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Breeding & Showing Cats

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Breeding & Showing Cats

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Feline Leukemia Virus (FeLV)

As we swap kittens and breedings, we often worry about ringworm, intestinal parasites, and upper respiratory viruses. But how often do we remember the silent, but oh so deadly, Feline Leukemia Virus (FeLV)? We assume that the cattery we are sharing with is FeLV negative, but is it really? Do we all think we are negative because we’ve had no “outbreaks” of symptomatic cats?

About Feline Leukemia Virus

This insidious disease had been slowly creeping into our catteries for decades before the virus was isolated in 1964 and a test developed in 1969. Those who have been around for a while, will remember the horrors of the ‘70’s and early ‘80’s when test and euthanize was the means to eradicate FeLV from purebred catteries. Many catteries and breeding lines were decimated, never to recover.

Due to testing and vaccinating, the incidence of FeLV in the general cat population has decreased in the past 2 decades and we may have forgotten the scourge of purebred catteries this horrible disease once was and could still be again. Although FeLV is most often seen in cats that go outside, it does still strike indoor only cats and spreads aggressively in cattery situations.


FeLV is spread by passage of blood, saliva, and tears between cats in close contact. The principle route of infection is prolonged contact with infected saliva and nasal secretions. Biting also commonly transmits the disease but is not required. Transmission through the placenta and by milk, along with maternal grooming of kittens, results in 100% transmission from queen to kittens. The virus does not survive in the environment so aerosol and surface transmission is not of concern. FeLV has been detected in semen and vaginal epithelium so venereal transmission is possible.

The onset of symptoms after infection could be as early as a few months and most cats (80%) will die with in 3 years. But some will live for 8-10 years before showing symptoms and they are contagious in the meantime. And then there are those latent carriers: cats that test negative but sequester the virus in their bone marrow or other tissues where it can’t be detected with routine testing. These cats are ticking time bombs as their virus can become activated and contagious at any time.

Testing For FeLV

There are 2 types of routine screening FeLV tests:

ELISA (e.g. Idexx Snap):

  • used as an initial screen
  • detects p27Antigen in whole blood, plasma, serum, saliva or tears (plasma and serum give the most accurate results)
  • can get false negatives if you test earlier than 2 weeks after exposure
  • can get temporary false positives if cat has viremia that is self-limiting (i.e. a naturally resistant or vaccinated cat that was recently exposed.)
  • can be inaccurate if poor testing techniques are used.

IFA (immunofluorescent antibody)

  • used for confirming positives
  • only accurate after the bone marrow has been invaded and infected neutrophils and platelets are released, therefore best done at least 4-6 weeks post infection.
  • Positive results are 98% accurate.

Although PCR testing for provirus DNA is done at some universities, there are no routine tests to detect latent carriers.

Routine FeLV screening recommendations:

  • ELISA test at least 2 weeks after last possible exposure.
  • If negative, repeat test at least 8 weeks later to confirm
  • If positive, do IFA test
  • If ELISA positive and IFA negative, repeat IFA in 4-6 weeks.

Final Thoughts

As we observe our immunologically naïve cats lying in a multi-cat heap on the couch, ecstatically slurping on each other’s faces, we must be forever aware of how devastatingly ideal this type of environment is for the spread of FeLV. Please take steps to prevent any resurgence of FeLV and the horrors of past decades .

DO NOT assume that because your cats don’t go outside or that because you only work with close friends that you are not vulnerable. If you swap kittens, if you send your girls out for breeding or allow your precious male to be used for an outside breeding, you could be putting your entire cattery at risk. Test your cats – especially any new cats or kittens that you bring in. One undetected positive cat could destroy your entire cattery.

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