Rabies: A Life Threatening Disease

Rabies: A Life Threatening Disease

Dr. Rakesh Kumar Khinchi

Sr Assistant Professor

Deptt of Veterinary Medicine, College of Veterinary & Animal Science, Navania, Udaipur

Rabies is a deadly, zoonotic, neurologic disease. It is also known as Hydrophobia in humans and Mad Dog, Lyssa, Tollwut in animals. Lyssa virus (Family- Rhabdoviridae; Order– Mononegavirales), RNA virus, bullet shaped virus and neurotropic in nature. The disease was reported in the works of Aristotle (322 BC). Virus was isolated in 1881 by Roux. The rabies vaccine was developed in 1885 for man. The virus is inactivated by heat (50^OC in 15 min), sunlight, disinfectant (alcohols) and detergents. The different serotypes of rabies virus are:

1. Lagos bat virus
2. Mokola virus
3. Duvenhage virus
4. European bat lyssa virus I (EBL I)
5. European bat lyssa virus II (EBL II)
6. Australian bat lyssa virus

Based on the antigenicity, rabies virus is classified as fixed or street rabies virus.

Reservoir and Host:

Primary reservoirs are foxes, bats, raccoons, skunks, dogs, cats and cattle. All warm-blooded animals including man are susceptible to rabies.

Epidemiology:

In India, Andaman, Nicobar and Lakshadweep islands are free of rabies. Rabies has worldwide distribution. Dogs are the main source of human rabies deaths, contributing up to 99% of all rabies transmissions to humans. The disease occurs in two forms: Urban and Sylvatic. Man is the dead-end host in the infection cycle.

Transmission:

Virus in fresh saliva is transmitted via bite, scratch or abrasion by a rabid animal. The bite on the head, neck and arms progress most quickly, because of the close proximity of CNS to these locations. Rabies may also be transmitted by organ or corneal transplantation. The virus enters the peripheral nerves after deposition in the bite wound. It gradually moves towards spinal cord and brain tissues where it multiplies in nerve cells. Later it moves to salivary glands.

Disease in animals:

• Dog:
  • Furious form
    • Animal becomes restless, nervous and aggressive
    • Excessive salivation and frothing at mouth
    • Dilatation of pupil and a non focusing stare
    • Dog holds the tail between hind legs
    • Tendency to bite
  • Paralytic/dumb form
• Dropped jaw (paralysis of lower jaw) and drooling of saliva
• Changes in barking due to paralysis of vocal cords
• Convulsions, muscular incoordination, abnormal posture and gait
• Swaying of hind quarters, ataxia, prostration, coma and death (respiratory/cardiac failure)

Disease in humans:

• During prodromal phase, the patients suffer from a low grade fever, anorexia, headache, bodyache, weakness and fatigue
• Excessive salivation, restlessness and abnormal behavior
• Painful laryngeal spasm, so that the patient refuses to drink water (Hydrophobia)
• Delirium and coma finally leads to death

Diagnosis:

• Fluorescent antibody test with corneal impression smear, as well as brain. FAT is highly specific and rapid test
• Identification of Negri bodies in the brain impression smear by Seller’s staining technique
• Virus isolation from body fluid or brain tissue and electron microscopy
• Molecular techniques and serological tests (IF, CF, HA, HI, NT, ELISA)

Treatment:

• Wound cleaning with a carbolic soap
• Application of antiseptics

Prevention and Control:

• Post exposure vaccination – Administration of (HRIG) human rabies immune globulin (20 IU/Kg body weight), and the administration of 4 doses of vaccine on days 0, 3, 7, and 14
• Human Diploid Cell Vaccine (HDCV) and Purified Chick Embryo Cell Vaccine (PCEC) are both used for “pre” and “post exposure”
• Pre exposure vaccination– 0, 7 and 28 days followed by annual booster.
• Use of modified live virus vaccines which are prepared by egg passage of flurry strain in chick embryo.
• Controlling stray dog population
• Vaccination of high risk personnel

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