Rabies Virus

Question 1

Classification

Answer 1

Family: Rhabdovirae

Genus: Lyssavirus

Species: Rabies virus

Question 2

Characteristics

Answer 2

• Enveloped virus (bullet shaped)
• Helical nucleocapsid
• -ssRNA
• virion RNA polymerase
• cytoplasmic replication —> forms intracytoplasmic bodies (Negri bodies)

Question 3

Transmission

Answer 3

• Main reservoir is wild animals such as foxes, racoons, skunks and bats
• transmission to humans is usually by animal bite
• it is also transmitted by aerosols of bat’s saliva

Question 4

Pathogenesis

Answer 4

• binds to Nicotinic Acetylcholine receptors
• initially infects neurons at the post-synaptic motor endplate
• replicates in motor neurons
• retrograde movement of the virus along peripheral nerves (1 to 3mm a day)
• incubation period of weeks to months before symptoms appear
• travels to dorsal root ganglia —> then to brain
• after replicating in the brain, the virus migrated peripherally to the salivary glands, where it enters the saliva

> > when the animal is in the agitated state as a result of encephalitis, virus in the saliva can be transmitted via a bite

Question 5

Disease

Answer 5

• fever
• foaming in the mouth

Rabies = encephalitis

> > Furious rabies —> 80% cases

• hyperactivity
• hydrophobia
• sometimes aerophobia

Death occurs after a few days due to cardio-respiratory arrests

> > Paralytic rabies —> 20% cases —> less dramatic and longer course:

• muscles gradually become paralyzed (starting at the site of the bite)
• coma slowly develops
• death eventually occurs

!! There is a higher attack rate and shorter incubation period in persons bitten on the face or head. The lowest mortality occurs in those bitten on the legs !!

Question 6

Microbiological diagnosis

Answer 6

> > > Tissue can be stained with fluorescent antibody or with various dyes to detect cytoplasmic inclusions= Eosinophilic Negri bodies. ««
Found in:
- cerebellum (Purkinje cells)
- hippocampus (pyramidal cells)

• Rapid diagnosis - PCR
• cell culture too slow
• serologic test only for diagnosis in clinically ill patient

Question 7

Treatment and prevention

Answer 7

Treatment:

• no antiviral drug
• only symptomatic therapy —> May prolong life, but the outcome is almost always fatal
• passive immunization —> giving human rabies immunoglobulins, mostly into the wound made by the bite

Prevention:
- pre-exposure prevention of rabies consists of the vaccine only 
- post-exposure prevention consists of:
Washing the wound
Passive immunization 
Active immunization 

Prevention of rabies in dogs and cats by using a killed vaccine has reduced human rabies significantly