Model Answer
0 min readIntroduction
Rabies, a neglected tropical disease, remains a major public health problem globally, particularly in Asia and Africa, with India bearing a significant burden. It is a fatal viral disease affecting mammals, transmitted primarily through the saliva of infected animals, most commonly dogs. The causative agent, *Rabies lyssavirus*, a member of the Rhabdoviridae family, attacks the central nervous system, leading to a devastating and invariably fatal outcome if left untreated. According to the World Health Organization (WHO), approximately 59,000 human deaths occur annually due to rabies, with over 95% of these cases resulting from dog bites. This answer will comprehensively detail the etiology, pathogenesis, clinical symptoms, diagnosis, and control of rabies in dogs.
Etiology of Rabies
The etiology of rabies revolves around the *Rabies lyssavirus* (RABV), a bullet-shaped virus. Key aspects include:
- Viral Classification: Family Rhabdoviridae, genus *Lyssavirus*. RABV is the most common species.
- Reservoir Hosts: Primarily canids (dogs, wolves, foxes), but also bats, raccoons, skunks, mongooses, and jackals.
- Transmission: Primarily through the bite or scratch of an infected animal. Less commonly, through aerosol transmission (in bat caves) or corneal transplantation.
- Incubation Period: Highly variable, ranging from days to months, even years in rare cases, depending on factors like viral load, bite location, and individual immune status.
Pathogenesis of Rabies
The pathogenesis of rabies is a complex process involving several stages:
- Entry and Local Spread: The virus enters through the bite wound and replicates locally in muscle cells.
- Neuronal Invasion: The virus then travels along peripheral nerves to the central nervous system (CNS). This is a slow process, contributing to the long incubation period. Retrograde transport along axons is crucial.
- CNS Infection: Once in the CNS, the virus replicates in neurons, particularly in the hippocampus, cerebellum, and brainstem.
- Viral Shedding: Infected animals begin to shed the virus in their saliva, making them infectious.
- Clinical Signs: Neurological dysfunction results in the characteristic clinical signs of rabies.
Table 1: Pathogenesis Stages
| Stage | Description |
|---|---|
| Entry & Local Replication | Virus enters through bite wound, replicates in muscle cells. |
| Neuronal Invasion | Virus travels along peripheral nerves to CNS. |
| CNS Infection | Replication in neurons, causing neurological dysfunction. |
| Viral Shedding | Virus shed in saliva, making animal infectious. |
Clinical Symptoms in Dogs
Rabies in dogs presents in two main forms: furious and paralytic (dumb) rabies. The furious form is more common.
- Furious Rabies:
- Restlessness, aggression, biting at air or objects.
- Hypersensitivity to stimuli.
- Muscle tremors, seizures.
- Excessive salivation ("foaming at the mouth").
- Difficulty swallowing (dysphagia).
- Paralysis may occur later.
- Paralytic (Dumb) Rabies:
- Depression, lethargy.
- Paralysis, often starting in the hind limbs and progressing forward.
- Difficulty swallowing.
- Drooling.
- Progressive paralysis leading to death.
Diagnosis of Rabies
Diagnosis is challenging, particularly in live animals. Post-mortem diagnosis is more reliable.
- Ante-mortem Diagnosis: Direct Rapid Antigen Detection (DRAD) test on saliva or skin biopsies is increasingly used. Polymerase Chain Reaction (PCR) is highly sensitive but requires specialized equipment.
- Post-mortem Diagnosis:
- Fluorescent Antibody Test (FAT): The gold standard, detects rabies virus antigen in brain tissue.
- Negri Bodies: Intranuclear inclusions visible under light microscopy (though not always present).
- PCR: Detects viral RNA in brain tissue.
Control of Rabies
Rabies control requires a multi-faceted approach:
- Mass Dog Vaccination: This is the most effective intervention. India's National Rabies Control Programme (NRCP) aims to achieve 70% dog vaccination coverage.
- Post-Exposure Prophylaxis (PEP): Immediate wound cleansing and administration of human rabies immunoglobulin (HRIG) and rabies vaccine.
- Public Awareness Campaigns: Educating the public about rabies transmission and prevention.
- Stray Dog Management: ABC (Animal Birth Control) programs to control stray dog populations.
- Surveillance: Monitoring rabies cases in animals and humans.
- International Collaboration: Sharing information and resources with other countries.
Example: The "Blue Cross of India" is actively involved in rabies vaccination and ABC programs in various cities across India.
Conclusion
Rabies remains a significant public health challenge, particularly in developing countries. Effective control requires a comprehensive approach encompassing mass dog vaccination, prompt PEP following exposure, public awareness campaigns, and responsible dog management. While significant progress has been made, sustained efforts are crucial to eliminate rabies as a public health problem, aligning with the WHO’s Global Rabies Elimination Roadmap. Continued investment in research and development of improved diagnostic tools and vaccines is also essential for achieving long-term success.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.