* Editor’s note: This column originally ran in 2009.
Feline leukemia virus (FeLV) is a significant cause of health issues in cats. Understanding the nature of the virus and the disease process provides the best way to prevent or manage the disease.
FeLV is a retrovirus, meaning that its genetic code gets inserted into the DNA of infected cats. This virus then replicates within the cat’s cells and can be released systemically.
The main form of transmission of the virus from one cat to another is through saliva, although other body fluids may carry the virus. Typically, prolonged contact with an infected cat is needed to cause virus transmission, although bite wounds can also be infectious. In some cases, infected cats may pass the disease through the placenta or milk to their offspring. Cats with FeLV may have the ability to transmit the virus whether they show any evidence of the disease or not.
The changes in the body caused by FeLV can be put into two main categories: directly causing leukemia/lymphoma, and indirectly causing secondary processes.
Leukemia in general is a cancer of the white blood cells, causing abnormal development of the cells in the bone marrow which are then released into the bloodstream. While FeLV can cause leukemia, not all leukemias in cats are caused by the virus. Lymphoma is a cancer specifically of lymphocytes, a type of white blood cell. Despite the name of the virus, FeLV is much more likely to cause lymphoma than leukemia in cats.
The symptoms associated with lymphoma depend on the location of the abnormal lymphocytes. Lymphoma may be centered in the chest, kidneys, spine, gastrointestinal system, lymph nodes, or a combination of the above. Outwardly, leukemia and lymphoma may manifest as general illness: fever, decreased appetite, lethargy, etc.
FeLV also indirectly causes non-cancerous changes in the body. These may include anemia, neurological problems, vomiting, and diarrhea. Female cats that have not been spayed may become infertile due to the virus. Cats’ immune systems can become suppressed, leading to secondary infections.
Some cats may create enough of an immune response to the FeLV that they effectively suppress the virus. While the virus’s genetic material still permanently lives within the cat, it is unable to reproduce. These cats are usually healthy and cannot infect others. However, those cats that do not suppress the virus and develop any of the above problems will have a significantly decreased life expectancy. There is no direct treatment for the virus. Lymphoma can be treated with chemotherapy, but only supportive care can be offered for other forms of the disease.
There is a quick blood test that is available at most veterinary clinics to test cats for the presence of FeLV. This test is recommended for all cats with unknown history of vaccination and disease exposure, such as feral cats and kittens. It is also recommended for other circumstances, such as when a cat has been in a fight with another cat of unknown disease status.
Feline leukemia vaccines are available and are recommended for cats who spend time outdoors or who live indoors with another cat with the virus. It is typically given as an initial series of two injections, followed by boosters either yearly or every three years, depending on the type of vaccine.
All cat owners are encouraged to speak with their veterinarian about the risk of FeLV for their cats, and whether testing and/or vaccination are appropriate.
— Keith Rode is a veterinarian at Woodland Veterinary Hospital and a graduate of UC Davis. For more information, call 530-666-2461.