Introduction
Rabies is a deadly but preventable viral disease that affects both humans and animals. It is caused by the Rabies lyssavirus and spreads primarily through the bite or scratch of an infected animal. Despite its severity, rabies is 100% preventable with timely vaccination and proper care.
In this blog, we’ll explore:
• How rabies spreads
• Clinical features in humans and dogs
• Diagnosis, prevention, and treatment
• Frequently asked questions (FAQs)
Morphology of Rabies Virus
Shape: Bullet-shaped
Structure:
• Enveloped virus with a helical nucleocapsid
• Single-stranded, negative-sense RNA genome
Major Antigens:
• Glycoprotein G → Helps the virus attach to host cells
• Nucleoprotein (N) → Used for laboratory diagnosis
Street vs Fixed Virus
Street Virus:•
• Freshly isolated from wild animals
• Long and variable incubation periods
• Produces intracytoplasmic inclusion bodies
Fixed Virus:
• Serially propagated in rabbits
• Short incubation period (4–6 days)
• Does not produce inclusion bodies, multiply in extraneural tissues, or infect salivary glands
• Used for vaccine preparation
Pathogenesis of Rabies
1) Entry
Bite exposure:
• Rabid dogs → Cause 99% of cases
• Other animals → Bats, foxes, raccoons, skunks, mongooses
Non-bite exposure:
• Saliva contact with mucosa or open wounds
• Aerosol inhalation (important for lab workers)
• Cornea or organ transplantation
Rabies does NOT spread through:
• Human-to-human bites or saliva
• Eating raw meat/milk of infected animals
• Bites from rodents
• Petting a rabid animal
2) Local Replication
Virus replicates at the bite site in muscle cells
3) Neural Spread
Virus binds to acetylcholine receptors and travels to the CNS via peripheral nerves
4) CNS Involvement
Rapid spread to the hippocampus, brainstem, and cerebellum
5) Centrifugal Spread
Virus moves from the CNS to other organs (salivary glands, cornea, skin)
6) Shedding in Saliva
Facilitates transmission through bites
Clinical Features of Rabies
Incubation Period
• 20–90 days (range: 1 week to 1 year)
Shorter in:
• Children
• Head, neck, and upper limb bites
• Severe lacerations
• High viral dose & virulence
Phases of Rabies in Humans
1) Prodromal Phase (2–10 days)
• Fever
• Nausea, vomiting
• Burning sensation at the bite site
2) Acute Neurological Phase (2–7 days)
πΉ Furious (Encephalitic) Rabies (80%)
• Hyperexcitability → Anxiety, agitation, hallucinations
• Lucid intervals → Shorten as disease progresses
• Autonomic dysfunction → ↑ Salivation, ↑ Lacrimation, Goosebumps
• Hydrophobia & Aerophobia → Painful throat spasms
πΉ Paralytic (Dumb) Rabies (20%)
• Flaccid paralysis → Starts in bitten limb
• Facial muscle weakness
• No hydrophobia or excitability
3) Coma & Death
Fatal within 1–2 weeks due to respiratory/cardiac failure
Lab Diagnosis of Rabies
π¬ Lab Tests for Rabies Diagnosis
1) Direct Fluorescent Antibody Test (dFAT) [Gold Standard]
• Detects viral antigens in brain tissue
• Used for postmortem diagnosis
2) Negri Bodies Detection
• Seen in hippocampus & cerebellum
• Identified by Seller’s stain
3) RT-PCR & Virus Isolation
• Detects viral RNA from CSF, saliva, or nuchal skin biopsy
4) Serology (Antibody Detection)
• ELISA & Neutralization tests for anti-rabies antibodies
• Not useful in early stages
Treatment of Rabies
• Once symptoms appear, rabies is almost always fatal
Post-Exposure Prophylaxis (PEP)
• For Category II & III bites
• Vaccine Schedule (IM/ID): Day 0, 3, 7, 14 (28 for immunocompromised)
• Rabies Immunoglobulin (RIG) for Category III bites
• Milwaukee Protocol (Experimental)
• Induced coma + antivirals
• Limited success in survivors
Rabies in Dogs
90% of human rabies cases come from dog bites
πΉ Furious Rabies
• Sudden aggression
• Restlessness, biting
• Excessive salivation
πΉ Paralytic Rabies
• Gradual paralysis
• Facial muscle weakness
• Coma & Death
Prevention of Rabies
1. Rabies Vaccine
• Pre-exposure (PrEP) → High-risk groups (Veterinarians, lab workers)
• Post-exposure (PEP) → After bite exposure
Vaccine Schedules
• Pre-exposure → Day 0 & 7
• Post-exposure → Day 0, 3, 7, 14 (28 if needed)
2. Rabies Immunoglobulin (RIG)
• Neutralizes virus at the wound site
• Administered on Day 0
3. Wound Care
• Wash wound with soap for 15 minutes
• Apply antiseptics (povidone-iodine, alcohol)
National Guidelines for Rabies Prophylaxis (India)
India follows updated National Rabies Prophylaxis Guidelines aligned with WHO recommendations to prevent rabies effectively.
1. Post-Exposure Prophylaxis (PEP):
Wound Care: Wash thoroughly with soap & water for 15 min, apply antiseptics (povidone-iodine).
Vaccination:
• Intramuscular (IM): Days 0, 3, 7, 14
• Intradermal (ID): Days 0, 3, 7
Rabies Immunoglobulin (RIG) for Category III bites:
ERIG: 40 IU/kg | HRIG: 20 IU/kg (infiltrate around wounds).
2. Pre-Exposure Prophylaxis (PrEP):
• Recommended for high-risk groups (veterinarians, lab workers, children in endemic areas).
• Vaccine (ID): Two-site Day 0 & 7
3. Surveillance & Awareness:
• Strengthening rabies surveillance & public education on responsible pet care and timely vaccination.
For full guidelines, visit NCDC
FAQs on Rabies
• Can rabies be cured after symptoms appear?
No. Once symptoms appear, rabies is almost always fatal.
• Do I need a vaccine for a minor scratch by a pet dog?
Yes. Any scratch that breaks the skin needs medical attention.
• Can rabies spread by touching a rabid animal?
No. Only spreads through bites, saliva, or open wounds.
• How long does the virus survive outside the body?
The virus dies within hours in air or sunlight.
External Links and Resources
Trusted Sources:
World Health Organization (WHO) — Rabies
Centers for Disease Control and Prevention (CDC)
Global Alliance for Rabies Control (GARC)
Conclusion
Rabies is a preventable but fatal disease. Immediate wound care, vaccination, and awareness can save lives. With WHO’s "Zero by 30" initiative, we aim to eradicate human rabies deaths by 2030.
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