If an unvaccinated person is exposed to rabies, the protocol is very clear: the person receives a single dose of anti-rabies antibody and a series of four rabies vaccines over a few weeks.
If an unvaccinated dog is exposed to rabies, the typical requirement is a strict six-month quarantine (with rabies vaccination one month into quarantine or one month before the end of quarantine) or prompt euthanasia.
Why? There has been only limited investigation of rabies post-exposure treatments in dogs. Ineffective post-exposure treatment could put the people around an exposed dog at risk of rabies exposure themselves. In the absence of convincing evidence, public health concerns trump animal issues.
A recent study published in the Journal of the American Veterinary Medical Association (Wilson et al 2010) sheds some more light on the topic. The authors reviewed records from rabies-exposed animals in Texas from 2000-2009, where a different post-exposure protocol is used for animals. In Texas, exposed unvaccinated animals are either:
- immediately euthanized, OR
- immediately vaccinated, kept in strict isolation for 90 days and given rabies vaccine boosters during the 3rd and 8th week of quarantine.
The authors reviewed the records of 1014 animals (769 dogs, 126 cats, 72 horses, 39 cattle, 3 sheep, 4 goats and 1 llama) that were treated with this modified protocol after exposure to another animal that was confirmed to be rabid.
None of the treated animals developed rabies.
An important issue to bear in mind is whether the animals in the report were actually exposed to the rabies virus itself, not just a rabid animal. There’s no way to prove that any were actually exposed to the virus, however 29% had what was considered "direct exposure," and a further 38% had "probable exposure." Presumably, not all the animals were actually exposed, but even so, because they looked at so many animals, it provides more convincing evidence that the protocol is effective for preventing rabies. The only definitive way to figure it out would be to experimentally infect animals with rabies and then see if the post-exposure treatment prevents them from developing disease, something that is unlikely to be done for many reasons.
Immediate vaccination may be a key component of this protocol. Previous reports of post-exposure treatment failure have been cases where there was a relatively long interval (e.g. a couple of weeks) from rabies exposure to first vaccination. By that time, it’s possible that the infection is too advanced, particularly since the typical incubation period for rabies in dogs is 21-60 days.
The Texas post-exposure protocol makes sense. It appears to be effective and requires a shorter quarantine period. Those are both important factors, and make post-exposure treatment a more viable option.
However, while this study provides evidence that this protocol may be effective, it doesn’t mean everyone can just start using it. Regional laws regarding rabies exposure supercede these results, and unless the rules are changed, this approach may not be an option. Hopefully, regulatory officials will look at the results of this study and Texas’ experience, and think about modifying their own protocols.
At the end of the day, however, it’s still much better to have your animal properly vaccinated against rabies so that post-exposure treatment or quarantine isn’t needed. Vaccination isn’t 100% effective, but it’s very good overall, and the mandated response to exposure of a vaccinated animal is much easier (on both the animal and owner) than for an unvaccinated animal.