Rabies is a viral disease that is spread most often from the bite of a rabid animal to another animal or to a human.
The rabies virus affects the central nervous system including the brain and spinal cord of humans and animals. During the incubation period, the time between exposure to the virus and the appearance of symptoms, the virus travels along nerves towards the brain. This process takes an average of one to three months, but can range from several days to several years after exposure. The infection causes inflammation of the brain and spinal cord that can lead to encephalopathy and later, death. Encephalopathy is any type of disease that changes the brain's function or structure.
The rabies virus has two forms that cause different behaviors in affected animals. The forms of the disease are called furious and paralytic (dumb). If an animal has the furious form of rabies, it is easily provoked, distressed, and aggressive. Some wild animals may do things that are uncharacteristic for their species when infected with the furious form of the virus. For example, bats may come out during the day, or a wild animal may be friendlier than normal towards humans. With the paralytic form of rabies, some or all of the animal's body is paralyzed.
The bite of a rabid animal is the most common cause of rabies. The virus is carried in the saliva of the rabid animal and is able to enter the body through an opening in the skin, such as a bite wound. Although it is possible to get rabies from a non-bite exposure, this is very rare. For example, non-bite exposures include inhalation of aerosol particles of the virus, or by a rabid animal licking a person's eyes, nose, mouth, or broken skin.
High-risk animals include:
non-domesticated (wild) dogs
Domestic animals like cats, dogs, and cattle can become rabid if bitten, so it is important to vaccinate them against rabies. Recently, steps have been taken in some countries to immunize wildlife populations using oral baits containing vaccines. This is dramatically reducing the spread to domestic populations of animals.
Symptoms and Complications
From the point where the rabies virus entered the body, the virus moves towards the brain along the nerves. A person may show the first signs of rabies an average of one to three months after the virus enters the body. In humans, the first symptoms of the disease are non-specific and resemble other viral infections, they include:
pain at the bite site
a general feeling of illness
poor appetite, nausea, and vomiting
In 4 - 10 days, neurological symptoms will appear as the virus begins to multiply in the spinal cord or brain. These symptoms include:
excessive saliva production
high level of excitement
paralysis of lower legs
problems swallowing due to painful throat and voice box spasms
hydrophobia (fear at the sight of water despite an intense thirst)
Spasms affecting the muscles in the throat and pain or difficulty swallowing are often seen as the disease progresses. Eventually, a person infected with the rabies virus can slip into a coma and die. Death is usually caused by breathing failure. It is important to seek treatment as soon as possible after the initial contact with the infected animal. Treatment must be started before the symptoms develop or it is highly unlikely to be effective in preventing death from the virus.
Making the Diagnosis
Tests are performed on the animal that bit a person in order to confirm the presence of rabies in the animal.This requires killing the animal, if possible. This step is necessary because a person will not immediately show antibodies to the virus after being in contact with a rabid animal.
If the bite came from a pet that appears sick, the pet is euthanized so its brain can be tested for rabies. However, pets that do not show signs of the disease but are suspected of having had contact with a rabid animal may be quarantined and observed by a veterinarian over a certain period of time.
Treatment and Prevention
People should seek immediate treatment by a doctor after a bite or contact with an infected animal. The sooner treatment is started, the more likely a person will avoid developing the disease. Once symptoms appear, the rabies vaccine and immunoglobulin are not effective and death is almost certain. Rabies is a disease that must be reported to the authorities by law in Canada.
The most common treatment of rabies is with post exposure prophylaxis. The first step in treating rabies and to reduce the likelihood of developing symptoms is to wash the wound with soap and water.
The next critical step to prevent rabies includes a dose of immunoglobulin against the rabies virus followed by a strict schedule of injections of the rabies vaccine. The immunoglobulin provides immediate protection against the virus to "bridge the gap" until the vaccine starts working. The vaccine helps the person's immune system produce antibodies against the potentially lethal virus. The vaccine protects individuals for approximately 2 years.
People such as veterinarians or cattle farmers who work with potentially infected animals or humans need to be vaccinated against rabies. They will also have periodic blood tests to see whether they need booster shots of the rabies vaccine.
You can prevent being infected with the rabies virus by remembering these tips:
do not feed wild animals and stay at a safe distance when observing them
supervise children and teach them not to approach or touch animals they do not know
stay away from animals showing signs of rabies
do not bring home wild animals
if you suspect an animal is rabid, stay away from it and contact the local authorities
if you have pets or livestock, make sure to vaccinate them against rabies