Mad Dogs and Friendly Foxes
I thought I would spend some time over the next several articles discussing viruses and the vaccines we use to protect your pet against them. Viruses are small (very small); not much more than some DNA or RNA wrapped in a protein shell. A virus causes infection by gaining access to cells, then using the cell's energy to manufacture more copies of itself. This ingenious method of reproduction allows viruses to basically party inside the cells, away from most of the body's defenses.
The first virus I'd like to discuss is the notorious rabies virus. If you have dogs or cats, then you've probably taken your pet to the vet for a vaccination against this virus. Rabies vaccine is probably the most comon vaccination in veterinary medicine. It is the only vaccination required by law: the state of New Mexico requires a rabies vaccination every three years for dogs and cats. There are some areas of the world where rabies has never occurred. These areas (mostly islands), are careful not to allow the virus in, hence the long quarantine requirements for places such as Hawaii.
The rabies virus has been around for a long time. The disease was well known long before we discovered the virus. "Mad dogs and friendly foxes" is an old expression used to describe the behavioral changes seen in animals infected with rabies virus. As a veterinary student I was completely fascinated by this clever little virus. Now maybe I just needed to get out more, but I think you, too, may gain a certain respect for rabies after you know a little about it.
Rabies is transmitted from the saliva of an infected animal to a new host, usuallly through a bite. The virus then travels along nerve fibers, eventually landing in the brain. It is in the brain that all the trouble begins. The virus begins to replicate. One potential problem with viruses which kill their host, as rabies does, is that once the host dies so does the virus. Therefore the virus needs some way to transport itself to a new host. Rabies virus accomplishes this by basically making its host crazy. (Isn't this great?) The virus attacks specific regions of the brain, so that friendly and domesticated dogs and cats become vicious crazed animals seeking out new victims to bite. By this time the virus has also moved into the salivary glands. A bite from the infected animal injects thousands of new viruses into the new host. And the cycle repeats itself.
Dr. T. Murt Byrne