Rabies from ancient times was regarded as the ‘mad dog disease’. It is being transmitted to human from the bite of mad dogs. Traditionally, the dogs are believed to be prone to a condition of madness during the summer season. The disease once in humans is termed as ‘hydrophobia’ as the patient develops a fear of water. It is due to the incapability to drink water and inability to tolerate the excessive thirst that is felt by the patient.
Initially, it was believed that the saliva of dogs caused rabies, but only after Pasteur established the presence of a virus in the brain of rabid dogs, the correct causative agent was identified.

Pathogenesis
When rabid dogs bite humans, the virus present in the saliva enters the body through the wound. The virus multiplies in the nerves and tissues at the site of deposition of virus for 48-72 hours.

It pierces through the nerve endings to reach the spinal cord and brain. Once inside the brain, it again undergoes further multiplication and disseminates to almost all parts of the body including the salivary glands.

There it multiplies further and leads to the shedding through saliva. It is even present in the cornea and facial tissues of the patient. The virus is also shed through urine and milk. Incubation period in humans is 1-3 months. It lengthens if the bite is on the legs and shortens if the bite is on the face or head.

The diseased condition starts with fever, headache, restlessness, fatigue and sleeplessness. Site of entry of the virus becomes painful and fasciculate.

The course of the disease is grouped into 4 stages;
1. Prodrome; Prodromal phase is characterized by anxiety, agitation, irritability, depression, insomnia and nervousness.
2. Acute encephalitic stage; this phase starts with hyperactivity in response to external stimuli. The person shows bizarre behavior, agitations, etc. The patient develops intense thirst, but is unable to drink water.
Solid foods can be swallowed. Pharyngeal and laryngeal spasms are created when attempts are made to drink water, thus leading to fright to water. Tremors become common.
3. Coma; those patients survived from acute phase moves on to the coma stage.
4. Death; within 1-6 days respiratory arrest occurs during tremors leading to death of the person. Paralysis follows in certain cases.

In some of the victims, a psychological disorder develops namely hydrophobiophobia. They express anxiety, irritability and exaggerated hydrophobia. They are generally sedated and referred to reassurance treatment.

Histopathological effects occur in the brain like blocking of blood flow, accumulation of fluid in the cerebrum and the edges of the blood vessels become permeable.

In dogs, two kinds of rabies seem to appear. Rabid dogs usually die in 3-5 days.
1. Furious – more common type, dogs runs continuously, bites without provocation. It progresses to sagging of the lower jaw, salivating constantly from the mouth, followed by paralysis and death.
2. Dumb – paralytic form, the animal becomes huddled, unable to feed, deficient feeding.

Rabies is also found in cats, cattle, horses, jackals and other wild animals.

Diagnosis of rabies is mainly by;
1. The detection of inclusion bodies in the cytoplasm (Negri Bodies). It contains a fibrous matrix with the virus particle
2. Immunoflourescence for detection of viral antigens
3. Isolation of virus from tissue culture cell lines
4. Reverse transcription PCR to detect the viral RNA