Feline leukaemia virus (FeLV) is high on the list of causes of mortality in the young adult cat. FeLV is a retrovirus which once it infects a cat can make a DNA copy of itself inside the cells, especially rapidly dividing cells, e.g., bone marrow, salivary glands and respiratory tract.
The source of infection is from another cat infected with the FeLV virus. The virus is found in the saliva and licking seems to be the main mode of transmission.
Once exposed to FeLv most cats will throw the infection off completely. In a smaller number of cases (perhaps about 25%) there may be extensive multiplication of the virus in the bone marrow and other organs of the body including the salivary glands. The incubation period varies from four to thirty weeks.
Two main factors that determine whether a cat exposed to FeLv will become permanently infected or not are: age of infection and the amount of virus to which they are exposed. Kittens under eight weeks where the immune system is not yet mature and born from FeLv positive mothers, are at very high risk and are almost always infected for life. The disease is more likely to spread in households of cats with much social contact as opposed to colonies of stray or feral cats where interaction may be rarer.
In the 25% of infected cats that go on to be persistently infected, the virus can go on to cause the following diseases:-
Other than symptomatic treatment of the related diseases accompanying FeLv, there is at the present time of writing (2017) no cure for this disease.
Antibodies to the disease can be detected by and ELISA test which can be performed rapidly ‘in house’ by your vet or in some cases samples sent away for virus isolation. Your vet will discuss the testing protocol for your own particular situation and may well recommend that cats which are showing no clinical symptoms of FeLv (but positive on an ELISA test), be re-tested at twelve week intervals.
There are several vaccines currently on the market that will provide excellent protection for your cat, but do remember that no vaccine is completely 100% effective.