Legend: Electron micrograph of rabies virus in brain cells at 64,000x magnification. The bullets surrounding the smoothe gray circle are rabies. The circle itself is the negri body, which can be seen with a light microscope. Courtesy of Dr. F.A. Murphy, UC Davis.
The virus initially replicates in the muscle cells or cells of the subepithelial tissue. Then when its concentration is sufficient to infect the motor and sensory nerves in the muscle or skin it binds the the acetylcholine receptors or other receptors entering the nerve endings. The virus is then delivered to the central nervous system via axons in the spinal cord.
The infected individual may experience two forms of the virus depending on the location of neuronal infection. Furious Rabies is exhibited when the virus replicates in the limbic system while Dumb Rabies is experienced when the virus replicates in the neocortex.
Dumb Rabies manifests itself in the opposite manner as Furious Rabies . Instead of demonstrating excitement the patient experiences depression and paralysis followed by a coma. Death eventually results from respiratory arrest. This form of the virus is often difficult to diagnose from a clinical perspective.
The measures used by different geographic regions varies and is determined by whether the area is free of the disease, if the country is industrialized or developing and the incidence of bat rabies in the area.
Rabies free countries are maintained by enforcing strict quarantine regulations of dogs and cats for 6 months. In developing countries, where rabies is a serious problem, large doses of human vaccines are administered. In addition, stray domestic animals are strictly monitored, dogs and cats are immunized to break the chain of viral transmission and public education programs are promoted.
In industrialized countries the control of rabies in wildlife is generally based on the animal population. The immunization of wildlife species has shown to decrease the prevalence of rabies in Switzerland and Germany. The administration of more wildlife vaccinations will be determined by the population density of the target species, research analyzing the efficacy of orally ingested wildlife vaccines as well as the appropriate delivery system for each reservoir.
Bat rabies has been a problem in humans and livestock in several countries of Latin America. Bovine vaccines and anticoagulants have been administered to solve the problem. These drugs cause the rabid bats to suffer fatal hemorrhages in their wing capillaries when they feed off the blood of the treated cattle.
Rabies is the only human disease that can be treated by a postexposure vaccination. This form of treatment is can be utilized because the time of infection is generally known by the victim and the incubation period for the disease is long. The vaccines utilized are live attenuated vaccines. People at risk for acquiring rabies should be immunized with a vaccination and also be administered rabies immune globulin intramuscularly and around the bite. If the vaccine and the immune globulin is administered promptly after infection the mortality of the disease will be decreased from 100% to zero. Individuals catagorized as "high risk" for rabies include laboratory personnel working with the rabies virus, veterinarians, animal control and wildlife workers and travelers visiting areas where rabies is known to exist.
The vesicular stomatitis virus is a member of
the rhabdovirus family. It
is a zoonotic virus and is transmissible to humans from the vesicular
fluids and tissues of infected animals. Veternarians and farmers are at
the greatest risk. There is no practical way to prevent occupational
exposure. The disease resembles influenza and resolves without
complications within 7-10 days. VSV has been used to elucidate the
process of protein targeting.
Useful web links
The Humans and Viruses Course Reader
Human Biology 115A
Robert Siegel M.D. PhD.
Created: February 1, 1998
Last modified: March 3,1998