RABIES
INTRODUCTION:
Rabies is an infectious
disease of animals caused by a bullet-shaped, enveloped RNA virus, 180 x 75 nm.
Man is occasionally infected, and once infection is established in the CNS, the
outcome is almost invariably fatal.
HUMAN RABIES:
Is acquired from virus in
saliva entering a bite wound caused by an infected animal, usually a rabid dog.
The severity of the bite determines the risk of infection. The disease does not
usually spread from man to man.
Classification:
Rabies virus
belongs to the order Mononegavirales, viruses with a nonsegmented,
negative-stranded RNA genomes. Within this group, viruses with a distinct
"bullet" shape are classified in the Rhabdoviridae family, which
includes at least three genera of animal viruses, Lyssavirus,
Ephemerovirus, and Vesiculovirus. The genus Lyssavirus
includes rabies virus, Lagos bat, Mokola virus, Duvenhage virus, European bat
virus 1 & 2 and Australian bat virus.
Incubation:
After inoculation, the
virus enters small nerve endings at the site of the bite. The virus slowly
travels up the nerve to reach the CNS where it replicates and then travels down
nerves to the salivary glands where there is further replication. The time it
takes to do this depends upon the length of the nerve - a bite on the foot will
have a very much longer incubation period than a bite on the face. The
incubation period may last from two weeks to six months. Very often the
primary wound is healed and forgotten by the time of clinical presentation.
TREATMENT:
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1. Wash wound (soap, detergent and water) |
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2. Anti-rabies serum (human). Passive immunization. |
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3. Vaccine (intensive course). Active immunization. |
RABIES VACCINE:
A good but
expensive killed virus vaccine (Human Diploid Cell Vaccine, HDCV) grown
in human fibroblasts is available for safe use in man.
The unusually long incubation period of the virus permits the effective use of
active immunisation with vaccine post-exposure. When used, vaccine has
dramatically cut the rabies death rate. Supplied free by the State through
district surgeons in South Africa.
(Older killed virus vaccines, made from infected
neural tissues, were poorly immunogenic and had allergic encephalitic side
effects, but are still used in developing countries.)