FeLV: a lethal threat: but luckily, a positive diagnosis of this viral infection is not necessarily a death sentence. Here's why.(Disease)

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Among all causes of severe feline disease, none is more prevalent than feline leukemia virus (FeLV), a submicroscopic organism associated with the illness and death of more cats worldwide than any other infectious agent. This virus--which is spread through the urine, saliva, nasal secretions or milk of infected animals--is currently recognized as the chief causative agent of fatal infectious disease among U.S. domestic cats.

According to Fred Scott, DVM, PhD, professor emeritus of virology at Cornell University's College of Veterinary Medicine and the founding director of the Cornell Feline Health Center, it is estimated that FeLV is present in two percent to four percent of the overall cat population in America. However, he says, the infection rate can vary significantly among specific feline subpopulations, noting that FeLV is especially common among cats that spend a good part of their time outdoors and are thus more likely to come in contact with infected animals that are shedding the virus.

"Depending on whether you're looking at indoor or outdoor cats," he points out, "the number of infected animals can range anywhere from a fraction of a percent to 15 or 20 percent." The rate tends to be most noticeably high in cats that are already ill and in those that are very young.

slow-Acting organism

Virologists classify FeLV as a lentivirus, a slow-acting organism that is in the same viral family as the potentially deadly feline immunodeficiency virus (FIV). It is also classified as a retrovirus--a type of virus that converts its genetic blueprint (single-stranded RNA) into double-stranded DNA within the nucleus of a host cell by the use of the enzyme reverse transcriptase. The DNA then produces all the necessary new viral RNA to make new viral particles.

"Following exposure, the virus replicates in the local lymphatic areas--in the superficial cells of the tonsils, for example," explains Dr. Scott. "This is followed by a transient viremia [virus in the blood], with the virus spreading systemically over a few days, reaching other tissues in the body. If the cat's immune response is sufficient, that's as far as the virus goes. But if the immune response does not control it, the virus will eventually end up in the bone marrow and will infect other cells there.