Cats are prone to catching a number of infections. Of particular interest is the number of chronic viral infections to which they are susceptible. Feline Leukemia Virus or FeLV is one of the most notorious.

How do cats get the Feline Leukemia Virus? How is it spread?

According to the Cornell Feline Health Center, about 2 to 3 percent of American cats are infected. The Leukemia virus is shed in the saliva and nose discharges of an infected cat. The virus is relatively unstable and cannot live outside an infected cat for more than a few hours in a dry environment. It is spread from cat to cat via shared food and water bowls and close contact, i.e., grooming. FeLV can be transmitted from a mother cat to her kittens in utero, through mother-kitten contact, or through her milk. Cat bites are another source of infection. Kittens are especially susceptible to contracting FeLV. After four months of age, natural resistance develops in many cats. Adults are relatively resistant to infection with FeLV.

What happens if cats get it?

When a cat first contracts FeLV, they are termed “viremic,” meaning there is virus in the bloodstream. The viremic stage may progress to:

1. Persistent infection. Some cats, once infected, become persistently infected within weeks of exposure. Virus is found in their blood and bone marrow. This is especially the case in young kittens exposed to FeLV.
2. Sequestered infection. Other cats will contract the virus and then sequester it (hold it inactively) in their bone marrow or other tissues for a variable length of time. Later, if the cat is stressed or treated with immune suppressing medications, the leukemia virus can erupt and cause active disease.
3. No disease. There are a proportion of cats exposed to the virus that develop immunity and clear the virus from their system, leaving no trace of FeLV in their blood, bone marrow, or other tissues. It turns out after careful study that many of these cats are really latent carriers of the infection, but some of these cats with deeply integrated sequestered virus can live a healthy life without ever developing disease symptoms.

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