The first step in the rescue operation was getting the kittens inside. I repurposed the crate of one of my dogs and quarantined the kittens in my bathroom. Then I made an appointment with the local veterinarian to have all of the kittens checked. If all went well, they were to be vaccinated.
Unfortunately, all did not go well.
The kittens, approximately 7 weeks old, tested positive for Feline Leukemia Virus, or FeLV. This illness is contagious to other cats, is incurable, and is very serious. Kittens who contract the virus this young have a generally poor prognosis in terms of lifespan.
The vet postponed the vaccinations and recommended retesting 4 weeks later. I immediately called my regular vet and was told that there is a possibility that due to their age the test may have produced a false positive, mistaking antibodies from their mother for infection. There is also a possibility that they were infected but can throw off the virus and test negative later both for active infection and shedding the virus, but the window for that to happen is approximately 90 days from exposure.
Some info on the tests used to determine FeLV status:
The ELISA can detect the first stage of infection - the primary, or transient, viremia stage, before bone marrow is infected. At this stage, the cat's immune system may still ward off the virus. So a cat may have been infected and test positive on the ELISA, but still be in this first stage and be able to throw off the virus. Once it has thrown it off, it will test negative. This usually happens within 8 weeks of exposure, but may take up to 90 days. The ELISA test can also detect the virus when it has passed the first stage and entered the second stage, or persistent viremia stage. At this stage the virus invades the bone marrow and normally isn't going to go away.
The ELISA is almost 100% reliable on negative results - i.e. if a cat tests negative on an ELISA test, you can rely on it being negative (one of my vets explained that it is almost impossible for an operator to mess up a negative result) UNLESS you are testing within 90 days of exposure.It can take up to that long for the virus to be circulating in the blood and show up on ANY test. This is why you should never rely on just one test - you may be missing a positive if you do. If, after at least 90 days with no intermediate exposure the cat then tests negative again on an ELISA, it can be assumed to be negative.
The IFA test must be sent to a diagnostic lab, whereas the ELISA is normally done in the vet's office. The IFA detects circulating virus primarily during the second stage (persistent viremia) - in other words, after the "point of no return," which is why if the cat is positive on both the ELISA and the IFA one should treat it as positive and accept that it probably will not revert to negative, and in all likelihood will remain positive for life.
If the IFA test is negative, the cat may still be in the first stage (transient viremia) and still be fighting the virus off, and occasionally you get "discrepant" results: e.g. negative ELISA, positive IFA. With these you need to follow the AAFP's guidelines for retesting. Some may progress to persistent viremia; some test negative but later develop lymphoma later.
So the kittens are going to be retested in two weeks and I plan to have the vet administer two tests, the in-house test that he originally performed (the ELISA) and the one that needs to be sent out to a lab (the IFA). If they test positive on the IFA, then they should be considered FeLV+ for sure and I will adapt accordingly. If they test negative on the IFA but positive on the ELISA, then they may still be able to shed the virus and will need to be retested at the 90 day mark--if they test negative on both tests at that point, then they can be considered negative. If they test negative on both, they will still need to be retested at 90 days but if that test is also negative for both, they can be considered negative.
Or so sayeth my research to this point, after consulting with two allopathic veterinarians, one homeopathic veterinarian, and various rescue and support groups. I apologize if any my logic or conclusions are flawed and NOTHING HERE SHOULD BE TAKEN IN LIEU OF PROFESSIONAL ADVICE. I make no warranty as to the accuracy of the statements or conclusions above. DISCLAIM DISCLAIM DISCLAIM.
The kittens have been returned to quarantine in the meantime.