Rabies


Rabies is an infectious disease of animals which is a member of a group of
viruses constituting the family Rhabdoviridae. The virus particle is covered in
a fatty membrane, is bullet-shaped, 70 by 180 nanometres and contains a single
helical strand of ribonucleic acid (RNA).

Although rabies is usually spread among domestic dogs and wild carnivorous
animals, all warm-blooded animals are susceptible to infection. The virus is
often present in the salivary glands of infected animals, referred to as rabid,
and is excreted in the saliva. The bite of the infected animal easily
introduces the virus into a fresh wound. In humans, rabies is not usually spread
from man to man, rather the majority of infections occur from rabid dogs. After
a person has been inoculated, the virus enters small nerve ends around the site
of the bite, and slowly travels up the nerve to reach the central nervous system
(CNS) where it reproduces itself, and will then travel down nerves to the
salivary glands and replicate further. The time it takes to do this depends on
the length of the nerve it must travel - a bite on the foot will have a much
lengthier incubation period than a facial bite would. This period may last from
two weeks to six months, and often the original wound will have healed and been
forgotten by the time symptoms begin to occur.

Symptoms in humans present themselves in one of two forms: ‘furious rabies\', or ‘
dumb rabies\'. The former is called such because of the severe nature and range
of the symptoms. The virus, upon reaching the CNS will present the person with
headache, fever, irritability, restlessness and anxiety. Progression may occur
on to muscle pains, excessive salivation, and vomiting. After a few days or up
to a week the person may go through a stage of excitement, and be afflicted with
painful muscle spasms which are sometimes set off by swallowing of saliva or
water. Because of this the afflicted will drool and learn to fear water, which
is why rabies in humans was sometimes called Hydrophobia. The patients are also
extremely sensitive to air or drafts blown on their face. The stage lasts only
fews days before the onset of a coma, then death. Dumb rabies begins similarly
to furious rabies, but instead of symptoms progressing to excitement, a steady
retreat and quiet downhill state occurs. This may be accompanied with paralysis
before death. Rabies diagnosis in this type of cases can be missed.
Unfortunately with both furious and dumb rabies, once the disease has taken hold
clinically, rapid and relentless progression to invariable death occurs despite
all known treatments.

Treatment for the recently infected would include washing the wound with soap,
detergent, and water. Then an anti-rabies serum can be administered to humans.
Alternative to the serum, an effective and intensive treatment after infection
can be obtained through the use of a killed virus vaccine, because of the
unusually long incubation period. The vaccine, a Human Diploid Cell Vaccine
(HDCV) is grown in human fibroblasts (the principal nonmotile cells of
connective tissue) and is quite safe for human use. When used, the vaccine did
dramatically cut the rabies death toll. Previous killed virus vaccines, which
had been made from infected neural tissue, were not completely effective at
immunisation and had caused adverse side effects.

Since contact with wild animals is the main source of infection for humans and
their pets, avoidance of any direct contact with these animals reduces the risk
of being bitten quite dramatically. Raccoons that are wandering in the daylight
hours, or any animal that seems ‘friendly\' should be avoided as well. Other
high-risk animals include skunks, foxes, jackals, wolves, as well as an odd
association with bats.

Category: Science