Feline
Leukemia

Feline Leukemia is a viral disease of cats.  It has been estimated that feline leukemia is responsible for more suffering and sickness in cats than any other single disease.  Although it has the word leukemia in it's name, most cats with the disease do not have leukemia.  Feline Leukemia, abbreviated FeLV, is a complex disease with a complex cause and a complex set of symptoms.  What follows is my attempt at simplifying a complex topic with out losing accuracy.

FeLV is caused by a virus.  Some viruses are merely annoying, like the influenza virus that gives us the flu, or the papilloma virus that gives us warts.  Other viruses are much more sinister.  Take HIV, the human immunodeficiency virus.  It gives us AIDS.  It is incurable and deadly.  I didn't choose the HIV at random, by the way.  HIV is a member of a family of viruses called retroviruses.  Far from being a thing of the past, retroviruses are very much a thing of the present, and cause serious disease in both humans and cats.  That's right, FeLV is a retrovirus too, just like HIV.  Not coincidentally, FeLV causes a whole spectrum of diseases, all relating somehow to immune system failure, just like it's cousin HIV.  In fact, we'd call FeLV "Feline AIDS" except for the fact that there is another cat virus, feline immunodeficiency virus, or FIV,  that is even more closely related to HIV that has taken that nick-name.  But more on FIV later.

Cats that become infected with FeLV do not immediately start showing symptoms.  As with AIDS, there is a latent period of varying length, months to years, in which the infected cat will remain perfectly healthy.  However, these cats are able to spread the virus even though they do not show any symptoms.

Like HIV, FeLV causes immune system failure.  It does this by attacking the cells that make up our immune system.  Without a fully-functioning immune system, the body becomes susceptible to every little bug that comes around.  In cats, we see a mind-boggleingly vast array of symptoms in cats with FeLV.  Anything is possible.  We start to strongly suspect FeLV whenever we see cats with chronic infections, long-term illnesses, or bad periodontal disease.  Some cats with FeLV will develop cancer as well.

If you pick a healthy cat at random, about 3 in 100 will have FeLV.  However, if you pick from a group of  stray cats, about 1 in 10 will be infected.  And if you choose from a group of sick cats, more like 1 in 5 will be infected.  About 1 in 5 cats with periodontal disease or FORL's will have FeLV too.

FeLV is similar to AIDS in that it is not spread by casual contact.  FeLV is a fragile virus that does not survive in the environment more than a few minutes.  There is no danger that cats can be exposed to FeLV in veterinary clinic waiting rooms or exam rooms, or in cages, or at cat shows unless direct contact is made with a positive cat who is shedding virus. Transmission of FeLV requires intimate moist contact. The most common route is contact with infected saliva through grooming, licking, fighting, biting, and sharing food dishes and litter pans. FeLV can also be transmitted through a blood transfusion, so all cats who are blood donors are screened for FeLV. Kittens can be infected by their mother before birth or during nursing after birth.

The American Association of Feline Practitioners (AAFP) has published recommendations for FeLV testing. The AAFP is a professional association of veterinarians that focuses on the health needs of cats.  The guidelines state that the FeLV status of all cats should be known because FeLV is responsible for the illness and death of more cats than any other disease condition. Testing and identifying positive cats is the mainstay of FeLV control and is not replaced by vaccination. 
In particular, testing is recommended for cats who:

1.     Have had a recent exposure to a known FeLV positive cat.  This includes all cats being treated for an abcess, since most abcesses are caused by bite wounds, often from a stray cat (remember the  one-in-ten chance that a stray cat will have FeLV?)

2.     Are ill, including dental disease.  About 1 in five sick cats will have FeLV.

3.    Are new.  Any new kitten or cat should be tested before being added to a household with resident cats. Even if the household does not already have resident cats, new pets should be tested because the emotional bond that forms between owners and pets justifies knowing any future threats to the pet's health.

What do we do with cats that test positive for FeLV?      If your cat is here in the Clinic because he or she is sick, knowing whether there is FeLV involved can be very important in planning treatment.  But what about the healthy cats that test positive?  While FeLV is not curable, many cats live for years without any symptoms. 

For starters, it is important to re-test healthy cats if they test positive.  No test is perfect, and a positive result should always be corroborated.  Also, some cats will become infected with FeLV, but will successfully defeat the disease and become negative months later.

For healthy cats with confirmed FeLV infections, there are two goals.  One is to keep the infected cat as healthy as possible.  The other goal is to keep them from spreading the disease.  Keeping the infected cat healthy involves good nutrition, regular veterinary examinations (every 6 to 12 months), and appropriate vaccinations (but not FeLV).  Keeping them from spreading their disease is harder.  It is vital that they not be allowed outdoors where they could fight with non-infected cats.  A good resource for converting your outdoor cat to an indoor cat is found here.  For cats who share a house with an infected cat, it is important to minimize the sharing of food and water dishes, litterboxes, etc.  FeLV can be spread by grooming as well, so it can be very difficult to control the spread of FeLV within a household unless the two cats are physically separated.

The best way to protect your cat from FeLV is to vaccinate against it.  The vaccine against FeLV is a pretty good vaccine.  Some vaccines are excellent, and protect nearly 100% of the individuals who get vaccinated.  Other vaccines are only fair, like the Lymes disease vaccine for dogs, and protect 50% or 60% of the individuals that get vaccinated.  The FeLV vaccine rates pretty good, and protects about 80% of the cats who get vaccinated.  While it is not 100%, it is much better than nothing, and is a good thing to do in my opinion.

The second-best way to protect your cat from FeLV is to spay or neuter.  Tomcats especially lead a "high-risk lifestyle," complete with roaming and fighting.  Neutering will dramatically decrease these high-risk behaviors.  A third way to protect your cat, the pro's and con's of which are debatable, is to confine you cat strictly to the indoors.