Zoonosis Week: Rabies

Zoonosis: An infectious disease in animals that can be transmitted to people. The natural reservoir for the infectious agent is a animal.

I'm starting to realize that I'm on an "R" pattern with these diseases. Don't worry, it won't stay that way.

Rabies is one of the "big baddies" of zoonotic diseases. In fact, it's such a concern that in the US and many other countries, animals are required by law to be vaccinated for it. This disease is treated so seriously because there really is no treatment once symptoms are evident, and it is almost always fatal. So let's learn a little more about it.

Rabies is a virus transmitted through saliva. The virus replicates in the salivary glands of an animal with advanced disease, and can then become infective through either a bite or through contact with mucous membranes (mouth, nasal passages, etc.) and broken skin. Most people think of the infection through being bitten by an infected animal, but this is not the only way. There have been many stories in vet school of veterinary students and faculty examining a horse or cow with excessive salivation, even sticking their hands in its mouth, and then having to be treated for rabies exposure. If the person had a cut or other wound on their hand, the saliva could get into the body through that injury. Rabies cases have also been documented in people who have gone into caves with numerous rabid bats, inhaling the aerosolized saliva and becoming infected through the membranes in their lungs.

Once through the skin the virus will eventually migrate to the peripheral nerves. How long this can take is variable, and is not really predictable. Once it reaches the nerves, it quickly spreads to the brain where it causes encephalitis and eventually death.

Symptoms can vary, but are almost always neurological. This can include confusion, behavior changes, paralysis, uncoordinated movements, and seizures. In fact, we are taught in vet school to include rabies as a possibility in any case that shows neurological signs. Symptoms usually begin within a few weeks of exposure, but can take as many as a few years.

Prevention is a matter of vaccination and avoidance. Since any mammal can potentially become infected with rabies, mass vaccination of wild animals is impossible. There have been programs where bait is laced with an oral vaccination in hopes of reducing the cases, but these many not have wide-spread efficacy. Vaccinating pets and livestock is the best way of avoiding transmission of the disease through animals commonly in contact with humans. There is also a vaccine for humans that many of us veterinary staff receive since we are at highest risk. Other than vaccination, the average person should avoid direct contact with wild animals, especially ones showing odd behaviors.

If someone becomes exposed to the disease, receiving post-exposure injections can prevent the disease from spreading. This has to be done quickly, as the end is pretty much a foregone conclusion once the virus reaches the nerves. This speed of spread is why treatment is often started when exposure is suspected but not yet confirmed.

Here are a few other tidbits for you...
* Rabies kills around 55,000 people each year world-wide, mainly in Africa and Asia.
* There are only six known cases of people surviving rabies once symptoms began.
* Louis Pasteur and Emil Roux developed the first rabies vaccine in 1885.
* It is also sometimes called "hydrophobia" because of the victim's inability to swallow water.
* In the Stephen King novel, Cujo is a rabid dog.
* Old Yeller (from the movie of the same name) had to be killed because he contracted rabies.
* Infected bats, monkeys, raccoons, foxes, skunks, cattle, wolves, dogs, mongoose, or cats provide the greatest risk to humans.