A Long Quiet Wait
Rabies is a viral disease spread mainly through the bite of an infected animal. What makes it unusual is its timing: the gap between infection and the first symptoms is typically one to three months in humans.
The early signs give almost nothing away. They are nonspecific, usually fever and headache, and could belong to any number of illnesses.
Then the virus reaches the brain. As it causes inflammation there, symptoms include partial paralysis, anxiety, insomnia, confusion, agitation and hallucinations, progressing to delirium and coma. Death usually follows two to ten days after symptoms first appear.
That progression is effectively one-way. Once symptoms have presented, survival is almost unknown even with intensive care.
About 80 percent of cases take the form historically called hydrophobia, or fear of water, because swallowing becomes difficult and painful and patients come to dread drinking. The remaining fifth take a paralytic form marked by weakness and loss of sensation, without the fear of water.
Why the Virus Makes Animals Bite
The disease's behaviour makes grim sense from the virus's point of view.
In the common form, infection produces irrational aggression in the host, which directly helps spread the virus, since transmission happens through bites. At the same time the virus multiplies and accumulates in the salivary glands, and the animal cannot swallow its own saliva. The result is exactly what most people picture when they think of rabies.
Humans have known about this for a very long time. The first written record is in the Mesopotamian Codex of Eshnunna from around 1930 BC, which required the owner of a dog showing symptoms to take precautions against bites, and imposed a heavy fine if someone was bitten and later died.
Ancient remedies were useless and inventive. One physician prescribed a poultice of cloth and hyena skin, another a preparation made from a skull. In some cases the attachment under the tongue was cut out, because rabies was thought to originate there.
Pasteur's Vaccine
Almost all human exposure to rabies was fatal until 1885, when Louis Pasteur and Emile Roux developed a vaccine.
Their method was crude by modern standards. The virus was harvested from infected rabbits and weakened by letting the nerve tissue dry for five to ten days. Vaccines derived from nerve tissue are still used in some countries because they cost far less than modern alternatives.
Better versions followed. A human diploid cell vaccine was introduced in 1967, and cheaper purified chicken embryo and vero cell vaccines are now available. Because the virus takes weeks to reach the brain, treatment given after a bite can still work, which is why washing a bite thoroughly and seeking care immediately matters so much.
Animal vaccination does most of the work. Deaths in the United States fell from 100 or more a year in the early 20th century to one or two, largely through vaccinating dogs and cats. Most remaining deaths come from bat bites, which may go unnoticed and therefore untreated.
Baiting the Wild
Vaccinating pets is straightforward where pets are kept privately. In rural areas of developing countries it is much harder, since animals may not belong to anyone and destroying them is often unacceptable.
The solution is to vaccinate wildlife by feeding it. Oral vaccines can be distributed safely in baits, and the approach has cut rabies substantially in rural Canada, Europe and the United States. Ontario recorded a dramatic drop after an aerial bait campaign, and in Montreal baits are used on raccoons in a city park. Campaigns are expensive, but the cost-benefit analysis favours them.
Globally the disease is still a serious killer, and an avoidable one. An estimated 26,000 people died of rabies in 2010, down from 54,000 in 1990, with most deaths in Asia and Africa. Dogs remain the principal host across much of Asia, Africa and parts of the Americas.
A 2015 collaboration between international health and animal organisations set the goal of eliminating human deaths from rabies by 2030.
