Feline Leukemia Virus (FeLV)

Home » Feline Leukemia Virus (FeLV) » Overview, Risk Factors, Transmission

Overview

Feline leukemia virus (FeLV) infection is responsible for more deaths among cats than any other infectious disease. The virus affects domestic cats and occurs in some wild felines as well.

Types of FeLV
There are three main types of feline leukemia virus: FeLV-A, FeLV-B, and FeLV-C. FeLV-positive cats can be infected with one, two, or all three types:

• FeLV-A occurs in all FeLV-infected cats and causes severe immunosuppression (weakened immune system).
• FeLV-B occurs in about 50% of all FeLV-infected cats and causes more neoplastic disease (i.e., tumors and other abnormal tissue growths) than cats infected only with FeLV-A.
• FeLV-C occurs in about 1% of FeLV-infected cats and causes severe anemia.

After the initial infection, the virus replicates in the tonsils and pharyngeal lymph nodes (the pharynx is the muscular tube in the neck). Then it spreads via the bloodstream to other parts of the body, especially the lymph nodes, bone marrow, and intestinal tissue, where it continues to replicate. Viremia, the presence of virus in the blood, usually shows up 2 to 4 weeks after the initial infection.

Incidence
FeLV is one of the most devastating feline diseases worldwide. In the United States, FeLV infects about 2% to 3% of all cats.

Risk Factors

Sick cats are four times more likely than healthy cats to be infected with FeLV. Researchers estimate that about 50% of cats with severe bacterial infections, and 75% of cats with toxoplasmosis, a protozoan disease, also have FeLV infections.

Males are 1.7 times more likely to be infected than females, and younger cats are more susceptible to infection than older cats. FeLV is found mostly in cats from 1 to 6 years old; the average age is 3 years.

Outdoor cats are more likely to be infected with FeLV. Less than 1% of healthy indoor cats in the United States are infected with FeLV, compared to 1% to 2% of healthy outdoor cats, and more than 13% of sick stray cats. FeLV is more common in multicat households than in single-cat households, especially when cats go outdoors.

Transmission
FeLV usually spreads through infected saliva. It can also spread through infected urine, tears, and feces, and through an infected mother to her kittens during gestation and nursing. Twenty percent of FeLV-positive mothers pass the virus to their kittens. Methods of transmission include the following:

• Bite wounds from infected cats (more common among outdoor and indoor-outdoor cats)
• Blood transfusions
• Mouth and nose contact with infected saliva or urine
• Mutual grooming
• Nose-to-nose contact
• Shared food dishes and water bowls
• Shared litter trays
• Sneezing

Immune cats that are temporarily viremic may or may not shed the virus (i.e., spread it through their saliva, tears, urine, feces) during the few weeks that it's in their blood. All persistently viremic cats spread the virus through their saliva, tears, urine, and feces for the rest of their lives. In normal conditions, FeLV survives less than a few hours outside of a cat's body.

Veterinarian researchers generally agree that FeLV cannot be transmitted to humans. Some studies have shown a correlation between certain human leukemia and exposure to FeLV-infected cats, but this has not been proven.

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