Feline Leukemie Virus (FeLV)

Overview: The feline leukemia virus is a retrovirus in the family Oncovirinae (tumour causing). It is in the same family as the FeLV virus. More deaths occur from the feline leukemia virus than any other pathogenic disease in cats.

Four subgroups of FeLV exist: A; B; C, and T, but only subgroup A is transmissible between cats. The other subgroups arise de novo and as results of recombination with an endogenous DNA feline sequence. Hence, there is very good evidence this virus is quite ancient, and may well have evolved more than one time over the last 10,000,000 years.

As the name 'oncovirus' suggests, it is a virus which causes cancer, however it also causes immunosuppression, allowing other diseases to take hold. It can also cause bone marrow suppression, with anaemia.

The virus is extremely fragile & quickly destroyed in the environment.

How is FeLV transmitted?

Large numbers of the virus are shed via saliva & respiratory secretions. Smaller amounts of virus are shed in the urine, faeces & milk. The virus is passed via mutual grooming, sneezing, nose to nose contact, sharing food bowls, in uterus, via the milk, bites & sharing litter trays. Young kittens are most susceptible to FeLV infection.

What does FeLV do?

Once the virus enters the body the virus replicates in the lymphoid tissue surrounding the site of the initial virus penetration. Having been infected, there are three possible outcomes;

1) The cat develops a transient viremia. The virus is present in the blood & saliva for less than 12 weeks. The cat develops neutralising antibodies which destroy the disease. The cats no longer infected & cannot transmit the disease to other cats. They don't become sick & have a normal life expectancy. This happens in approximately 33% of cases.

2) The cat develops a persistent viremia. The virus is present in the blood & saliva for over 12 weeks. The cat doesn't mount an effective immune response & is susceptible to many diseases which will prove fatal. Mortality ranges from 6 months & 3 years. This happens in approximately 33% of cases.

3) The cat develops a latent infection. They produce neutralising antibodies to destroy the virus, but the virus isn't extinguished completely & the virus persists in the bone marrow & T-cell lymphocytes. The cat typically doesn't develop diseases or cancers related to FeLV. The virus can be re-activated during times of stress or concurrent illness.

What are the symptoms of FeLV?

Clinical signs vary widely, depending on the disease type & which organs are involved. Some symptoms either caused directly or indirectly by FeLV include;
· Poor appetite & or weight loss
· Fever
· Apathy
· Enlarged lymph nodes
· Pale mucous membranes
· Gastrointestinal disorders
· Lymphosarcoma
· Secondary infections due to the weakened immune system
· Difficulty breathing
· Gingivitis/stomatitis

Around 80% of cats die within a year of infection, and almost all will die within 2-3 years.

How is FeLV diagnosed?

There are two types of test available.

(enzyme-linked immunosorbent assay) test can be performed in your veterinarian's surgery. It can detect an antigen known as p27 in whole blood, serum, plasma, saliva & tears of the cat. It is possible to get a false positive or a false negative. In the case of a positive from whole blood, a second test performed on plasma or serum is recommended.

IFA (immunofluorescence assay) which needs to be sent out to a laboratory. Testing detects antigen in leucocytes (white blood cells) or platelets.

How is FeLV managed?

There is no cure for FeLV& treatment of FeLV is usually targeted at managing FeLV related diseases, and also keeping the cat as healthy as possible. Your veterinarian will tailor treatment & care of the FeLV positive cat according to it's individual circumstances. Keeping your cat in a stress free environment, feeding a nutritious diet & avoiding exposure to disease are all important keys to helping a cat with FeLV. Treatments/management may include;

· Regular check ups with your veterinarian to carefully monitor your cat's health
· The veterinarian may recommend a different vaccination schedule for the FeLV positive cat
· Interferon may be prescribed by your veterinarian. Interferon is a natural protein released by cells which have been invaded by viruses & assist the immune response by inhibiting viral replication.
· AZT is an antiviral drug used in humans with HIV. It can produce quite severe side effects in cats. Your cat will need to be closely monitored by his veterinarian
· Administration of antibiotics where necessary for secondary bacterial infections
· Fluid therapy to treat dehydration
· Administration of vitamins & minerals
· Chemotherapy to manage lymphoma
· Keeping your cat indoors

Prevention of FeLV:

· To prevent exposure in the first place, it is advised you keep your cat either indoors or contained within a cat enclosure.
· There is a vaccine for FeLV. This is recommended for cats who are at high risk of exposure to the virus. No vaccine is 100% effective, so it should not be presumed that once the cat is vaccinated it is completely safe from infection.
· Avoid having FeLV positive & negative cats together.
· Before introducing a new cat to your home, always test it for FeLV.