Definition of Rabies – Basic microbiology, parasitology, and immunology; nature, reproduction, growth, and transmission of common microorganisms and parasites in Bangladesh; prevention including universal precaution and immunization, control, sterilization, and disinfection; and specimen collections and examination. Students will have an understanding of common organisms and parasites caused human diseases and acquire knowledge about the prevention and control of those organisms.
Definition of Rabies
It is an acute, highly fatal viral infection caused by a rhabdo virus which primarily infects the central nervous tissue and salivary glands of a wide range of mammals and most frequently transmitted to man by saliva through bites or licks which produces fatal encephalitis in man.
Epidemiological Features:
A) Occurrence: It occurs throughout the world except in develop countries. Rabies is endemic in Bangladesh.
B) Ecological triad:
a) Agent: Rabies virus (Lyssavirus type 1) it is RNA virus
b) Host: Rabies virus can infect all mammals. Man is infected accidentallyub
c) Environment: It may occur at any time but is more prevalent in the summer months
C) Natural history:
a) Reservoir: Stray and pet dogs, cats, fox, wolf, jackal, hyena etc
b) Source of infections: saliva of the rabid animals.
c) Mode of transmission:
- Animal bites: By rabid dog bites
- Licks: Saliva comes in to direct contact with mucosa or fresh skin wounds
- Human to human Transmission by bite is theoretically possible and evidence is also present
- Others: Rarely, by inhalation of virus containing aerosol or transplantation of an infected organ.
d) Incubation period: Commonly 3-8 weeks, but may vary from 4 days to many years
Pathogenesis of Rabies
Bite of a rabid animal
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Rabies viruses are introduced into susceptible host
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Initially multiply in the local muscles
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Infects sensory neurons
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Travel via the nerves through retrograde axonal flow
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Reach the CNS
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Start multiplying with in the nerve cells.
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Encephalitis develops with damage of nerve cells
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Produce neurological signs and symptoms of rabies
Main reservoirs of Rabies virus;
1. Dogs (99% cases in Bangladesh)
2. Mongoose
3. Jackal
4. Fox
5. Wolf
6. Cat
7. Hyena
8. Vampire bat.
Modes of Transmission of Rabies:
1. Animal bites.
2. Licks.
3. Aerosols of bat secretions containing rabies virus.
4. Person to person.
- Child biting to parents
- Corneal & organ transplantation
Clinical Features:
A) Prodromal symptoms:
a) General:
- Headache
- Sore throat
- Slight fever for 3-4 days
b) Local: Paraesthesia (pain and tingling) at the site of the bite 80% patient complain
B) Systemic manifestation:
a) Furious rabies (seen in most patients):
- Sympathetic system:
✓ Dilation of the pupil
✓ Increase sweating
✓ Increase salivation
✓ Increase lacrimation
- Motor system: Increase reflexes and muscle spasm
- Mental change:
✓ Anxious
✓ Anger
✓ Irritable
✓ Fear of death
✓ Depression
✓ Delusion and hallucination may developed accompanied by spitting, biting and mania
- Sensory system: Intolerant to noise bright light a cold draught of air, aerophobia may present
b) Paralysis and death: Death may occur due to respiratory paralysis.
Lab, diagnosis of Rabies:
Principle;
Diagnosis is based on the detection of viral Ag in CNS / skin by immuno-fluorescence and Negri bodies in postmortem
For human;
- Fluorescent – Ab staining of biopsy specimen
- Isolation of virus from saliva, spinal fluid and brain tissue.
- Rise in titer of antibody.
- Negri bodies – in corneal scraping and brain tissue
For animal: The specimen is brain tissue. The tests are –
- Fluorescent Ab to Rabies virus
- Staining for Negri bodies
- Cell culture
Management of Human Rabies;
Wound management;
A. Cleaning of the wound.
B. Chemical treatment by alcohol or tincture iodine.
C. Suturing if needed.
D. Antibiotics and anti-tetanus measures.
Post-exposure prophylaxis:
A. Passive; Human rabies immunoglobulm.
Types of Rabies antibody.
- Rabies immunoglobulin human.
- Anti-rabies serum equine.
B. Active;
Human diploid cell vaccine;
- Dose 1 ml (0,3,7,14 and 28th day; a booster is recommended by WHO at 90th day)
Inactivated sheep brain vaccine;
- Slight risk – 2 ml x 7 days
- Moderate – 5 ml x 14 days
- Great risk – 10 ml x 14 days
Rabies can be controlled in the following way:
1. Licensing and vaccination of domestic dogs
2. Killing of stray dogs
3. Monitoring of reservoir hosts
4. Control and quarantine of imported animals
5. Vaccination of at risk animals and man (pre exposure prophylaxis)
6. Post exposure measurement (local treatment of wound and immunization)
7. Health education of people regarding the care of dogs and prevention of rabies.
Rabies vaccine.
Rabies vaccine; 3 types of rabies vaccines are commonly used.
1. Nervous tissue vaccine (NTV) – derive from adult animal (sheep) nervous tissue! DA
2. Duck embryo vaccine (DEV).
3. Cell culture vaccine – Human diploid cell culture vaccine (HDCV) & tissue culture vaccine.
Nerve tissue vaccine;
1. Nerve tissue vaccine is widely used specially in the 3rd world countries.
2. Dose schedule of the vaccine depends on the degree of risk of rabies.
- Slight risk – 2 ml x 7days.
- Moderate – 5 ml x 14 days.
- Great risk- 10 ml x 14 days.
Technique of administration: The ideal site is anterior abdominal wall.
Human diploid cell vaccine;
1. Dose: 1 ml (0, 3, 7, 14, 28 & 90 days).
2. Technique of administration: Intramuscular in deltoid muscle.
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