The Deadliest Catch – Feline Leukemia Virus

What is Feline Leukemia Virus (FeLV)?

Feline Leukemia virus is an infectious virus of cats that invades and replicates in various cells, including those of the immune system, and blood forming tissues. Most commonly, infection of the virus often results in cancer, suppression of the immune system, and the development of other diseases. Feline Leukemia virus is usually fatal. Approximately 80-90% of infected cats will die within 3 to 4 years.

How is FeLV transmitted?

The most frequent method of transmission is through direct contact between cats. FeLV positive cats shed large quantities of the virus in their saliva, nasal secretions, urine, and feces. Transmission usually occurs when prolonged close contact occurs between infected and susceptible cats. Close contact activities include:

  • Mating
  • Mutual grooming
  • Sharing of litter trays and food bowls
  • Bite wounds from an infected cat

Another source of transmission can be from an infected mother cat to her kittens, either before they are born or while they are nursing. However, it is more likely that an infected un-spayed female will become infertile or there is pre-natal death of the kittens.

How common is FeLV and who is at risk?

Approximately 1 to 3% of all cats are infected with FeLV. The prevalence of infection varies greatly depending on age, health, environment, and lifestyle. Cats at greatest risk of infection are those that may be exposed to infected cats, especially those cats living in colonies where there is close contact between individuals. Cats that have the highest risk of infection Include:

  • Cats living with infected cats or with cats of unknown infection status
  • Cats allowed outdoors unsupervised, where they may be bitten by an infected cat
  • Kittens born to infected mothers


What happens when a cat is exposed to FeLV?

Not all cats exposed to FeLV will become persistently infected with the virus. Approximately 30% of the cats exposed to the virus will be able to mount an immune response that is successful in eliminating the virus. However, there is a period of time before the virus is eliminated that the virus is replicating in the cat’s cells. During this period of time there may be cell changes that lead to disease later in life. 70% of cats are unable to mount an immune response. These cats become permanently infected with the virus, and are primarily responsible for the transmission of FeLV to other cats. It may be many months to years between the initial infectionand the onset of related clinical disease problems. Often the infected cat’s health will progressively decline or have recurrent illnesses interspersed with periods of relative health. Signs of disease due to infection include:

  • Loss of appetite
  • Progressive weight loss, followed by severe wasting during late stages of disease
  • Poor coat condition
  • Lymph node enlargement
  • Constant fever
  • Pale gums and mucous membranes
  • Inflammation of gums and mouth
  • Upper respiratory tract, urinary bladder, and/or skin infections
  • Diarrhea
  • Neurological disorders, seizures, and behavior changes
  • Eye conditions
  • Abortion of kittens or reproductive failures in un-spayed female cats


How can FeLV be diagnosed and is there any treatment?

A simple blood test can be performed that will detect viral proteins in the blood. Although accurate and reliable, a second test may be recommended eight to twelve weeks after the first test to confirm persistent infection. There is currently no cure or treatment that will eliminate the FeLV virus from the body. Most FelV positive cats can be treated symptomatically by treating the secondary infections that arise. However, most FeLV positive cats will either die or be euthanized due to diseases related to their in FeLV infection.

How can I protect my cat from becoming infected?

It is recommended that all cats that go outdoors or come in contact with potentially infected cats be vaccinated. The Purevax Feline Leukemia vaccine is a highly effective vaccine that does not contain additives or adjuvants, thus reducing the risks of injection site reactions and chronic inflammation. Prior to vaccination, all cats should be tested for FeLV. In addition to routinely vaccinating your cat for FeLV, some other simple steps for keeping your cat safe include:

  • Keeping cats indoors.
  • Keeping cats from coming in contact with known FeLV infected cats, potentially infected cats, or cats with an unknown vaccination history.
  • Supervise cats when outside or provide a safe enclosure.
  • House infected cats separately from un-infected cats.
  • Do not share food and water bowls or litter boxes of infected cats with uninfected cats.