What is it?
Rabies is a viral disease that causes acute inflammation of the brain. It is present in humans as well as other mammals, and it causes around 24 000 – 60 000 deaths per year, most of which occur in Asia and Africa.
Rabies is spread through the bite of an infected animal: in some parts of the world this is most often done by dogs, while elsewhere bats are common transmitters. Later, on average after 1-3 months after infection, early symptoms such as fever and tingling at the site of the bite begin. In about 80% of cases this is followed by uncontrollable excitement, violent movements and often fear of water. In 20% of cases the person experiences muscle weakness, loss of sensation, and paralysis instead. Only five people are known to have survived rabies after the onset of symptoms.
What causes it?
Rabies is caused by the infection of a virus. All warm-blood species can become infected with it. Since the virus is present in the saliva of an infected animal, transmission usually occurs through biting. Sometimes contact with eyes, the mouth or the nose can be enough.
What happens during it?
Viruses work by invading a cell and turning it into a virus factory. When the rabies viruses are first introduced to the body, they start replicating in the skin or muscle cells. Our brain sends messages through our spine to our muscles to get them to move, and these neural routes are also the pathways that the viruses use. They work their way up to the spinal cord and to the brain. Our body realizes that it has been invaded and starts an inflammation to support fighting back: during inflammation our blood vessels dilate to allow more white blood cells to come to the area, for example. This reaction might be beneficial to fighting microbes, but it certainly isn’t good for our brains. Most of the symptoms of rabies and the eventual death are caused by how harsh this all is to the central nervous system. Our brain controls all the important functions of our bodies, including breathing and the beating of our hearts, and when these vital mechanisms are disrupted, the person won’t last much longer.
Many associate rabies primarily with the fear of water and the excessive production of saliva. These symptoms occur because once the virus has invaded the brain, it moves to the salivary glands to replicate. The viruses have evolved to have the best chances of being transmitted to some other animal. They make the person very reluctant to swallow and maybe even panic with the sight of water, which combined with an increased saliva production makes the viruses stay in the mouth much longer and have a better chance of infecting others through bite.
How can it be treated?
Rabies can be prevented very effectively if it’s done before infection or between infection and showing symptoms. This can be done through vaccines. After the onset of symptoms treatment usually only focuses on alleviating pain, as there is very little hope of improvement. A small number of people have, however, survived using an experimental method. This method is based on the presumption that the fatality of rabies is caused by the momentary dysfunction of the brain and, if the patient is put into a coma to halt the brain functions, the body is with medical help able to fight the infection off.
Sources: http://virology-online.com/viruses/Rhabdoviruses3.htm, http://www.mass.gov/eea/agencies/agr/animal-health/rabies-control-program/pathogenesis-of-rabies-generic.html, http://www.nhs.uk/Conditions/Rabies/Pages/Introduction.aspx, https://en.wikipedia.org/wiki/Rabies#Treatment