Rabies -cause, clinical features and prevention

Rabies is an infections disease caused by a virus. The disease which is almost always fatal is usually contracted following bite by an infected animal. The usual culprits are bats, dogs and cats. Rodents can rarely transmit the infection.

Although every bite of an infected animal may not cause the disease an overcautious approach has to be adopted because of the fatal nature of the disease.

The risk depends on the type of animal (bats carry the highest risk), location of the wound (bites on head and neck and upper limbs carry greater risk) and the extent of the wound.

Because the saliva of an infected animal contains the virus even licks on broken skin can cause infection. Scratches by an infected animal are also dangerous because dogs and cats often keep their paws in their months and thus have infective saliva on their paws.

Symptoms and signs: The symptoms usually start between 10 days to 90 days after bite by an infected animal. Rarely the disease can manifest after nearly one year following bite.

Abnormal sensation as the site of the bite is usually the first symptom. Psychological changes appear later in the form of anxiety, irritability or depression.

Later spasm of muscles occurs. Attempt to swallow causes severe spasm of pharyngeal muscles with pain. The patient gets scared merely at the site of water (hence the disease used to be called as hydrophobia which means fear of water).

Eventually convulsions and paralysis of various cranial nerves occur culminating in coma. Patients usually die within 2 weeks of onset of the disease.

Diagnosis can be confirmed by demonstrating the antigen in scrapings of cornea or tissue obtained by skin or brain biopsy. Antibodies can be detected in blood after 1 week. Negri bodies can be seen in the brain cells of some patients but are not considered as specific to this disease.

Treatment: Survival is so rare that rabies can be considered as synonymous with death. Very few have survived with intensive care including drugs to control convulsions, intravenous nutrition and general supportive care for coma.

Prevention: The disease can be prevented by the administration of a vaccine. It is usually given after exposure to the virus through bites or scratches. Those who are at high risk (eg. veterinarians and animal handlers may be given pre-exposure prophylaxis. For more information visit childhood vaccination. Pet animals should be immunized.

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