Vermont. May 1, 2011. When the raccoon showed up in the mid afternoon and did not seem to object to loud clapping to shoo it away the very first thought was rabid animal.
Rabies caused by the virus Rhabdoviridae lyssavirus is one of the oldest and most feared human diseases, rightfully so because rabies is 100% fatal to warm blooded mammals once it enters the nervous system. Although worldwide there are up to 50 thousand human deaths a year from rabies, it is a rare event in the US.
The rabies virus is microscopic, bullet shaped, conical at one end, flat at the other and like all viruses is balanced between life and not life.¬ Viruses cannot live outside host cells.¬ They must use the genetic material in living host cells to propagate themselves and in doing so destroy the living cell.¬
Once in the host the rabies virus will reproduce itself in certain muscle cells in the immediate area of a wound until the virus replicates sufficient numbers and reaches a nerve ending, infecting the nervous system.¬ The nervous system is isolated from our blood circulatory system so our usual first line of defense, blood born antibodies can offer no protection. Fortunately this delay in the spread of the virus to the nervous system is what that allows for treatment by vaccine.
The virus will replicate itself along the nerve path eventually reaching the spinal cord.¬ From here the virus attacks the limbic system, that part of the brain associated with basic emotions such as fear, hunger, pain, pleasure, satisfaction, sex, hence the furious nature of rabid animals.¬ From the limbic system the virus spreads back out to the body along the nerves including those that lead to the salivary glands.¬ Saliva transferred during bites provides the virus an ideal medium to pass from its dying host to a new host.
Rabies has existed for eons.¬ Ancient Babylonian records from 2300 BC recognized rabies as a disease transmitted from dogs to humans.¬ Worldwide tests of rabies virus taken from bats and foxes show that the viruses are similar everywhere. The conclusion is that the rabies virus has not changed dramatically over its 4000 years of human observation.
As humans expanded their territory they traveled with their household animals leading to epidemics of rabies in Europe in the 13th century. Canine rabies was unknown in Americas until the arrival of Europeans.¬ The Spanish brought dogs to South and Central America releasing the virus in the early 1500s. The first outbreak in America was recognized in Virginia in 1753.¬ By the 1870s rabies was prevalent in dogs in all urban centers east of the Mississippi River.
The earliest known treatment was to wash the wound well and cauterize the bite with a hot iron. Tests have proven that the rabies virus becomes unstable as temperature increases; dropping from a half-life of 24 hours at 40 degrees F to a half-life of 35 seconds at 140 F.¬ The virus’s sensitivity to temperature and initially staying close to the puncture point meant the treatment of a hot iron actually had value in preventing the disease.
In 1885 Louis Pasteur developed the first post exposure vaccine for rabies, albeit his live virus treatment was potentially life threatening itself. From the turn of the 20th century rabies vaccines have become safer and more effective with the first pre-exposure treatment developed in 1964 by combining the vaccine with blood serum. Pre and post exposure success rates have climbed dramatically since 1970s.
There are two traits that make the rabies virus a survivor despite killing its host.¬ In most cases the virus ¬can not be defeated by an immune host because the virus is not exposed to the immune system.¬ ¬ In addition the virus can sit dormant for extended periods of time in a new host, up to 15 months in foxes. This incubation period allows the virus to be transported long distances into new geographic areas where the virus finds new susceptible hosts. Complete eradication of rabies seems unlikely since throughout its existence ¬it has always had a repository of infected animals from which epidemics can strike certain species.
Raccoons and animals infected by raccoons now account for more than 60% of all cases of rabies. Pre-exposure vaccines make it possible to restrict large infections by baiting the outer fringes of the outbreak area anticipating the arrival of infected animals.¬ It works because the animals in the infected area die off leaving the virus with no living hosts but the virus cannot spread into the immune population.
In the end the rabies virus will survive in wild animal populations for the coming eons. If a wild animal acts strangely leave the area. Do not pick up dead animals without proper protection and if bitten immediately seek medical attention. Enjoy the out of doors but be smart and report any unusual animal sittings to your health department in VT at 1-800-472-2437 and in NH at (603) 271-4496.
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David Deen is River Steward for the Connecticut River Watershed Council. CRC has been a protector of the Connecticut River for more than half a century.