Rabies is a serious disease caused by a rhabdovirus. It is one of the most feared infections of all time. Rabies was first discovered in the 16th century to be fatal by Girolamo Fracastoroand and in 1885 Louis Pasteur created the first vaccination. Despite today’s modern vaccination programs, the virus is still a threat to a significant number of human and mammal lives every year. Rabies is particularly dangerous because all warm-blooded mammals are susceptible. It is considered a zoonotic disease, one which is transmitted from animals to humans. Vaccinating against Rabies has helped to diminish the number of cases annually, but rabies still exists even in developed countries and runs rampant through Third World countries in Asia. The only places around the world that remain untouched by the virus are Australia, the British Isles, Cyprus, Hawaii, Japan, New Zealand, and Scandinavia.
Rabies remains a threat due to its high prevalence among unvaccinated wild animals. Species likely to carry the virus vary widely depending upon geographic location, but in the United States they include raccoons, skunks, bats, foxes, and coyotes. Highly susceptible animals in other parts of the world include wolves, mongooses, and jackals.
The most common way in which domesticated animals become infected with the rabies virus is via a bite. Transmission has also occurred via ingestion of infected tissue or by aerosol exposure, but bites remain by far the most prevalent mode of infection. Once an animal is bitten and infected the virus will multiply in the muscular tissue at the point of entry and will then travel to local nerves and finish its journey to the spinal cord and brain and where it incubates. Two days after it first arrives in the central nervous system, the virus is present in all body secretions and the virus is fully contagious. The amount of time that passes between initial infection and onset of clinical symptoms is highly variable. It was found that bites closer to the brain will lead to a shorter incubation period. Appearance of disease symptoms after initial infection may take anywhere from a few weeks to several months, but once they have appeared there is no cure for the disease.
There is no definitive set of clinical symptoms for rabies. Certain symptoms are however associated almost exclusively with the disease. There are typically three stages of a rabies infection, prodromal, furious, and paralytic (dumb). There is a high level of variation with the diseases progression and every case is unique so no case of rabies is ever the same.
In the first stage, prodromal, the animal will often exhibit vague, nonspecific symptoms. Signs include apprehension, restlessness, loss of appetite, temperament changes and sometimes vomiting. Symptoms will persist for 2 to 5 days. This stage is followed by either the paralytic or furious form of the disease.
About 30 percent of infected animals will progress from the prodromal stage to the furious form. It is more common in cats than in dogs and generally lasts 2 to 4 days. Symptoms of this phase are characterized by an increased level of restlessness, wandering, viciousness, howling, panting, drooling, and occasionally convulsions. Affected animals will often attempt to attack objects that may or may not be real.
The remaining 70 percent of infected animals will progress to the paralytic form of rabies, which also lasts between 2 and 4 days. This form is most common in dogs. Symptoms include ascending paralysis, beginning near the bite site and gradually progressing up the body, paralysis of the lower jaw, and facial paralysis. Biting is uncommon with this form, but excessive drooling does occur. Victims have difficulty eating and drinking. In dogs, a noticeable change in how the bark sounds occurs as the larynx becomes paralyzed. Symptoms progress to coma and death from respiratory paralysis.
Animals infected will die within 10 days after onset of clinical signs. Once clinical symptoms have appeared, there is no treatment. Any animal that has been exposed to rabies and is not properly immunized should be euthanized. If a vaccinated animal is exposed to the virus he should be re-immunized and kept under close observation for at least 3 months. Of course, if you ever suspect that your pet has been exposed to rabies, contact your veterinarian immediately.
– Meghan, Veterinary Technician
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