Rabies: A Fatal Yet Preventable Zoonotic Disease
Introduction
Rabies is an ancient and universally feared viral disease, often associated with dog bites and
popularly referred to as hydrophobia. It is a highly fatal zoonotic disease affecting the central
nervous system of all warm-blooded animals, including humans. Despite being vaccine-
preventable, rabies continues to cause thousands of deaths annually, particularly in developing
countries where dog-mediated transmission remains unchecked.
Definition and Causative Agent
Rabies is an acute, progressive, and almost invariably fatal viral encephalomyelitis caused by
Lyssavirus type 1, a bullet-shaped RNA virus belonging to the family Rhabdoviridae. It
primarily affects warm-blooded animals and is transmitted to humans through the saliva of
infected animals, mainly via bites or scratches. The virus enters peripheral nerves and travels
centripetally to the central nervous system, leading to fatal inflammation of the brain.
There are multiple serotypes of the rabies virus. While Type 1 causes classical rabies in humans
and animals, other serotypes (2, 3, and 4) may also cause disease but are antigenically different.
Epidemiology
Rabies is both enzootic (endemic in animals) and epizootic (can cause outbreaks), occurring in
over 150 countries. It is a notifiable disease due to its high fatality and public health
importance. An estimated 55,000 deaths occur annually worldwide due to rabies, with the
majority in Asia and Africa.
In India, about 20,000 deaths occur annually, mainly in rural areas, accounting for nearly 36%
of global rabies deaths. Children under 15 years are particularly vulnerable due to their closer
proximity to dogs and lack of awareness about wound care. The primary reservoir of human
rabies is domestic dogs, although wild animals and bats are emerging sources in some regions.
Host and Agent Factors
All warm-blooded animals, including humans, are susceptible to rabies. The virus is neurotropic
and targets the nervous system. It has two major antigens:
Glycoprotein (G protein) on the viral envelope: Stimulates
neutralizing antibody production.
Nucleoprotein (N protein): Used in diagnostics.
The source of infection in humans is saliva of rabid animals, particularly dogs, but also includes
cats, bats, and other mammals. The virus can be present in saliva 3–4 days before clinical
symptoms appear and until death.
Incubation Period
The incubation period in humans is typically 1–3 months, but may range from a few days to
several years, depending on:
Site and severity of the bite
Distance from the CNS
Host immunity
Amount of virus inoculated
Shorter incubation is associated with bites on the face, head, or neck due to proximity to the
brain.
Clinical Features in Humans
Rabies in humans progresses through several stages:
1. Prodromal Phase
Lasts 2–4 days
Symptoms: Fever, malaise, headache, sore throat, and pain/tingling at
the site of bite
2. Excitation or Furious Phase
Anxiety, confusion, agitation
Hallmark signs: Hydrophobia (fear of water), aerophobia (fear of
air drafts) due to painful pharyngeal spasms
Hypersalivation, dilated pupils, abnormal behavior
3. Paralytic or Dumb Phase
Gradual paralysis, respiratory failure
Coma and death within 2 to 3 days (can be up to 5–6 days in rare
cases)
Rabies is almost always fatal once clinical symptoms appear. Only a few isolated survivors have
been documented.
Diagnosis
Clinical diagnosis is usually sufficient in symptomatic cases with history of animal exposure.
Laboratory methods include:
1. Fluorescent Antibody Test (FAT): Gold standard; detects viral
antigen in brain tissue.
2. Mouse Inoculation Test: Intracerebral inoculation of mice with
suspected tissue.
3. Corneal Smear Test: Detects viral antigen in corneal impressions.
4. Skin Biopsy (Neck): Demonstrates Negri bodies and viral antigen.
Prevention and Control
Rabies is 100% preventable with timely and appropriate prophylaxis. Prevention is categorized
into:
1. Post-Exposure Prophylaxis (PEP)
Essential for all individuals exposed to potentially rabid animals.
Steps include:
Wound Care: Immediate and thorough washing of wounds with soap
and water for at least 15 minutes, followed by antiseptic application.
Vaccination: WHO-recommended intramuscular (Essen, Zagreb) or
intradermal schedules.
Rabies Immunoglobulin (RIG): Given for Category III exposures
(deep wounds, scratches, saliva contact with mucosa, etc.)
Exposure PEP
Example
Category Measures
I Touching, feeding animals None
II Minor scratches without bleeding Vaccine
III Bites, scratches, saliva contact with Vaccine +
Exposure PEP
Example
Category Measures
mucosa RIG
2. Pre-Exposure Prophylaxis (PrEP)
Recommended for:
Laboratory workers
Veterinarians
Travelers to high-risk areas
Children in endemic zones
Schedule: Days 0, 7, and 21 or 28 (IM or ID route)
3. Rabies Control in Animals
Since 90% of human rabies in India is from dog bites, canine rabies control is crucial. Measures
include:
Dog vaccination at 3 months of age followed by annual boosters
Registration and licensing of domestic dogs
Stray dog population control (sterilization)
Public awareness and education
Rabies in dogs manifests as:
Furious rabies: Aggression, biting without provocation
Dumb rabies: Paralysis and lethargy
Vaccines and Immunoglobulin
Modern vaccines: Cell-culture vaccines (CCEV, PCECV) and
embryonated egg-based vaccines
Immunoglobulin: HRIG (20 IU/kg) and ERIG (40 IU/kg) infiltrated
around the wound
Adverse Effects and Contraindications
Rabies vaccines are generally safe. Minor side effects include fever, pain, and local reactions.
Severe allergic reactions are rare.
Contraindications apply only in PrEP, not PEP, as rabies is invariably fatal if untreated.
Conclusion
Rabies continues to be a major public health concern in many parts of the world, especially in
Asia and Africa. With early wound care, timely post-exposure vaccination, and control of
rabies in dogs, human rabies is entirely preventable. Mass awareness, better access to vaccines,
and effective dog population management are essential steps toward achieving zero rabies
deaths in the future.
