The rabies virus affects dogs and all other warm-blooded animals. In wildlife animals, rabies is commonly seen in foxes, skunks, raccoons and bats. Each of these species carries a variant strain of the rabies virus. All of these strains can affect animals. Domesticated animals such as cows, horses, dogs and cats commonly act as a source for human infections but people can be infected from wildlife sources as well, particularly bats.
The first step to controlling rabies in dogs an other pets is vaccination. All healthy pets should be vaccinated. The rabies vaccine is very effective, inexpensive, and is usually given every 3 years. In horses, it is usually given every year. In most localities, the law requires rabies vaccinations for all pets.
The second step to rabies control is a thorough understanding of this terrible disease so that risk exposures or contact can be prevented. The third step toward controlling rabies is cooperation between veterinarians, the public, the public health system, and those government agencies who monitor and control rabies on a regional level. For example, in some parts of Canada, bait is dropped from airplanes into rural or countryside areas so that wildlife will eat the bait (disguised as food treats) laced with an effective protective vaccine. Public health departments also track and manage human exposures. Rabies moves to and from animals and people through a bite wound or through breaks in the skin or mucous membranes. It’s thought people can become infected by breathing air around bats, such as in bat caves where the virus is suspended in droplets in the air.
Rabies is almost always fatal. However, if a dog or person is bitten by a rabid animal and begins treatment prior to experiencing symptoms, there is an effective post-exposure treatment, which involves an injection of immune globulin and several rabies vaccines given to the infected victim over a 28-day period.
Once the rabies virus enters the body of the animal or person, it travels to the central nervous system along the nerve fibres. It sets up a base in the brain and spreads back out into the body using the nerves to move around. The virus particles end up in many body tissues. Of particular importance are the salivary glands. Once rabies viruses enter the salivary glands they’re present in large numbers in saliva and are easily spread between animals or people via licking or biting.
Once infected, dogs and other animals may show widely differing symptoms depending on what stage of the infection they are in. Early in the infection they appear completely normal. This pre-symptom phase can last for long periods of time. A bite on the face will tend to lead to a shorter prodromal phase since the virus is close to the brain, while a bite on the tip of the tail or paw may result in a long phase because it takes longer for the virus to travel to and from the brain.
For a few days at the very end of this prodromal or normal-behaviour phase, rabid dogs and animals can pass the virus on to other animals or people. This is the greatest time of risk because the typical rabies behaviours are absent. Once clinical signs of illness start, the animal only has about a week to live. Typically a phase occurs where rabid animals becomes very nasty, and will be irritable and snap and bite without being provoked or bothered. They may attack. This phase is termed furious rabies because the animal seems uncontrollably angry. Finally, the animal becomes progressively paralyzed, termed dumb rabies, and dies because the muscles for control of swallowing and breathing, amongst others, lose their function.
Unfortunately, not all cases follow typical progressive symptoms. For example, rabid cats often become overly friendly and affectionate rather than vicious. They can snuggle up to a child and suddenly lash out with teeth and claws after appearing quiet and nice. A dog may just show what appears to be a paralyzed tongue hanging out. The dog may be quiet, with jaw hanging open and saliva dribbling out of the mouth. One might think he had something like a stick stuck in the roof of his mouth! How about a cow that is restless, foaming at the mouth and when approached, is irritable and grabs a person? Though cows do not have a pile of sharp teeth at the front of their mouth like dogs or cats, this can result in a bite that breaks the skin. How about a pony in a petting facility that gets “nippy” and bites those passing by? Affected animals may also have trouble drinking or eating, and run a fever.
Do these stories sound far fetched? They are all cases veterinarians have seen in practice, so never forget that any animal acting in any unusual fashion can be showing signs of rabies! That is why rabies is called the great pretender. It can look like many other conditions, and can be very different from the vicious biting rabid animal image we hear about.