FeLV

Feline Leukemia Virus

Feline leukemia virus (FeLV) is a virus that is transmitted between animals through salivary contact with other cats; known routes of transmission include biting, licking, and grooming. Infected queens can infect kittens prior to birth or will suckling. However, virus contact does not assure infection, and infection does not ensure persistent viraemia or disease. The four possible outcomes of exposure are listed below.

The cat mounts an immune response; some immunity is produced, making the cat resistant to future infections for an undetermined period of time.
The virus survives within the bloodstream leading to persistent infection.
Latency: The cat does not produce immunity, but it does not become persistent viraemia. This is a transient stage that lasts an average of 30 months. Ultimately, it results in virus neutralization or persistent viraemia.
Immune carrier: The whole virus is sequestered in epithelial tissue and is replicating, but it does not leave the cells due to antibody production.

Once introduced into the cat, the virus progresses through various tissues. The ability of the immune system to halt this progression determines the ultimate outcome. The virus produces several proliferative diseases (lymphosarcoma, leukemias), several degenerative diseases (nonregenerative anemias, thymic atrophy, panleukopenia-like syndrome, stillbirths, abortions), and immunosuppression. Clinical signs vary widely depending on the disease type and the organs involved. Test results vary depending on the form of disease present and the target organs involved. For example, over 90% of cats with anterior mediastinal lymphosarcoma are virus positive; less than 50% of cats with alimentary lymphosarcoma are virus positive. Household disinfection to kill the virus is easily accomplished. Without treatment, the virus is gone within a week.

The virus can be removed from a multicat household by a test and removal program. New cats introduced into a household should be tested for FeLV prior to admission.

No effective antiviral treatment is available for FeLV infected cats.

The clinical signs of a cat with an FeLV related illness vary depending on the type of related disease and the organ system infected.

Vaccination is recommended for all cats that have exposure to free-roaming cats or to known FeLV infected cats. Exposure produces solid immunity in 80-90% of vaccinated cats, but the rate is lower when cats are continuously exposed to infected cats.

Because the FeLV causes such a wide variety of diseases, any seriously ill cats should be tested for it. However, its presence does not necessarily mean that it is the cause of the cat's current illness or that the cat is contagious.

Cats that are infected with the FeLV but show no clinical signs may remain asymptomatic for several years. They may be healthy, but they can be contagious to other cats. Cats with any FeLV disease have a guarded prognosis.