Pneumabort-K Vaccine Reaction
Qustion: “I have administered the Pneumabort-K vaccine three times to my mare. The last two doses caused her to walk as though she is stiff or could not feel her lower legs. Have you ever heard of this? Do you think it will cause her to abort?”
Obviously, without being able to evaluate the mare or knowing a thorough history, I cannot definitively say anything about your mare’s condition. What caused her stiffness, etc. So take what I do write with a grain of salt. I would encourage you to seek advice and consultation from your veterinarian.
First, the stiffness and lower leg issues sound like a vaccine reaction to me. It is relatively common for horses to react in this way after being given any number of different vaccines — including the Pneumabort-K vaccine. These vaccine reactions are typically not serious and pass of themselves in a couple days with limited or no treatment.
As to whether these vaccine reactions will cause your mare to abort, the short answer is no, at least not directly. But your question and your description of your mare’s reaction to the Pneumabort-K vaccine does bring up an interesting discussion — as to whether these vaccine reactions can cause reappearance of EHV-1 in mares who are latently infected, and consequently abortion.
As you probably know, many horses are latent carriers of EHV-1. Latent carriers show no obvious effects of the virus, though they are infected and can show symptoms and spread the disease if the virus wakes from latency. This reappearance of the virus can be brought about by stress (e.g. stress induced by transport, showing, sickness due to various disease states, etc.) Horses that are carriers of EHV-1 do not produce the same immunoresponse to the Pneumabort vaccine — as previously unexposed horses. Because of this reduced or inadequate immune response, the vaccine offers them little or no additional protection against the virus. BUT, the horses still have the stress of the vaccination and of a possible vaccine reaction. This stress may be enough to cause the latent, non-vaccine strain of EHV-1 to reappear — and cause abortion in the mare. The Pneumabort-K vaccine itself does not cause abortion, but the vaccination of the mare sets off a course of events leading to abortion.
The obvious question this scenario raises is, “Is my mare a latent carrier of EHV-1?” Unfortunately, there is no way to know. No test exists to identify carriers of EHV-1. And even if there were, there is no way to predict when and if the latent virus will revert to virulence.
I want to be clear: I am not saying that this mare is experiencing the above scenario. What’s more, the above scenario is conjecture and has no data behind it. DO NOT mistake what I’ve written for fact. The question raises this interesting area of discussion surrounding the Pneumabort vaccine. But this discussion, this conjecture does not change the fact that the standard of care in veterinary medicine is to vaccinate mares with the Pneumabort vaccine at 5, 7 and 9 months.