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RRabiesABIES
Rabies is a viral brain disease that is almost always fatal if it
is not prevented with prompt treatment. The disease, which
typically spreads to humans from animals through a scratch or
a bite, causes inflammationof the brain. The disease is also
called hydrophobia (meaning fear of water) because it causes
painful muscle spasms in the throat that prevent swallowing.
In fact, this is what leads to most fatalities in untreated cases:
victims become dehydrated and die. Carriers of rabies include
dogs, cats, bats, skunks, raccoons, and foxes; rodents are not
likely to be infected. About 70% of rabies cases develop from
wild animal bites that break the skin. Though a vaccineused
first in 1885 is widely used, fatalities still occur due to rabies.
Most fatalities take place in Africa and Asia, but some also
occur in the United States. The cost of efforts to prevent rabies
in the United States may be as high as $1 billion per year.
While many animal diseases cannot be passed from ani-
mal to man, rabies has long been known as an easy traveler
from one species to the next. The disease was known among
ancient people. The very name rabies, Latin for rage or mad-
ness, suggests the fear with which early men and women must
have viewed the disease. For centuries there was no treatment,
and the disease was left to run its rapid course leading to death.
Rabies is described in medical writings dating from 300
B.C., but the method of transmission or contagion was not rec-
ognized until 1804. In 1884, the French bacteriologist Louis
Pasteurdeveloped a preventive vaccine against rabies, and
modifications of Pasteur’s methods are still used in rabies
therapy today. The Pasteur program, or variations of it, has
greatly reduced the fatalities in humans from rabies. Modern
treatment, following a bite by a rabid or presumed rabid ani-
mal, consists of immediate and thorough cleansing of the bite
wound and injection into the wound and elsewhere of hyper-
immune antirabies serum. Post exposure treatment consists of
five injections of vaccine given over a one-month period,
along with one dose of rabies immune globulin injected near
the wound and intramuscularly.The standard vaccine contains inactivated rabies virus
grown in duck eggs. It is highly effective but causes neu-
roparalysis in about one in 30,000 persons receiving it. In the
1970s, a new vaccine was developed in France and the United
States that contains virus prepared from human cells grown in
the laboratory. This vaccine is safer and requires a shorter
course of injections. With the widespread use of vaccine,
rabies cases in the U.S. declined to fewer than five per year.
The transmission of rabies is almost invariably through
the bite of an infected animal. The fact that the virus is elimi-
nated in the saliva is of great significance, and unless saliva is
introduced beneath the skin, the disease is seldom transmitted.
The virus has been demonstrated in the saliva of dogs 3–8
days before the onset of symptoms. However, it has also been
reported that only about 50–60% of the infected dogs shed the
virus in the saliva. Rare cases of rabies have been reported
where only clawing and scratching occurred, or where the skin
was contaminated with saliva. The virus is most concentrated
in the central nervous system and saliva, but it has also been
demonstrated in various organs of the body and milk from
infected animals.
In humans, the rabies virus, in addition to entering the
body by the usual route through skin broken by a bite or
scratch, can enter the body through intact mucous membranes,
can be inhaled as an aerosol, and can be transplanted in an
infected corneal graft. These four cases are the only virologi-
cally documented examples of transmission of rabies from one
person to another. Vertical transmission from mother to fetus
and from lactating mother to suckling young has been
described in nonhuman mammals.
The incubation period in natural cases of rabies is vari-
able. In general, the quantity of virus introduced into the
wound is correlated with the length of incubation before
symptoms occur. In dogs, the minimum period is ten days, the
average 21–60 days, but may be as long as six months. In man,
the incubation period is one to three months, with the mini-
mum of ten days.womi_R 5/7/03 8:17 AM Page 475