Feline Leukemia Virus (FeLV) is a serious viral infection of cats that is transmitted primarily through prolonged contact with the cat’s saliva or nasal secretions, so grooming or sharing water or food sources with an infected cat usually results in infection. The virus doesn’t survive in the environment so faeces, urine and aerosol transmission are less likely. Less common but possible modes of transmission are during pregnancy from mother to kittens through the placenta, after birth through the milk and during mating.

It is most common in outdoor males 1 to 6 years old.

The virus replicates in the oral/throat region and then spreads to the bone marrow where it infects white bloods cells and platelets and these then travel to the salivary and tear glands.

Whether infection occurs after exposure to the virus depends on the virus subtype/strain, the dose of the virus, the age of the cat and the cat’s immune response. Some cats can clear the virus, others will succumb to it and be persistently infected and sick or they can become latently infected where they virus lies dormant but can be reactivated during periods of stress or after treatment with immunosuppressive drugs.

Various syndromes are induced by FeLV including; lymphoma (a type of cancer of a blood cell), anaemia, immunodeficiency.

Often cats are presented with non specific signs such as anorexia, weight loss, depression or abnormalities relating to specific organ systems e.g. kidneys

The clinical signs can be due to direct effects of the virus itself or secondary opportunistic infection that can take hold because of the immunodeficency caused by the virus. Signs include gum infection and inflammation, vomiting, diarrhoea, jaundice, pneumonia, difficulty breathing or swallowing, urinary incontinence, excessive thirst/urination, cloudy eyes, constricted pupils, squinting, behavioural changes, lameness and varying degrees of paralysis.

Infected queens can abort, have stillbirths or be infertile. Kittens that are infected in the womb during pregnancy generally develop accelarated FeLV syndromes or die as part of kitten mortality complex.

Blood tests can be done to look for changes in blood cells numbers typical of the disease and x rays may reveal lymphoma masses/growths (can affect chest, intestine, kidney, liver etc)

Specific ELISA test for antibodies to the virus available at Pet Vet, this can be done using blood, tears or saliva but blood is most accurate.

There is no real treatment for FeLV, anti viral drugs have been tried but without much success, chemotherapy can be used to help with subsquent cancers (ie lymphoma and leukemia) and antibiotics are used to control/treat secondary infections. Various drugs such as anabolic steroids, vitamin B12, EPO and folic acid have been tried to help with the anaemia but again without much success, some cats will even need a blood transfusion but this will only help temporarily.

Generally the prognosis for cats that succumb to persistent infection is poor, with most only surviving 2 to 3 years.

The best method of prevention is housing indoors to prevent exposure to the virus but if cats do go outdoors as most Irish cats do the next best thing we can do to protect them is to vaccinate against FeLV.

If a cat has FeLV then it should be kept indoors to prevent spreading the virus to other cats and protect the cat itself from secondary opportunistic infection, they should also not share litter trays or water/food bowls with other cats. Keep up with regular flea control and do not feed undercooked meats or allow to hunt as these are all potential sources of opportunistic infection e.g. Toxoplasmosis, Giardia, Cryptosporidium.

Cats with latent infection (initially ELISA positive but revert to ELISA negative) are not likely to be contagious to other cats but they can pass the virus onto kittens in the womb or in milk or during labour. Also if they become immunodeficient the virus can enter their blood stream again, for example if they are given steroid drugs or go through a period of extreme stress (virus reactivation).