Rabies is a rare, but usually fatal, contagious viral disease that is spread among warm-blooded animals, including humans. There have been less than 100 cases of rabies in the United States since 1990. This number is so low thanks to comprehensive vaccination programs. However, tens of thousands of people die of rabies each year in Asia and Africa, where the disease is not well controlled in animal populations. Bites from unvaccinated dogs cause most of these cases. Rabies is sometimes referred to as hydrophobia, due to the fear of water that develops in the disease’s later stages.
What is rabies?
The term is derived from the Latin rabies, “madness”. Rabies is caused by the lyssavirus (derived from the Greek word lyssa, “violent”) which belongs to the order Mononegavirales (viruses with a nonsegmented, negative-stranded RNA genomes) and is a member of the Rhabdoviridae family (animal viruses shaped like a bullet – rhabdos in Greek). It enters the body through a bite or scratch from an infected animal, as the saliva of infected animals usually has a large amount of the virus in it. Once inside the body, it finds the nearest nerve or muscle cell, where it begins to replicate itself. As it replicates itself, the virus works its way toward the central nervous system. Once it is there, symptoms of the disease begin to appear. Concentrations of the virus are deposited in different parts of the body on its journey to the central nervous system, with the salivary glands receiving the highest concentrations, making biting the most common form of virus transmission.
Where does rabies come from?
Rabies has been noted by humans for thousands of years because of its ability to make a victim violent. The first written record of rabies as a known disease is found in the Codex of Eshnunna from Mesopotamia in approximately 1930 B.C. This record instructed that owners of dogs that show symptoms of rabies should do what was necessary to prevent the dog from biting the owner or others; owners of rabid dogs who bit other people, causing those people to die, were to be given heavy fines. Rabies became very prevalent in 19th century Europe. Many people were infected by rabid dogs, and there was no effective treatment at the time. Sometimes people who were bitten by a dog who had no symptoms of rabies killed themselves or were murdered by mobs “just in case” the dog was rabid. While these were tragic circumstances for Europe, it provided Louis Pasteur the opportunity to test many post-exposure rabies treatments beginning in 1885. These experiments led to Pasteur inventing the first effective rabies vaccine.
How is rabies transmitted?
The means of transmission of the virus is almost always through an animal bite, due to the high concentrations of the rabies virus in the saliva glands of those who are infected. Sometimes, the virus can be transmitted by a scratch, if the claw or nail has the blood or saliva of the infected animal or human on it. Human-to-human bite transmission is possible, it is very rare; a few cases have been recorded through transplant surgery. Wild animals like skunks, raccoons or coyotes are the most frequent transmitters of the rabies virus to humans in the United States, while dogs are the most common transmitters in the rest of the world. Those who are infected are prone to violent behavior that includes biting and scratching, as the virus modifies the host’s behavior to facilitate transmission.
What are rabies symptoms?
There may be a significant time delay between being infected with the rabies virus and the onset of symptoms. The typical time period is one to three months, but can be as long as a few days to more than a year. It all depends on how far the virus has to travel to reach the host’s central nervous system. Incubation periods of as long as six years have been reported, but are rare. Once symptoms begin, the disease is almost always fatal. The flu-like symptoms of rabies include a fever and a tingling sensation at the site of the virus’s entry. This is followed by paralysis, anxiety, confusion, paranoia, terror, erratic movements, extreme excitement, violent behavior and hallucinations, progressing to delirium. Some people might experience hydrophobia. Rabies in humans almost invariably results in death 2 to 10 days after first symptoms.
What is the rabies vaccine?
Rabies can be prevented by vaccination, and can also be treated and cured with vaccination if the vaccine is given very soon after exposure and before the onset of symptoms. The ability to cure the disease through vaccination before symptoms begin makes the rabies vaccine different from most other vaccines which are used merely for prevention and not treatment of diseases. The rabies vaccine for humans is different than the one used to confer immunity upon animals. The human vaccine is an inactivated one that is made with a weakened form of the Pitman-Moore L503 strain of the rabies virus, and is administered via intramuscular injection. The vaccine can confer immunity to rabies for two to three years, and a booster shot after a year can confer immunity for 10 more years. Many people who work with animals or work in the wilderness have a high susceptibility to rabies exposure, and get the rabies shot before exposure occurs. However, the rabies shot, given in two doses, can also prevent rabies from developing after a person has been exposed to it. In this, it is 100 percent effective. The rabies vaccine cannot cause rabies.
What are the rabies vaccine side effects?
Side effects from the rabies vaccine are rare. However, as with any medication, they sometimes occur. When they do, the most common side effects of the rabies vaccine are: nausea, itching or redness at the site of the injection, stomach pain, headache, chills, fever, muscle aches, joint aches, bruising at the site of the injection, hives and diarrhea. Other nervous system disorders, such as Guillain Barré syndrome (GBS), have been reported after rabies vaccine, but this occurs so rarely that it is not known whether they are related to the vaccine
Who should not get the rabies vaccine?
Women who are pregnant should not get the rabies vaccine pre-exposure, as it has been shown to cause negative effects in developing fetuses in animals. Anyone who is sick with anything should consult with their doctor before taking any pre-exposure vaccine. However, once someone has been exposed to rabies, there is no choice but to take the rabies vaccine in order to prevent the disease from developing. Post-exposure vaccination for rabies (before symptoms appear) saves lives 100 percent of the time.
Sources:
http://www.cdc.gov/rabies/
http://www.cdc.gov/rabies/transmission/virus.html
http://www.cdc.gov/vaccines/hcp/vis/vis-statements/rabies.html
http://www.who.int/rabies/en/
