Feline leukemia virus is a viral disease of domestic cats that impairs immune system function and causes some types of cancer. It is caused by a retrovirus that cats shed in high quantities in saliva and nasal secretions, but it is also found in the urine, feces and milk of infected cats. Cat-to-cat transfer of the virus may occur from a bite wound, during mutual grooming and, rarely, through sharing litter boxes and feeding dishes. It can also be transmitted across the placenta and milk.
Common name: Feline leukemia virus infection (FeLV)
Scientific name: Retrovirus (Gammaretrovirus genus)
Feline leukemia virus infection is responsible for more cat deaths than any other infectious disease. Cats at greatest risk of infection are those that are exposed to infected cats, either via prolonged close contact or through bite wounds. Cats living with infected cats or cats of unknown infection status are at risk.
In addition, cats allowed to roam outdoors, where they may be bitten by an infected cat, and any kittens born to infected mothers could contract the disease. Males are 1.7 times more likely to be infected than females, and younger cats are more susceptible to infection than older cats. Feline leukemia virus infection is found most often in cats from 1 to 6 years old. All breeds of cats are equally at risk.
Feline leukemia is one the most devastating feline diseases worldwide, and the incidence of infection varies greatly depending on each cat's age, health, environment and lifestyle. It is estimated that 2 percent to 3 percent of healthy-appearing cats are infected with the virus. Approximately 25 percent to 50 percent of the healthy-appearing cats living in infected multicat households and catteries are infected. Rates rise significantly in cats that are ill, very young or otherwise at high risk of infection.
Feline-leukemia-virus-infected cats are found worldwide.
Clinical signs (primary, most to least frequent, scientific term, synonyms)
Loss of appetite, Anemia, Weight loss, Persistent diarrhea, Enlarged lymph nodes, Fever, Inflammation of the gums (gingivitis) and mouth (stomatitis), Infections of the skin, urinary bladder and upper respiratory tract.
Clinical signs (secondary, most to least frequent, scientific term, synonyms)
Chronic, recurring infections, Jaundice (a yellowing of the skin, whites of the eyes, mucous membranes and body fluids due to liver dysfunction), Neuropathies (seizures, paralysis, blindness, behavioral changes, loss of balance), Cancer, Eye conditions (anisicoria ‚Äì uneven pupils), Spontaneous miscarriage or other reproductive failures.
Cause (scientific, common term)
Retrovirus (Gammaretrovirus genus).
Organ systems affected (most to least affected)
Immune, Hematologic, Lymphatic, Gastrointestinal, Respiratory, Neurological, Urinary, Reproductive, Eyes, Skin.
Complete medical history, Thorough physical examination, ELISA test (veterinary screening test for FeLV), Complete blood count, Serum biochemistry tests, Urinalysis, Chest and abdominal radiographic views, Fine needle aspiration on enlarged lymph nodes or solid tumors, Bone marrow microscopic evaluation in cats with anemia, low white blood and platelet counts, IFA (confirmatory test for FeLV), Cerebrospinal fluid analysis (for cats with neurological symptoms).
FIV (feline immunodeficiency virus infection), Other infections (bacterial, parasitic, viral or fungal), Non-viral cancerous diseases.
Feline leukemia (FeLV) is a viral disease of domestic cats caused by a retrovirus that impairs immune system function and causes some cancers. Feline-leukemia-infected cats are found worldwide, with nearly 2 percent to 3 percent of cats in the United States infected. Males are infected more than females, and younger cats (1 to 6 years old) more than older cats.
The virus is shed through bodily fluids. Virus in high quantity can be found in saliva and nasal secretions but is also found in urine, feces and milk. It is transmitted through bite wounds, during mutual grooming, across placenta and milk and, rarely, through sharing litter boxes and feeding dishes. Cats with little exposure to other cats are at significantly less risk of getting this disease. Other cats become carriers of the virus without themselves showing symptoms. These cats then spread the virus to other cats.
Symptoms of infection include loss of appetite, slow, progressive weight loss followed by severe muscle wasting, poor coat condition, enlarged lymph nodes, persistent fever, pale and inflamed gums, infections of the skin and urinary bladder and upper respiratory tract, persistent diarrhea, seizures, behavior changes, eye conditions and miscarriage of kittens.
Always give medications as prescribed by your veterinarian. Provide high-quality nutrition and schedule regular follow-up medical visits. Prevent exposure to FeLV by keeping cats indoors and spaying/neutering to decrease roaming and fighting. Test all cats in the household and separate those with FeLV. Vaccinate ‚Äúat-risk‚Äù cats against FeLV, including outdoor cats, breeding cats and cats living in multicat households.
Veterinarians use either the ELISA or IFA blood test to diagnose feline leukemia virus. A complete medical history, a physical examination, blood work and a urinalysis will also be done. Once diagnosed, the veterinarian will develop a treatment plan.
If a cat has no symptoms, no treatment may be recommended. There is no effective treatment that will eradicate established FeLV infection. Supportive care is the treatment goal and may include antibiotics, nutritional support, fluid therapy, parasite control, blood transfusions, cancer therapy and antiviral drugs. If a FeLV-induced disease is present, treatment will be necessary.
The diagnosis and treatment of feline leukemia virus is made by a veterinarian. Treatment is focused on relieving pain and discomfort. Vaccines can protect cats from contracting FeLV, but none are 100 percent effective. Vaccinations are recommended for outdoor cats, show cats, boarded cats and cats in multicat households.
Cats should be tested and determined to be FeLV-negative before they are vaccinated. Cats kept entirely indoors may not need to be vaccinated against FeLV. Discuss this with a veterinarian.
Seventy percent of FeLV-infected cats develop immunity and may live a normal life. Some cats with initial immunity can become ill months later, when stressed or medicated with immunosuppressant drugs. Cats with severe illness have a worse prognosis. After a FeLV-infected cat dies, the house should be thoroughly disinfected, and pet supplies should be discarded. Wait 30 days before adopting a new pet.
Tilley, L.P., and Smith, F.W.K. Feline Leukemia Virus Infection. In: The 5-Minute Veterinary Consult, 3rd Ed. Baltimore: Lippincott Williams & Williams, 2004; 464-465.
American Association of Feline Practitioners and the Cornell Feline Health Center. Feline Leukemia Virus. In: http://www.vet.cornell.edu/fhc/brochures/felv.html. Ithaca: Cornell University, College of Veterinary Medicine, 2004; 1-4.
Geruza Paiva, DVM
Steven Hansen, DVM, MS, MBA
© 2007. The American Society for the Prevention of Cruelty to Animals (ASPCA)