Hi,
I'm so sorry to hear your kitty has leukemia! I understand completely why you are so upset. The way this happened when your kitty has been vaccinated is that the vaccine is 70% effective. That means that it will work like it should, and protect 70% of the cats given the vaccine. So the reverse is that 30% of cats given the leukemia vaccine will not be protected. Here is a link to the page about this from the company that produces the vaccine:
http://www.pfizerah.com/PAHimages/compliance_pdfs/US_EN_LK_compliance.pdf
Hopefully, your other cats have developed immunity and will be fine. As long as this kitty hasn't been fighting with the other cats the risk is minimal.
If you have further questions let me know. If this answers your question please click accept. Thank you and take care!
Lynn
I'm sorry, I misread your question, and thought the sick kitty was indoor/outdoor. There are a couple possibilities here. While they may seem unlikely, obviously one of them happened. Your indoor/outdoor cat could be a carrier of the virus. He may have tested negative, but have since been exposed to the virus, became a carrier, and brought it in. The virus can be spread through casual contact such as sharing food and water bowls.
Here's the next possibility. If the sick kitty's original negative leukemia test was done when he was quite young it can be a false negative. He may actually have been carrying the disease for years without being sick. We've actually had this happen a couple times at the veterinary clinic I work at. The cats were tested (negatively) as kittens, received vaccinations, kept indoors, and years later showed up sick and tested positive for leukemia.
I can see why you aren't clear, because it is very confusing. But the fact remains that your sick cat has developed leukemia. False negative tests CAN occur at any age, they are more likely in young kittens, but not impossible in older cats. What happens is that sometimes cats that are positive don't have high enough levels to register positive on the test, so they show up as a negative. Then later on the numbers increase. So, yes, your outdoor/indoor cat could technically be a carrier. Or the sick kitty could still have been harboring the disease all these years. False positives are also possible so if you want to re-test the sick kitty you could request it. There are two types of test for the disease so to confirm it you would need to do whichever one wasn't used the first time. Here is a link to a page about leukemia that explains some of this more down towards the bottom of the page:
http://www.peteducation.com/article.cfm?c=1+1316&aid=211
Yes, its a good idea to be certain because his symptoms could be caused by the other two problems he has right now as well. If it does come back positive then you may want to consider testing your cats a second time.
Yes, it wouldn't be a bad idea, though I realize the cost may be prohibitive.
Yes, they can - you have one cat that did exactly this if his 2nd test comes back positive. Normally, this isn't something that has to be done periodically, but because you have one cat that is positive it makes the risk to the other cats much higher.
Veterinary Assistant
worked at a vet clinic for 15 yrs, BA in biology, have had cats most of my life
You're welcome!