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Understanding Feline Leukaemia

Understanding Feline Leukaemia

What is Feline Leukaemia (FeLV)?

Firstly, FeLV (Feline Leukaemia) should NOT be confused with FIV (Feline Immunodeficiency Virus) - they are two very different viruses. They are often mentioned together due to the 'snap' tests carried out by vets, but they differ greatly in how they affect a cat, and it's expected lifespan. FeLV is a serious risk to a cat's health and longevity, whereas FIV is not.

Like FIV, the feline leukaemia virus (FeLV) belongs to a group of viruses called 'retroviruses', but to different families within the group. Both are long-term viruses which compromise a cat's immune system, leaving him more susceptible to other infections. In addition, FeLV also causes tumours in 20-30% of infected cats.

How does a cat catch Feline Leukaemia?

Cats become infected with FeLV in two different ways:

(1) The unborn kittens are infected while in the uterus if the mother is carrying the virus. They may also be infected from her milk. This is different from FIV, where kittens are not infected by the mother, although they may receive antibodies.

(2) Cat-to-cat infection occurs only where there is prolonged, intimate contact between cats. The virus is shed in the saliva of infected cats and dies very rapidly once outside the body, so it is only likely to be transmitted as a result of close contact with an infected cat. This means mutual grooming, sharing of feeding bowls or actual biting are necessary for the infection to be passed on. Note the difference from transmission of FIV, where an actual bite is necessary for the infection to be passed to another cat - sharing of feeding bowls and mutual grooming is not considered to be a channel of infection for FIV.

FeLV is also found in tears, nasal secretions and urine from infected cats, but this is much less likely to be a source of infection to another cat than saliva. Blood is another source of infection and blood donors should always be screened for both FeLV and FIV.

What happens when a cat is exposed to infection?

This depends on the age of the cat. Resistance to infection increases with age.

Most new-born kittens will receive maternal antibodies to FeLV, which protect them if they are exposed to the virus. However, if they have not, (because their mother has not encountered it) and they are exposed to it, they will be permanently infected. In kittens between six weeks and four months (whose maternal immunity has waned), 85% exposed to the virus will be permanently infected.

Of kittens over four months or adult cats, only 15% become permanently infected. The other 85% will produce antibodies to the virus and recover from the infection. These cats will have a life-long immunity to FeLV, which can be assessed by the Virus Neutralising Antibody (or VN) test. (This test is only carried out at the Feline Virus Unit at the University of Glasgow, and the vet will send a blood sample to them.). However, many vets do not appear to have heard of this test, so you may need to ask for it specifically.

It will be obvious from this, that the most susceptible age-group to infection with FeLV is the six weeks to four month-old kitten. Of those which become permanently infected, 80-85% will die within 2-5 years. Kittens infected before birth will also die within this time-scale. The long-term outlook is not good for kittens infected at this age.

What are the signs of Feline Leukaemia?

Two to four weeks after infection the cat may be off-colour and run a temperature for a short while. This may be so slight as to be unnoticeable. After he recovers from this there are no further signs for a variable period of time - ranging from a few weeks to five years. When (and if ) signs do eventually develop, one third of the affected cats will develop tumours - either in the chest (thymus gland), bowel, lymph nodes, kidney, liver, spleen or bone marrow (true leukaemia). The remaining two-thirds develop a variety of other problems - anaemia, infertility, abortion and various infections due to the destruction of the cats natural immunity by the virus. These include Feline Infectious Peritonitis (FIP),Toxoplasmosis, Feline Infectious Anaemia and various chronic infections, such as gingivitis, skin infections and flu. Since all these conditions can cause a variety of symptoms and all the symptoms could be caused by other diseases, feline leukaemia can only be diagnosed by a blood test.

Re-published with permission from
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