Rabies

What is Rabies?

Rabies is an acute viral disease of the central nervous system that affects all mammals. It is transmitted by infected secretions usually saliva. Most exposures to rabies are through the bite of an infected animal.

Rabies exists in two forms.

1. Urban: Propagated chiefly by unimmunised domestic dogs and cats.
2. Sylvatic: Propagated by jackals, foxes, wolves and bats.

Infection in domestic animals is by exposure to the sylvatic reservoir of infections. Human beings can be infected by either urban or sylvatic reservoirs. Dogs are an important vector of the rabies virus for humans.

The first event is the introduction of the live viruses through the skin or mucous membrane. Initial
virus multiplication occurs within the muscle cells at the site of the bite. The nerves get affected thereafter. The virus then spreads up the nerve to the central nervous system. Once the virus reaches its destination it replicates almost exclusively within and then passes along autonomic nerves to reach other tissues-the salivary glands, the adrenals, kidney, lung, liver, muscle, skin and heart. Passage into the salivary glands facilitates further transmission of the disease via infected saliva.

The incubation period is variable from 10 days to over one year (mean 1-2 months). The time period appears to depend upon the amount of virus introduced, the amount of tissue involved, host defense mechanism and the actual distance that the virus has to travel from the site of inoculation to the central nervous system.

The classical pathological lesion of rabies is the Negri body. It is made up of fine matrix and rabies virus particles. Negri bodies are distributed throughout the brain.

Clinical Features of Rabies

1. Prodromal Period:

Persists for 1-4 days marked by fever, headache, malaise, body ache, fatigue, anorexia, nausea, vomiting, sore throat and a cough. There may be complaints of tingling and numbness, fasciculation of muscles.

2. The Brain Infection:

This begins shortly after the virus reaches the central nervous system. There is excessive muscle activity, restlessness, excitation, agitation, confusion, hallucinations, combativeness, bizarre thoughts, muscle spasms, posturing, seizures and focal paralysis. Mental aberrations alternate with complete lucid periods. As the disease progresses, the lucid periods shorten until the patient lapses into a coma.

There is excessive sensitivity to bright light, loud noise, touch, and gentle breeze. The temperature may be high (40-41 degrees C).

The patient has dilated irregular pupils, increased lacrimation, salivation, perspiration, hypertension. Muscle paralysis takes place. Paralysis of the vocal cord takes place.

3. Brainstem Dysfunction:

Cranial nerve paralysis resulting in double vision, facial paralysis, optic nerve inflammation and difficulty in swallowing. The combination of excessive salivation and difficulty in swallowing produces the traditional picture of foaming at the mouth. Hydrophobia, the painful violent involuntary contraction of the muscles of respiration, pharyngeal and laryngeal muscles initiated by swallowing liquids is now present. With coma, there is the failure of the respiratory centre and death.

Survival after the onset of symptoms is 4 days with a maximum of 20 days in the best Facilities. Recovery is very rare.

Management:

Emergency evacuation to a hospital.

Prevention:

Active immunization with Human Diploid Cell Vaccine.