Rabies (from a Latin word
meaning rage) is a viral disease that causes acute encephalitis in
people. In unvaccinated humans, rabies is almost invariably fatal once full-blown
symptoms have developed, but post-exposure vaccination can prevent
Transmission and symptoms
The stereotypical image
of an infected ("rabid") animal is a "mad dog"
foaming at the mouth, but cats, ferrets, raccoons, chipmunks, skunks,
foxes and bats also become rabid. Squirrels, other rodents and rabbits
are very seldom infected, perhaps because they would not usually
survive an attack by a rabid animal. Rabies may also present in a
so-called 'paralytic' form, rendering the infected animal unnaturally
quiet and withdrawn.
The virus is usually
present in the saliva of a symptomatic rabid animal; the route of
infection is nearly always by a bite. By causing the infected animal to
be exceptionally aggressive, the virus ensures its transmission to the
After a typical human
infection by animal bite, the virus directly or indirectly enters the peripheral
nervous system. It then travels along the nerves towards the central
nervous system. During this phase, the virus cannot be easily detected
within the host, and vaccination may still confer cell-mediated
immunity to pre-empt symptomatic rabies. Once the virus reaches the
brain, it rapidly causes an encephalitis and symptoms appear. It may
also inflame the spinal cord producing myelitis.
The period between
infection and the first flu-like symptoms is normally 3-12 weeks, but
can be as long as two years. Soon after, the symptoms expand to
cerebral dysfunction, anxiety, confusion, and agitation, progressing to
delirium, abnormal behavior, hallucinations, and insomnia. The
production of large quantities of saliva and tears coupled with an
inability to speak or swallow are typical during the later stages of
the disease; this is known as "hydrophobia". Death almost
invariably results 2-10 days after the first symptoms; the handful of
people who are known to have survived the disease were all left with severe
A Lyssavirus causes
rabies. This group of RNA viruses includes the Rabies virus as well as
bat lyssaviruses Duvenhage viruses and others. Human-infecting viruses
may commonly have cubic symmetry and take shapes of regular polyhedra.
The Lyssaviruses are the
only viruses known to travel along the nerves after infection. Biopsy
shows typical "Negri bodies" in the infected neurons.
There is no known cure
for symptomatic rabies, but it can be prevented by vaccination, either
of humans or of animals. Rabies originally doomed almost everyone who
got it to die, until Louis Pasteur developed the first rabies
vaccination in 1886 and used it to save the life of Joseph Meister, who
had been bitten by a mad dog. Current vaccines are relatively painless
and are given in one's arm, like a flu or tetanus vaccine.
Treatment after exposure
(known as post-exposure prophylaxis or "PEP") is highly
successful in preventing the disease if administered promptly. In the
United States, the treatment consists of a regimen of one dose of
immunoglobulin and five doses of rabies vaccine over a 28-day period.
Rabies immunoglobulin and the first dose of rabies vaccine should be
given as soon as possible after exposure, with additional doses on days
3, 7, 14, and 28 after the first. In case of animal bites it is also
helpful to remove, by thorough washing, as much infectious material as
soon as possible.
PEP is possible in rabies
because the virus must travel from the site of infection through the
peripheral nervous system (nerves in the body) before infecting the
central nervous system (brain and spinal cord) and glands and causing
lethal damage. This travel along the nerves is usually slow enough that
vaccine and immunoglobulin can be administered to protect the brain and
glands from infection. The time of travel is dependent on how far the
infected area is from the brain by nerve: if bitten in the face, for
example, the time until the brain is infected is very short and PEP may
not be successful.
40,000 to 70,000 people
die annually from rabies, mostly in Africa and Asia, where rabies is
endemic. About 10 million people receive treatment annually after
suspected exposure to rabies.
destruction of stray dogs, muzzling and other measures contributed to
the eradication of rabies from Great Britain in the early 20th century.
More recently, large-scale vaccination of cats, dogs and ferrets has
been successful in combating rabies in some developed countries.
Rabies virus survives in
widespread, varied, rural wildlife reservoirs. Mandatory vaccination of
animals is less effective in rural areas. Especially in developing
countries, animals may not be privately owned and their destruction may
be unacceptable. Oral vaccines can be safely distributed in baits, and
this has successfully impacted rabies in rural areas of France,
Ontario, Texas, Florida and elsewhere. Vaccination campaigns may be
expensive, and a cost-benefit analysis can lead those responsible to opt
for policies of containment rather than elimination of the disease.
Since the development of
effective human vaccines and immunoglobulin treatments the US death
rate from rabies has dropped from 100 or more per year early in the
20th century, to 1-2 per year, mostly caused by bat bites, which may go
unnoticed by the patient.
Australia is one of the
few parts of the world where rabies has never been introduced. However,
the Australian Bat Lyssavirus occurs naturally in both insectivorous
and fruit eating bats (flying foxes) from most mainland states.
Scientists believe it is present in bat populations throughout the
range of flying foxes in Australia.
Many territories, such as
the United Kingdom, Ireland and Guam, are free of rabies (although
there may be a very low prevalence of rabies among bats in the UK; see
Transport of pet animals between
Rabies is endemic to many
parts of the world, and one of the reasons given for quarantine periods
in international animal transport has been to try to keep the disease
out of uninfected regions. However, most developed countries, pioneered
by Sweden, now allow unencumbered travel between their territories for
pet animals that have demonstrated an adequate immune response to
Such countries may limit
movement of animals from countries where rabies is considered to be
under control in pet animals. There are various lists of such
countries. The European Union has a harmonized list.