Feline Leukaemia Virus (FeLV): What Every Owner Should Know

In this guide

Feline leukaemia virus, or FeLV, is a retrovirus that causes more feline deaths than any other single organism, and it is unfortunately not rare. It spreads easily between cats that have had close contact, through saliva, urine, shared litter trays, nursing, or bites. Kittens can also be born with the virus if their mother was infected, and kittens along with cats with compromised immune systems are more vulnerable overall.

Four types of infection

• Abortive infection — the cat mounts an early, effective immune response, viral replication never really gets going, and infected cells are cleared. These cats test negative for the virus in the blood.
• Regressive infection — replication is limited, leaving only a small population of infected cells. These cats test negative on standard testing but positive on a more sensitive PCR test; many go on to clear the virus entirely, and while not contagious through normal contact, they may still transmit the virus via blood transfusion.
• Latent infection — a moderate number of cells remain infected, again testing negative on the standard test but positive on PCR. The virus retains the potential to reactivate later, though these cats are not contagious while the infection stays latent.
• Progressive infection — full viral replication occurs, and both virus and genetic material are detectable in the blood. These cats actively shed the virus, mainly in saliva and faeces, and are the ones most likely to become seriously ill from FeLV-related disease.

Signs and diagnosis

Symptoms can take anywhere from a few weeks to several years to appear after infection. Once the virus becomes active, cats can show weight loss, diarrhoea, loss of appetite, swollen lymph nodes, fever, infections of the bladder, skin or respiratory system, weakness, and infertility.

A simple blood test, available at most veterinary practices with results in about 30 minutes, confirms whether a cat is FeLV positive. Your vet may also recommend blood chemistry, haematology, x-rays, a bone marrow sample, or specific antibody testing to build a fuller picture.

Treatment and prevention

There is currently no treatment that reverses FeLV once a cat is infected. Any new cat or kitten joining a household should be tested first, then vaccinated if the test comes back negative. Preventing contact with FeLV-positive cats is the main defence, particularly relevant for cats with outdoor access. All outdoor cats should stay current on their FeLV vaccination, and it may also be worth considering for indoor cats; your vet can advise on the right vaccination schedule for your particular pet.

Caring for a FeLV-positive cat

The outlook varies considerably depending on the type of infection and the level of supportive care available. Cats with persistent infection typically live between two and a half and three years, though others remain healthy for much longer. Because FeLV suppresses the immune system, these cats are more prone to secondary illnesses, making annual vet visits, at minimum, genuinely important. FeLV-positive cats should be kept strictly indoors and, ideally, in a single-cat household unless housed alongside other FeLV-positive cats.

One reassuring fact: the virus is fragile outside the body, surviving only minutes and easily destroyed by most household disinfectants. This means a new, healthy cat can safely move into a home shortly after an FeLV-positive cat has left, provided normal hygiene and cleaning have been carried out. Speak to your vet if you have further questions about the virus.

Article content © Ravi Teja. All rights reserved.