Feline leukemia is a very serious disease of cats. Once contracted, the disease is usually invariably fatal, as no cure is currently available. Feline leukemia was a much greater problem in the past before effective vaccination protocols were discovered. However, despite these advances, feline leukemia remains problematic, and is still one of the top causes of death in cats. In this article, feline leukemia will be defined and explained indepthly,
with detailed information regarding clinical signs, diagnosis, treatment options, and prevention.
Feline leukemia is caused by feline leukemia virus, which is a retrovirus. The term "leukemia" refers to cancer of the white blood cells, however, the virus causes a clinical scenario much broader than cancer. In fact, the vast majority of secondary disease cause by the feline leukemia virus are not cancer. The Non-Cancerous Diseases include a variety of rather unrelated diseases. Anemia, abortion, arthritis, and immune suppression are examples. When the immune system is suppressed, the cat becomes susceptible to many diseases it would ordinarily resist and mild diseases, such as respiratory infections, may become fatal.
Retroviruses, as a general rule, do not survive well in the environment outside the host. For this reason, the transmission of feline leukemia requires intimate contact between cats. As a result, the most common modes of transmission are bites wounds, copulation, and from mother to kittens prior to birth.
Feline leukemia is diagnosed by a simple blood test. Most veterinary clinics have a fast feline leukemia "snap test" that is performed in-house. This test utilizes technology called ELISA testing, and is quite accurate, with few incidences of false positives and negatives. This test will show positive even in the early stages of infection, as early as 72 hours following infection with feline leukemia virus. For this reason, retesting in the future will sometimes show negative, as the feline immune system has the ability to clear the virus in the early stages of infection.
Anther widely used test for feline leukemia is called IFA. Blood samples for IFA have to be sent to a lab for testing. The IFA test will usually only show positive in cases of advanced to late stage disease. Therefore, a with cat that shows positive for feline leukemia, routine retesting to confirm disease is almost always positive again.
There are a number of scenarios that can ultimately play out should a cat become infected with feline leukemia virus. This can be quite variable and will depend upon: amount of virus at time of infection, the particular strain of the virus, immune system status at the time of infection, and age of the cat. The possible outcomes of infection with feline leukemia virus based on all of these factors are best summarized below.
The first possible outcome of leukemia infection is that the cat mounts a sufficient immune response and clears the virus from its system. During this viral challenge, the cat may experience mild signs of disease, such as poor appetite, em;arged/painful lymph nodes, and lethargy for anywhere from 2 to 12 days. Once the virus is successfully cleared, the patient will retain strong immunity to the virus. This occurs more commonly in adults than in kittens.
The second possible outcome of feline leukemia infection is permanent infection with the disease. 50 % of these cats die within two to three years of infection. Only a small percentage survive past 4 years.
The third possbile outcome of feline leukemia infection is patient infection. In this scenario, the virus incorporates a copy of its DNA into the DNA of the host cat. The cells in which this happens may later be tranformed into cancer cells or function abnormally. The patient can remain clinically normal for many years.
The final possible outcome of feline leukemia virus infection is a quite rare and only occurs in 1% - 2 % of infected cats, a status called immune carrier. In this case, the virus remains hidden in tissue cells of the host. The virus continues to replicate, but is kept at bay by the host's immune system, unable to spread to other tissue cells. This type of patient remains clinically normal but can spread feline leukemia to other cats.
Treatment for feline leukemia is supportive and often non-specific. The secondary disease maifestations, such as infections need to first be addressed. Then, treatment is geared toward boosting the patients immune system, Some feline leukemia cats respond to treatment with the immune messenger molecule, interferon. This will sometimes support the cat's immune system enough to live with reasonable quality, but support often does not last very long - longevity of interferon effect is quite variable. Cats that have cancer secondary to the disease have to be euthanized the vast majority of the time.
In the end, the best way to deal with feline leukemia is to prevent infection in the first place. Any cats that go outside, live with cats that go outside, or live with cats that are infected with feline leukemia, should be vaccinated regularly against the disease. Several commercial vaccines are available that are very effective in preventing feline leukemia. See our Vaccine Info page for more on this.
