Strange panleukopenia test results in kittens

Question: 

We have had a few bouts of enteritis which isn't totally unexpected as we deal with 70% ferals. After reading your articles we vaccinated a new lot of kittens at 5-6 weeks.  Four weeks later one got sick and tested positive on a parvo snap test.  He was euthanized.  But the other 2 kittens are fine and have no other signs....

I cannot help thinking this isn't true enteritis.......could the positive snap test be a result of maternal antibodies or vacination? Or is it just a mild case of panleuopkenia?

Answer Date: 
December 13, 2011
Answer: 

If these kittens only received one vaccine at 5-6 weeks there are a few different scenarios that could have happened.  One scenario is that the kitten who got sick still had maternal antibodies at the time of vaccine and thus the vaccine was not able to cause the appropriate immune response to produce protection against panleuk in the kitten.  At some point after the vaccine, the kitten was exposed to the virus and since it was not protected, developed disease from it.  The other kittens in the litter may not have had maternal antibodies at the time of vaccine and thus were able to produce an appropriate immune response.   If they too were also exposed to the virus, they were protected and did not get sick.
 
Alternately, a second scenario is that all of the kittens in the litter had very high levels of maternal antibody at the time of vaccination and the vaccine was not able to penetrate to protect any of them (this would not be uncommon at 5-6 weeks of age). The kitten that got sick could have had the lowest levels and these decreased to the point that he/she got sick when exposed to the virus, while the others still have enough antibodies left to protect them. This is why it is important to bathe kittens immediately if they have been exposed to panleukopenia and place them in a freshly sanitized cage. If this is not done, the exposed kittens may become infected from any virus remaining on their fur or in the environment as maternal antibodies decreased over the subsequent days. Keep in mind that it is possible for kittens that have partial maternal antibody protection to be protected from serious disease but not from infection or shedding.  Because of this it is always best to parvo test the whole litter to make sure there are not any subclinical shedders and always retest if any kittens develop even mild enteritis in the subsequent couple of weeks.

In general, the best protection we can give them is to ensure that ALL cats and kittens receive their modified live FVRCP vaccine on INTAKE - a lag of even a day can leave them unprotected. In most cases robust immunity for panleukopenia from a modified live vaccine develops within about 72 hours in susceptible cats, and likely partial immunity develops earlier.  Note that ALL cats include nursing and pregnant queens and sick animals.  All kittens < 4 months should be given vaccines every 2 weeks starting at 4 weeks of age until 20 weeks.  This can be very cost prohibitive for some shelters. We provide some cost saving ideas in another FAQ entitled  Vaccination protocol in the face of a panleukopenia outbreak.

As for the SNAP tests, it is possible for cats (as well as dogs) to have false-positives on parvo snap tests during a period of roughly 4 to 14 days following vaccination. However, post-vaccination false positives are quite rare, and when they occur, they are usually weak. Strong positive results in combination with consistent symptoms or a high risk history, as appears to be the case with this kitten, are unlikely to be due to vaccination and are a reliable indicator of actual disease. MOST cats (and dogs) will test negative even in the two weeks after vaccination, so even a weak positive in conjunction with a high risk history and/or consistent clinical signs should be viewed with suspicion and the animal carefully isolated.  Also, parvo snap tests are an antigen test and thus maternal antibodies do not influence the result of the test.
 
As you know the common clinical signs are vomiting, diarrhea, dehydration and sudden death/found dead in cage (especially suspicious in adolescent to adult cats with or without concurrent URI). It is possible however for cats to have mild or sub-clinical infection – while we do not usually find these to be clinically important in shelter settings, as noted above it’s something to be especially aware of when dealing with exposed littermates.
For panleukopenia the incubation is usually 5-7 days and there are reports that it has taken as long as 14 days from natural exposure to clinical signs in shelters.  Thus, for any cats that are exposed, quarantine recommendation is 14 days post exposure.  Cats may be contagious 2-3 days BEFORE clinical signs are noted and may continue to shed for 2-3 weeks post recovery (and rarely up to 6 weeks).

 

Some main points that we know for sure about panleukopenia:  major outbreaks rarely occur in facilities that vaccinate all cats with a MLV parenteral vaccine at admission;  a large percentage of cats presenting to shelters are susceptible to panleukopenia; vaccination with MLV vaccine provides almost immediate protection for most cats; environmental contamination and fomite transmission are significant factors for transmission; and bleach and Trifectant are the most effective environmental disinfectants against panleukopenia for use in shelter settings. For more helpful information on panleukopenia please see our Feline: Panleukopenia information sheet and a PetSmart Charity Webinar about Panleukopenia.  Another valuable resource is the textbook Infectious Disease Management in Animal Shelters available at  Amazon and other fine establishments.
 
Cynthia Karsten, DVM
Resident, Koret Shelter Medicine Program
Center for Companion Animal Health
UC Davis School of Veterinary Medicine
www.sheltermedicine.com
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