1. RABIES
• Rabies (Latin rabere, rage or madness) is caused by a
number of different strains of highly neurotropic
viruses.
• Most belong to a single serotype in the genus
Lyssavirus (Greek lyssa, rage or rabies), family
Rhabdoviridae.
• The bullet-shaped virion contains a single-strand RNA
genome.
• Most wild animals can become infected with rabies,
but susceptibility varies according to species. Dogs
Foxes, coyotes, and wolves are the most susceptible .
• Intermediate are skunks, raccoons, insectivorous bats,
and bobcats, whereas opossums are quite resistant.
2. • Worldwide almost all cases of human rabies are attributed to dog bites.
• In developing countries, where rabies is still endemic, rabies accounts for up to 40,000
deaths per year.
• In the United States, raccoons, skunks, and bats account for 83% of all animal cases.
• Occasionally other domestic animals are responsible for transmission of rabies to humans.
• It should be noted however, that not all rabid animals exhibit signs of agitation and
aggression (known as furious rabies).
• In fact, paralysis (dumb rabies) is the more common sign exhibited by rabid animals.
3. • The virus multiplies in the salivary glands of an infected host.
• It is transmitted to humans or other animals by the bite of an infected animal whose saliva
contains the virus;
• By aerosols the virus can be spread in caves where bats dwell; or by contamination of
scratches, abrasions, open wounds, and saliva from an infected animal.
• After inoculation, the virion's envelope spike attaches to the plasma membrane of nearby
skeletal muscle cells, which the virus enters.
• Multiplication of the virus then occurs. When the concentration of the virus in the muscle is
sufficient, the virus enters the nervous system through un myelinated sensory and motor
neuron .the binding site is the nicotinic acetylcholine receptor.
4. • The virus spreads 8 - 20 mm per day until it reaches the spinal cord, when the first specific
symptoms of the disease-pain or paresthesia at the wound site-may occur.
• A rapidly progressive encephalitis develops as the virus quickly disseminates through the
central nervous system.
• The virus then spreads throughout the body along the peripheral nerves, including those in
the salivary glands, where it is shed in the saliva.
• With in brain neurons, the virus produces characteristic Negri bodies, masses of virions or
unassembled viral subunits that are visible in the light microscope.
• Symptoms of rabies in humans usually begin 2 to 16 weeks after exposure and include
anxiety, irritability, depression, fatigue, loss of appetite, fever, and a sensitivity to light and
sound.
• The disease quickly progresses to paralysis. In about 50% of all cases, intense and painful
spasms of the throat and chest muscles occur when the victim swallows liquids
5. • .
• The mere sight, thought, or smell of water can set off spasms. Consequently, rabies has
been called hydrophobia (fear of water).
• Death results from destruction of the regions of the brain that regulate breathing.
• Safe and effective vaccines (human diploid-cell rabies vaccine [HDCV] or rabies vaccine
adsorbed [RVA]) against rabies are available
• however, to be effective they must be given soon after the person has been infected.
• Veterinarians and laboratory personnel, who have a high risk of exposure to rabies, usually
are immunized every 2 years and tested for the presence of suitable antibody titer.
6. • ; Prevention and control involve pre exposure vaccination of dogs and cats, post exposure
vaccination of humans, and pre exposure vaccination of humans at special risk, including
persons spending a month or more in countries where rabies is common in dogs.
• Some states and countries (e.g., Hawaii and Great Britain) retain their rabies-free status by
imposing quarantine periods on any entering dog or cat.
• If an asymptomatic, unvaccinated dog or cat bites a human, the animal is typically
confined and observed by a veterinarian for at least 10 days.
• If the animal shows no signs of rabies in that time, it is determined to be uninfected.
• Animals demonstrating signs of rabies are killed, and brain tissue is submitted for rabies
testing.
7. • Post exposure prophylaxis-rabies immune globulin for passive immunity and rabies
vaccine for active immunity is initiated to exploit the relatively long incubation period of
the disease.
• This is usually recommended for anyone bitten by one of the common reservoir species
(raccoons, skunks, foxes, and bats), unless it is proven that the animal was uninfected.
• Once symptoms of rabies develop in a human, death usually occurs.
