Rabies

Question 1

What is the scientific name and family?

Answer 1

Lyssavirus of Rhabdoviridae family

Question 2

Characteristics

Genome, envelope?

Answer 2

ssRNA enveloped virus, characteristic bullet-shaped apperance with spike projections

Question 3

Describe the pathogenesis

Answer 3

• Virus replicates in striated or connective tissue at site of inoculation (usually dog bite)
• Enters peripheral nerves through NMJ
• Spreads to CNS in endoneurium of Schwann cells
• There is widespread CNS involvement terminally

Acute infection of CNS and is almost invariably fatal

Question 4

What is the major source in urban areas?

Answer 4

Domestic dog (where there are no immunisation programmes)

Question 5

How is it transmitted?

Answer 5

Bite of a rabid animal (usually dog)
May also be inhaled (in bat-infested caves)

Question 6

What are the 3 phases?

Answer 6

1. Prodromal phase
2. Excitation phase
3. Paralytic phase

Question 7

What are the clinical features of the Prodromal phase?

Answer 7

In a day or two:
- Pain and paraesthesia in area of bite
- Gastrointestinal symptoms
- Upper respiratory symptoms
- Irritability
- Apprehension
- Sense of impending death
- Hydrophobia

Question 8

What are the clinical features of the Excitation phase?

Answer 8

• Hyperventilation
• Hyperactivity
• Disorientation
• Seizures

Question 9

What are the clinical features of the Paralytic phase?

Answer 9

• Lethargic and early paralysis (esp. in areas innervated by cranial nerves and in somatic muscles, bladders, bowels)
• Gradual involvement of cardiac muscles and paralysis of respiratory muscles lead to death

Question 10

How is it diagnosed?

Answer 10

• Histopathology - Negri bodies are pathognomonic
• Rapid PCR, virus antigen detection, direct fluorescent antibody test - corneal impressions or neck skin biopsy (widely used)
• Virus cultivation from saliva and infected tissue (most definitive)
• Serology - circulating antibodies appear slowly but usually present by time of onset of clinical symptoms

Question 11

What is the postexopsure prophylaxis?

Answer 11

• Wound treatment - bites and scratches should be thoroughly washed with soap and water
• Passive immunisation - human rabies immunoglobulin around area of wound and to be supplemented with IM dose to confer short term protection
• Active immunisation

Question 12

Describe the vaccine

Answer 12

• Human diploid cell vaccine (currently best vaccine available with efficacy rate of nearly 100% and rarely any severe reactions)
• Give IM/SC into deltoid area of upper arm in 5 doses spaced at days 0, 3, 7, 14, 30
• Dogs: inactivated vaccines

Question 13

How to control canine rabies?

Answer 13

• Stray dog control
• Vaccination of dogs
• Quarantine of imported animals