It has been suggested that, for the virus to actually infect a cat when taken in through the mouth, there would need to be ten thousand times as much virus present for it to achieve a cross infection.

Interestingly, this is confirmed by the fact that kittens born to an FIV+ mother are rarely infected with the virus - although the kittens are not infected directly in the womb, as the placenta will protect them, the virus is present in the mother's milk, so all kittens will have prolonged exposure to the live virus in their digestive systems, yet it is very uncommon for the kitten to actually become infected - this is testament to how effective the mucous membrane must be in preventing transmission.

It is for these reasons that the often prescribed "keep separate from other cats" is NOT valid. FIV cats can live communally with non-FIV cats with very little risk of the virus being transmitted between them - unless the cat is a fighter and gives another cat a serious bite, which is rare with properly introduced household cats. The vast majority of cats, once neutered, will not bite other cats they live with - they may play and scrap, but this rarely leads to the serious bite required to inject the virus. There are numerous examples of households with large numbers of cats living together with FIV+ cats without the virus being transmitted (see a few here). A slow and careful introduction is required when bringing any new cat into an existing household, especially so with an FIV cat.

Where does the idea of casual transmission come from?

If you read any of the documentation put out by official bodies regarding FIV cats, they will warn of 'casual' transmission (ie transmission without biting), but, on inspection, they all refer to one single scientific study for their evidence on this matter.

It was a study carried out between 1988 and 1998 where, in a high density (of cats) enclosed rescue household, the virus was transmitted to six uninfected cats during the first six years of the study. Although the owner of the cats said there was no fighting observed, it would obviously be impossible to watch all the cats 24 hours a day for so many years. There was, therefore, a strong possibility that, in a high density enclosed household, the occasional spat could well have happened that lead to a bite (unseen and undetected by the owner).

The study did not say how transmission occurred, just that it did occur, and no fighting was observed. So it is very weak evidence for 'casual' transmission; yet is seems to be the only 'evidence' available.

It seems to be this study alone that is quoted as reference time and time again in support of casual transmission. There seems to be no other evidence of casual transmission since that last possible case in 1994 - more than 20 years ago.

Over the last couple of decades, more and more FIV cats have been living in homes together with uninfected cats, so one would have imagined that if casual transmission was a reality, there would have been more and more reported cases.

Apart from one or two individual cases of 'unexplained transmissions', there have been no reports of casual transmission at all in the last twenty years or more (as far as we are aware, and we keep looking).

See also the results from the 1000 FIV cats project where there have been no reports of transmission despite large numbers of mixed households (positive and negatives living together).


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