Microbiology of Rabies Virus

October 12, 2010 | 9:41 pm | Microbiology | No Comment

Properties:

Belongs to genera “lyssavirus” of family “rhabdoviridae”
Bullet shaped
Nucleocapsid shows helical symmetry
ssRNA (single stranded RNA) virus
Outer lipoprotein envelope contains protruding hemagglutinating peplomer spikes

Street and Fixed virus Comparison:

Basis of difference	Street virus	Fixed virus
Definition	Freshly isolated viruses from natural human or animal infection that has not undergone any modification in the laboratory	Strains adapted to laboratory animals by several serial intracerebral passages in rabbits
Neurotropism	No	Yes
Incubation period	Long (21-60 days in dogs)	Shortened (4-6 days)
Negri bodies	Present	Usually absent

Epidemiology:

Sylvatic rabies: occur in wild animals like skunks, jackals, raccoons, foxes, wolves, mongoose, bats, etc.
Urban rabies: transmitted by domestic animals like dogs, cats, horses, cattle
Modes of transmission: Animal bite, scratch, inhalation of contaminated aerosols and transplantation of infected corneas (rare)

Continents	Animals involved
Asia	Dog
Middle east	Wolf, dog
Africa	Dog, mongoose, antelope
Europe	Fox, Bats
North America	Fox, skunk, raccoon, insectivorous and herbivorous bats
South America	Dog, vampire bats

Pathogenesis:

1. Inoculation of virus
2. Multiplication in muscle or connective tissue locally (at the site of inoculation)
3. Invasion of peripheral nerve fibers at the neuromuscular junction (NMJ)
4. Entry into the peripheral nerves through NMJ
5. Ascend to CNS (spinal cord and brain) via retrograde transport
6. Multiplication in the grey matter of brain
7. Propagation via afferent neurons to peripheral tissues including salivary gland from which the virus is excreted
8. Incubation period depends on the portal of entry, dose of inoculum and severity of the wound

Clinical features:

Prodormal period (1-10 days): Headache, malaise, fever, anxiety, anorexia, sore throat and myalgia
Clinical disease: Hydrophobia, spasms, hyperexcitability
With disease progression: seizures, disorientation, delirium, flaccid paralysis, death due to involvement of nervous, pulmonary and cardiac systems.

Laboratory Diagnosis:

A video of Laboratory Diagnosis of Rabies Virus

Diagnosis in man:

Rapid immunofluorescence tests to detect virus, viral nucleic acids and viral products in samples of sliva, corneal impression and smears of skin biopsies
Test for detection of antibodies to the virus in the serum of unvaccinated individual
Demonstration of negri bodies in brain
Isolation of virus by mouse inoculation with brain, CSF, saliva and urine

Diagnosis in animal:

A part of brain of the rabid animal is preserved in 50% glycerol for isolation of virus
Remaining part is preserved in Zenker’s fixative for demonstration of negri bodies using Seller’s technique.

Immunization:

A. Human Rabies Immunoglobulin serum (HRIG)

B. Vaccine: Due to high risk of neuroparalytic accidents with neural vaccines, non-neural vaccines are being increasingly used these days.

Neural vaccines:

Semple vaccine
BPL (Betapropriolactone) vaccine
Infant brain vaccine

Non-neural vaccines:

Inactivated: Duck egg vaccine and HDCV
Live attenuated: Chick embryo vaccine (LEP of 40-50 and HEP of 180)

Subunit vaccine: Recently developed recombinant vaccine is in experimental stage

Prophylaxis in Nepal

If a person has completed a pre-exposure rabies series and is exposed to a possibly rabid animal then, 2 shots as a booster, 3 days apart
If a person has not had pre-exposure rabies injections and is exposed to a possibly rabid animal then human Rabies Immune Globulin (HRIG) injected around the wound; 5 injections of rabies vaccine on days 0, 3, 7, 14, and 28

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Last updated: October 12, 2010