Feline Leukemia Virus Infection

Basics
Overview
-A retrovirus that causes inability to develop a normal immune response (known as "immunodeficiency") and development of tumors in domestic cats
Genetics
-No genetic susceptibility to infection by feline leukemia virus (FeLV)
Signalment/Description of Pet
Species
-Cats
Breed Predilections
-None
Average Age and Range
-Number of cases highest between 1 and 6 years of age
-Average - 3 years of age
Predominant Sex
-Male-to-female ratio-1.7:1 (that is, males are 1.7 times more likely to have feline leukemia virus infection than are females)
Signs/Observed Changes in the Pet
-Onset of feline leukemia virus-associated disease-usually occurs over a period of months to years after infection
Associated diseases-may be related to inability to develop a normal immune response (immunodeficiency) or to development of tumors or cancer
-Clinical signs of FeLV-induced inability to develop a normal immune response (immunodeficiency) cannot be distinguished from those of feline immunodeficiency virus (FIV)-induced immunodeficiency
-Signs depend on the type of disease (inability to develop a normal immune response [immunodeficiency] or tumor/cancer) and occurrence of secondary infections
-Enlarged lymph nodes (known as "lymphadenomegaly")-mild to severe
-Upper respiratory tract disease-inflammation of the nose (known as "rhinitis"), inflammation of the moist tissues of the eye (known as "conjunctivitis"), and inflammation of the cornea (known as "keratitis"; the "cornea" is the is the clear outer layer of the front of the eye), seen in 18% of cases
-Persistent diarrhea
-Inflammation of the gums (known as "gingivitis"), of the mouth (known as "stomatitis"), and/or of the tissues surrounding and supporting the teeth (known as "periodontitis")
Long-term (chronic), nonresponsive or recurrent infections of the external ear and skin; abscesses
-Fever and wasting (seen in 42% to 53% of cases)
-Lymphoma (a type of cancer that develops from lymphoid tissue, including lymphocytes, a type of white-blood cell formed in lymphatic tissues throughout the body)-most common FeLV-associated cancer
-Leukemia
-Fibrosarcomas (cancer that develops from fibrous tissue)-in pets co-infected with mutated sarcoma virus; most frequently in young cats
-Disorders usually affecting the nerves to the legs and paws (known as "peripheral neuropathies"); progressive wobbly, incoordinated or "drunken" appearing gait or movement (known as "ataxia")
Causes
-Cat-to-cat transmission-bites; close casual contact (such as grooming); shared dishes or litter pans
-Transmission of the virus from the mother cat (known as a "queen") around the time of birth-fetal and newborn kitten death from 80% of affected queens; transmission across the placenta or through the milk in at least 20% of surviving kittens from infected queens
Risk Factors
-Age-kittens are much more susceptible to infection than are adults
-Male-result of behavior
-Cat allowed outside; free-roaming cats
-Multicat household

Treatment
Health Care
-Outpatient for most cats
-Inpatient-may be required with severe secondary infections, low red-blood cell count (known as "anemia"), or extreme weight loss with muscle wasting (known as "cachexia") until condition is stable
-Blood transfusions-emergency support; multiple transfusions may be necessary
-Management of secondary and opportunistic infections-primary consideration; "opportunistic infections" are infections caused by organisms that usually do not cause disease, but are able to cause disease because the cat's body and/or immune system has been weakened, in this case by the feline leukemia virus infection
-Supportive therapy (such as fluids and nutritional supplements) may be useful
Activity
-Normal
Diet
-Normal
-Diarrhea, kidney disease, or long-term (chronic) wasting-may require special diet
Surgery
-Biopsy or surgical removal of tumors
-Dental cleaning, tooth extraction, biopsy of the gums
Medications
-Medications presented in this section are intended to provide general information about possible treatment. The treatment for a particular condition may evolve as medical advances are made; therefore, the medications should not be considered as all inclusive
-Zidovudine (Retrovir)-antiviral agent; may lead to clinical improvement, but does not clear virus
-Medications to alter the immune response (known as "immunomodulatory drugs")-may alleviate some clinical signs; interferon (Roferon) may increase survival rates and improve clinical status; Propionibacterium acnes (ImmunoRegulin); acemannan (Carrisyn)
-Mycoplasma haemofelis infection-suspect in all cats with low red-blood cell counts due to the destruction of red-blood cells, in which the body is producing new red-blood cells (known as "regenerative hemolytic anemia"); oxytetracycline or doxycycline; short-term use of steroids, administered by mouth, if needed
-Lymphoma (a type of cancer that develops from lymphoid tissue, including lymphocytes, a type of white-blood cell formed in lymphatic tissues throughout the body)-management with standard combination chemotherapy protocols; periods of remission average 3-4 months; some cats may remain in remission for much longer
-Blood disorders or disease and leukemias-less responsive to medical treatment; for low red-blood cell count (anemia), try erythropoietin (Epogen); for low neutrophil count (known as "neutropenia"), try Neupogen
-Yearly vaccination for respiratory and intestinal viruses with inactivated vaccines recommended

Follow-Up Care
Patient Monitoring
-Varies according to the secondary infections and other manifestations of disease
Preventions and Avoidance
-Prevent contact with feline leukemia virus--positive cats
-Quarantine and test incoming cats before introduction into households currently with one or more cats
Vaccines
-Several commercial feline leukemia virus vaccines are available
-Test cats for FeLV before initial vaccination; if prevaccination testing is not done, advise clients that the cat may already be infected
-Vaccinate kittens at 8-9 weeks and 12 weeks of age; administer booster FeLV vaccine at 1 year of age; revaccinate every 2-3 years thereafter

Possible Complications
-Exposure of non-feline leukemia virus-infected cats to infection
-Development of disease related to inability to develop a normal immune response (immunodeficiency)
-Development of tumors or cancer
-Death

Expected Course and Prognosis
-Cats that persistently have feline leukemia virus in their blood (known as "FeLV viremic cats")-more than 50% succumb to related diseases within 2-3 years after infection

Key Points
-Keep feline leukemia virus-infected cats indoors and separated from FeLV-negative cats, to protect them from exposure to secondary disease-causing agents and to prevent spread of FeLV to other cats
-Good nutrition is important
-Control secondary bacterial, viral, and parasitic infections