A Study of Immunity to Rabies After Expired Vaccines
We are lucky in the U.S. that rabies among our domestic animal companions is rare, though not unknown. This is because rabies is considered a public health risk and it’s law in most states that cats and dogs must be vaccinated against it. It’s rare that the disease is passed along from another domestic pet or animal exposed to and infected with rabies, rather the infection usually comes from wildlife, most often raccoons who share our world even if we aren’t aware.
It’s only February and the temperature was five degrees Fahrenheit when a few nights ago I saw all my cats staring out the front windows and door into the darkness, the motion-sensor porch light flicked on to reveal a large raccoon bumbling around on the front porch. I would not expect to see a raccoon this early, especially since our temperatures have not been above freezing for at least a month, but there he was, and any animal outdoors could encounter him. I noted the raccoon because it was out of the ordinary, just as I had noted one I’d seen in my yard in daylight one autumn morning. It may be they are waking up this early, but it’s odd enough behavior that it might also be ill.
And aside from raccoons, one of the cats in the study mentioned below was bitten by a bat, a common vector species for rabies. One of the cautions given to humans in exposure to rabies is to take note of any bat you see inside your home because you may not notice a bite from one, especially if you were sleeping when it happened.
It’s also characteristic of rabies that infected animals tend to act erratically and appear when and where they aren’t expected, so planning ahead and trying to protect your pet from exposure isn’t really a good plan.
Owners must keep proof of a current vaccine in the case their pet bites another animal or a human, and that proof is also essential when the pet is bitten by an animal that may be rabid. Rabies can take quite some time to develop and pets are generally quarantined, but pets who have a current vaccine are quarantined in a much less restrictive way than one which has an expired vaccine, or one that has had no vaccine at all according to guidelines in the “Compendium of Animal Rabies Prevention and Control“.
The Compendium requires pets with a current vaccine be given a booster at the time of the incident and be observed for 45 days but not quarantined or restricted; some areas may go beyond the requirement and require it by local law.
The requirement for pets with no vaccine is pretty dire—euthanasia or quarantine for six months in a specialized facility paid for by the owner.
Pets with expired vaccines are often treated as if they have had no vaccine at all because the presence of antibodies carried beyond the stated duration of immunity from the vaccine hasn’t really been tested to any great extent, including taking into account how long it’s been expired. Titer testing often finds an acceptable level of immunity in a pet with a vaccine that’s been expired for even a period of years.
And in addition to the level of antibodies found in everyday testing with no exposure to rabies is a test of “anamnestic” response. When the body builds up an immunity through exposure to the illness, it keeps a certain level of antibodies floating around for immediate use, but when exposed to the actual antigen the body “remembers” having encountered this foreign body before and the immune system immediately begins building up the defense it had manufactured when it either had the disease earlier or was vaccinated for it. This would mean that, even though a vaccine is expired there is not only residual immunity, but the body can mount a full response to it as if the vaccine was current.
That’s a difference of life and death for a pet whose vaccines are not current, or for which a current record can’t be produced. A small study of dogs and cats who were exposed to rabies showed that indeed an expired vaccination–even up to 46.1 months expired—still provided the animals with an acceptable level of immunity, and with a booster at the time of exposure they had full immunity in days. Best of all they did not have to spend six months in quarantine or die to avoid the risk of their having contracted the infection, but could be observed much as their fully-vaccinated counterparts.
I am thinking also of our community cats who receive a rabies vaccine along with spay or neuter in TNR clinics. Trapping and vaccinating them all each year is nearly impossible, but this study proves that they likely have enough residual immunity even without annual vaccines, at least for a few years.
Resources
Read the full study with all statistics, results and charts in Journal of the American Veterinary Medical Association, January 15, 2015, Vol. 246, No. 2, Pages 205-211: Comparison of anamnestic responses to rabies vaccination in dogs and cats with current and out-of-date vaccination status.
Also, the article about the study on the Winn Feline Foundation website may be a little easier to follow: Immune response to rabies vaccination.
Also of interest, read the full text of the “Compendium of Animal Rabies Prevention and Control” in Journal of the American Veterinary Medical Association, September 1, 2011, Vol. 239, No. 5, Pages 609-617.
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NOTE: The cat at the top (and below) does not have rabies. She is Carly who I met last May at one of the TNR clinics last year, then transported her to a temporary foster on the way to her forever home. Carly came from a pretty rough part of town and had been hit by a car but was rescued and brought to the clinic. One hind leg was removed, and she also tested FeLV+, but was nonetheless leaping around her cage and poking her arms out trying to get attention, after all her traumas still enthusiastically friendly. She actually went to a forever home with one doting human and no other kitties, but we suddenly lost her just recently to the effects of FeLV. We won’t forget you, Carly.
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Godspeed Carly…you are, and always will be a beautiful girl
we are happy that you DID find your forevers, our sincerest sympathies to your mom/dad ♥♥♥♥♥
loves from boomer, dai$y, tuna ~~~~ & dude & sauce too.
Carly is probably running with the guys up there, with all four legs and purrfectly healthy!