Rabies is an acute and highly fatal viral infectious disease affecting the central nervous system. It is the only communicable disease of man which is nearly 100 percent fatal. Once the animal gets infected with the disease, he rarely lives more than 10 days.
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The term rabies is derived from a Latin word ‘rabidus’ meaning mad. Rabies is also known as hydrophobia because the patient shows fear from water and is unable to drink water in spite of intense thirst.
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It is a disease of warm blooded animals like dogs, cats, monkeys, foxes, jackals and wolves. Amongst domestic animals, dog is the commonest source of infection to man. The other domestic animals like cow, horse and camel etc. can be infected when bitten by a rabid dog and hence these animals can transmit the disease to man on biting.
Causative Organism:
The causative organism of rabies is lyssa virus type 1 which belongs to the rhabdovirus group. It is bullet shaped RNA virus. It multiplies in the nerve cells and is found in saliva, urine, lymph, blood and milk of infected animals.
Mode of Spread:
Rabies is mainly spread by bites of rabid animals (dog is the common example). It may also spread by clicking on a scratched or abraded skin or mucous of a rabid animal.
Saliva of rabid animals is the most common source of infection. The rabid dog dies in about 10 days time and its saliva is infective for first four days. That is why in case of dog bite, the dog in question is watched at least for a period of 10 days.
Incubation Period:
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Incubation period varies to a great extent. In man it ranges from 10 days to 8 months or even longer which depends on the site, number of bites and severity of the bites by the rabid animal. For upper limbs and trunk it is 40 days, while for lower limbs it is 60 days. It is shorter in children.
Clinical Features:
The disease begins with headache, slight fever, pain at the site of wound, saliva runs from the mouth. It stimulates all parts of central nervous system, sensory, motor as well as sympathetic nerves.
The patient cannot tolerate noise and bright light. There is difficulty in swallowing, fear of water and intense spasms on being offered food or fluids. The patient dies due to respiratory paralysis or during convulsions. Once the disease sets in, it is fatal and there is no treatment of hydrophobia. So its death rate is 100 percent.
Signs and Symptoms in Dogs:
When the dog becomes rabid he attacks and bites without provocation, bites unusual objects such as sticks, straw etc.; runs away from home and wanders aimlessly biting anything that comes in its way. There is change in voice and dog barks in a hoarse voice, saliva runs from mouth in large quantities. The animal dies within 10 days of developing the signs and symptoms.
Prevention and Control:
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(i) Clean the wound and scratches with soap and water as early as possible. Then apply spirit or tincture of iodine on the wound and cover it with surgical dressings.
(ii) Observe the biting animal for 10 days, it should not be killed but kept under observation for 10 days. If the animal dies or shows signs of illness within 10 days it means the animal is rabid and antirabies treatment should be started immediately but if the animal survives and shows no signs of illness at the end of 10 days after the bite then the risk of disease is reduced to nil and no antirabies treatment is required except cleaning and dressing of wounds. But antirabies treatment should be given in the following cases:
(a) When the animal dies or shows signs of rabies within 10 days after the bite.
(b) When the biting animal has run away and cannot be traced or identified.
(c) When the bite is from wild animal.
(iii) All stray dogs should be killed and pet dogs should be compulsorily vaccinated.
Antirabies Treatment:
The traditional vaccine is the Semple vaccine which is prepared from brain tissue of infected animals. At Kasauli this vaccine is prepared from sheep brain. Vaccine is given subcutaneously in the anterior abdominal wall in a dose ranging from 2 to 5 ml daily for 14 days depending on the severity of the bite.
Now day’s cell culture vaccines known as Human Diploid Cell or HDC vaccine have been marketed. It is safe and effective vaccine as compared to Semple vaccine but it is very expensive. This vaccine is given in five doses of 1 ml each by subcutaneous or intramuscular injection (never given at the buttock) at 0, 3, 7, 14 and 30 days and a booster dose is given on 90th day