Feline Leukemia Virus

Feline Leukemia Virus (FeLV)

Feline leukemia virus is a member of the retrovirus family and is one of the few viruses that has been specifically linked to the formation of cancer (oncogenic). Infected cats can spread the virus through any secretions from the body however saliva is considered the most common source of infection generally through cats grooming each other. It should be noted that the virus doesn't last long outside the body and prolonged contact (weeks to months) is usually required for virus spread so casual contact is unlikely to lead to infection. For this reason FeLV has often been a problem in catteries or households with multiple cats. Younger cats are also more susceptable to infection and it is even possible for an infected queen (mother cat) to passe the virus to her kittens whilst they are in the uterus (womb).

When cats become infected through the mouth the virus enters the local lymph nodes (glands) in the pharynx (throat) and start of the intestines (gut). Over the next one or two weeks the virus multiplies in these lymph nodes. During this time the cat will either successfully overcome and eliminate the virus, or it spreaads to the bone marrow and further multiplies. Once established in the marrow the FeLV virus is able to spread via the blood stream (viremia) to other parts of the body and may be excreted in body fluids. One further outcome is also possible called latency. In these cats the virus remains localised in specific tissues particularly the bone marrow without developing to a viremia.

Clinical signs related to FeLV can be divided into two processes neoplasia (cancer related) and immunosuppression (lowering the bodies defences)

Neoplasia results from the viruses ability to transfrom (change) cells in the hemopoetic system (where red and white blood cells are formed). Lymphosarcoma (cancer of the lymphocytes) is the specific tumor associated with FeLV. It is suspected that most lymphosarcomas in cats are secondary to FeLV infection. A number of different types of lymphosarcoma are recognised (see Lymphosarcoma topic for details).

Immunosuppression leads to reduced ablilty to fight infection. Commonly this shows as loss of appetite and weight sores around the mouth and gums, rhinitis (persistently runny nose) and conjunctivitis (mucky eyes). FeLV may also have a role in other specific infections such as Feline Infectious Peritonitis, and Hemobartonella felis.
It can cause anemia (reduced red blood cells) either by directly damaging the cells or reducing their production in the bone marrow.

There is no specific treatment for FeLV.The focus with this disease is control through identification of infected individuals and vaccination of uninfected cats.
Test for FeLV are directed at identifying the virus. Antibody tests are of limited value as they tend to mainly identify recovered animals.
Viral tests of blood available are Indirect Immonofluorescence, ELISA, and CITE test.
Some of these tests are now available as simple kits which allow testing to be performed in the veterinary surgery during a consultation. There is however inaccuracy associated with all of these tests especially with positive resluts so multiple testing including virus isolation from marrow may be required.

A number of vaccines are now available against FeLV. It is generally recommended that cats are tested for the virus before being vaccinated.