RABIES: The Great Pretender

Rabies is an uncommon disease in Canada, thanks to the efforts of many concerned people, but veterinarians strongly emphasize the importance of everyone being fully educated about it.

The rabies virus affects all warm-blooded animals. In wildlife, it is most 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 pets, humans or domestic 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 rabies control in pets is vaccination. All healthy pets should be vaccinated. The rabies vaccine is very effective, costs very little, and it 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 high-risk exposures or contact can be prevented.

The third step to controlling of rabies is cooperation between veterinarians, the public, the public health system, and government agencies to 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 between animals or from animals to people through a bite wound or through breaks in the skin or mucous membranes. It is thought that 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 certainly fatal. Recoveries are rarely reported. Once the 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 once more. The virus particles end up in many body tissues. Of particular importance are the salivary glands (the glands that produce saliva). Once rabies viruses enter the salivary glands they are present in large numbers in saliva and can be easily spread between animals or to people via licking or biting.

Once infected, animals may show widely differing symptoms depending on what stage of the infection they are in. Early in the infection (prodromal) 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 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.