Whoever said, ‘barking dogs don’t bite’, has obviously never seen a rabid dog. But those who have, will agree that both the bite and the bark of a dog infected with rabies are viscous. For that matter, it’s the same with any animal infected with the disease. Unfortunately, people usually associate rabies only with dogs. In reality, a bite from any infected animal can cause rabies. Cats, dogs and cattle account for nearly 90 per cent of rabies cases in domestic animals, with horses, mules, sheep, goats and ferrets making up the remaining cases.
According to the World Health Organization [WHO], over 55,000 people die of rabies each year. About 95 per cent of those deaths occur in Asia and Africa and 30 – 60 per cent of the victims are children under the age of 15. Most often, the culprit is an infected dog.
A virus is the villian
Rabies is an acute viral disease, which attacks the brain and central nervous system of its victims. It travels through the nervous system, eventually inflaming the brain. Early symptoms include irritability, headache, fever, and sometimes itching or pain at the site of the bite. The disease eventually progresses to paralysis, spasms of the throat muscles, convulsions, and delirium. Symptoms usually develop between 20 and 60 days after exposure. Without preventive treatment, it is fatal. The good news is that it is fully preventable through vaccination.
Course of the disease
The rabies virus, present in the saliva of an infected animal, is usually spread by a bite or a scratch that punctures the victim’s skin. The virus concentrates in the salivary glands, which explains why it is usually spread by bites. It also invades and damages the muscles involved in drinking and swallowing.
The virus has a strong affinity for cells of the nervous system. It enters nerve cells at the site of the wound, travels to the brain, and then follows other nerve pathways to muscles and organs that are especially affected by rabies.
However, there are other rare ways in which rabies can be contracted. Inhaling the air in places inhabited by rabid rats can directly lead to contraction of the disease. Studies have also revealed that people contracted rabies following implants of corneas from donors who had undiagnosed rabies.
There are generally two types of rabies differentiated by the symptoms observed—Furious and Dumb. In the Furious form of the disease, rabid animals may become aggressive, combative, and highly sensitive to touch and other kinds of stimulation and they can be vicious. This kind is traditionally associated with mad dogs.
In the Dumb form, the animal is lethargic, weak in one or more limbs, and unable to raise its head or make sounds because its throat and neck muscles are paralysed.
In both kinds of animal rabies, death occurs a few days after symptoms appear, usually from respiratory failure.
In humans, the course is similar. After a symptom-free incubation period that ranges from 10 days to a year or longer [the average is 30 – 50 days], the patient complains of malaise, loss of appetite, fatigue, headache and fever. Over half of all patients have pain [sometimes itching] or numbness at the site of exposure. They may complain of insomnia or depression.
About 2 – 10 days later, signs of nervous system damage appear. Hyperactivity and hypersensitivity, disorientation, hallucinations, seizures, and paralysis are some of the prominent symptoms. Death may be sudden, due to cardiac or respiratory arrest, or follow a period of coma that can last for months with the aid of life-support measures.
Most human victims and apparently lower animals as well, suffer excruciating pain on swallowing liquids. Though they suffer from thirst, animal and human rabies victims can be terrified by the sight of water. Hence the disease is also known as hydrophobia.
Unlike other immunisations, the rabies vaccine is administered after exposure to the virus. This unusual technique is successful because the rabies virus takes a comparatively long time to induce disease, a minimum of 10 days, and in rare cases, up to a year.
The length of the incubation period apparently depends on both the location of the wound —the farther from the brain, the longer the incubation—and the dose of virus received.