Rabies

Rabies, or rage, is a viral disease that causes acute encephalitis in animals and people. It can affect most species of warm-blooded animal, but is rare among non-carnivores. 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. Rabies may also present in a so-called 'paralytic' form, rendering the infected animal unnaturally quiet and withdrawn.

In humans, untreated rabies is almost invariably fatal. Between 40,000 and 70,000 die annually from rabies, most in Africa and Asia where rabies is endemic. About 10 million people receive treatment annually after suspected exposure to rabies. [1]

Rabies is caused by a 'Lyssavirus'. This group of viruses includes the Rabies virus traditionally associated with the disease, Australian bat lyssavirus, Duvenhage virus, two European bat lyssaviruses, Lagos bat virus and Mokola virus. Viruses typically have either helical or cubic symmetry. Lyssaviruses have helical symmetry, so their infectious particles are approximately cylindrical in shape. This is typical of plant-infecting viruses. Human-infecting viruses more commonly have cubic symmetry and take shapes approximating regular polyhedra.

Transmission and symptoms

The virus is usually present in the saliva of a symptomatic rabid animal; the route of infection is nearly always via a bite. By causing the infected animal to be exceptionally aggressive, the virus ensures its transmission to the next host. In vitro transmission has occurred via an aerosol through mucous membranes; transmission in this form this may have happened in people exploring caves populated by rabid bats. Transmission from person to person has not been observed, except during corneal transplant surgery.

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 can be as long as two years, but it is normally 3-12 weeks. Soon after, the symptoms expand to cerebral dysfunction, anxiety, confusion, agitation, progressing to delirium, abnormal behaviour, 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 brain damage.

Prevention

There is no known cure for rabies, but it can be prevented by vaccination. 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 Joey Meister, who had been bitten by a mad dog. Current vaccines are relatively painless and are given in your arm, like a flu or tetanus vaccine.

Treatment after exposure (known as postexposure 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 bite it is also helpful to remove, by thorough washing, as much infective material as soon as possible.

Prevalence

Dog licensing, 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 combatting 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.

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 it out of uninfected regions. However, developed countries, pioneered by Sweden, now allow unencumbered travel between their territories for pet animals that have demonstrated an adequate immune response to rabies vaccination.

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.

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.

Great Britain, which has stringent regulations on the importation of animals, had also been believed to be entirely free from rabies until 1996 when a single Daubenton's bat was found to be infected with a rabies-like virus usually found only in bats - European Bat Lyssavirus 2 (EBL2). There were no more known cases until September 2002 when another Daubenton's bat tested positive for EBL2 in Lancashire. A bat conservationist who was bitten by the infected bat received post exposure treatment and did not develop rabies.

Then in November 2002 David McRae, a bat conservationist from Guthrie, Angus who was believed to have been bitten by a bat, became the first person to contract rabies in Great Britain since 1902. He died from the disease on November 24 2002.

External link

• http://www.cdc.gov/ncidod/dvrd/rabies/