Rabies exists on all continents except Australia and Antarctica. It is a disease primarily of bats and carnivores, including the domestic dog and cat. It has been a recognized disease of dogs and other animals since before the dawn of recorded history. Vaccination programs aimed at domestic dog and cat populations has virtually eliminated human cases of rabies.
Rabies virus cycles in nature through wild and domestic carnivores and through certain other wildlife species. In the United States, skunks play a major role in transmitting the disease, especially in the Midwest. In the southeastern states, raccoons are the primary reservoir. The primary mechanism by which the virus is transmitted is by the bite of an infected animal.
The incubation period for rabies can be quite variable, ranging from a week to as long as a year. This variability reflects the amount of time the rabies virus is retained in the muscle cells at the site of inoculation, usually a bite wound. Following the early stage of infection, the virus crosses the connections between the muscle cells and adjacent nerve cells and advances into the nervous system until it gains access to the spinal cord and eventually the brain. Invasion of the brain is followed by virus spread to additional sites important for subsequent transmission of the virus, such as the salivary glands, respiratory system and digestive tract. Salivary shedding of virus in dogs can begin as much as one or two weeks before the actual onset of clinical symptoms. Once clinical symptoms are exhibited, the outcome is inevitably fatal.
In general, there are two manifestations of rabies: the excitatory or furious form (the more well known and more graphic), and the paralytic form. In actuality, most cases of rabies exhibit one or more manifestations of both forms. The paralytic form always represents the terminal stage of the disease; however, some animals die during convulsive seizures while in the excitatory stage.
In dogs, the excitatory stage of rabies may last anywhere from 1 to 7 days. It is characterized by restlessness, nervousness and a developing viciousness. Affected dogs may snap at imaginary objects and try to bite any animal or human that approaches. Initially this behavior is directed toward strangers, but as the disease progresses a dog may turn on its owner. Excitability, a heightened sensitivity to being touched, and a hypersensitivity to light (photophobia) may also be present. If restrained, a rabid dog may chew viciously on its leash or on the bars of its cage. It may break its teeth, lacerate its mouth and gums, and drool a ropy slobber tinged with blood and teeming with rabies virus particles. A heavy, rapid respiration through the mouth may cause frothing of the saliva - providing the classic, characteristic picture of the rabid dog.
Affected dogs frequently appear oblivious to pain or other discomfort. They may utter weird, howling cries or hoarse yowls because of the advancing paralysis of the muscles of the voice box (larynx). An aversion to water (hydrophobia) seems to occur only rarely in canine rabies. Instead, there is a growing loss of interest in food. Sometimes affected dogs will attack and swallow strange objects, such as wooden sticks, pebbles, gravel or fecal material. An advancing facial paralysis may prevent the dog from closing its eyes. The corneas then become dry and dull, and the pupils may dilate widely, producing a characteristic staring or "faraway" look.
Within a very short time signs of excitement (when they occur) give way to the final, paralytic stage of the disease, which typically lasts for a day or two. The paralytic stage may be difficult to diagnose when it represents the sole clinical manifestation of the disease. The paralysis usually appears initially in the muscles of the head and neck, the most characteristic sign being difficulty swallowing. An affected dog cannot chew or swallow its food or does so only with great difficulty. Localized paralysis is followed quickly by more generalized paralysis, with coma and death following shortly thereafter.
For both dogs and humans, rabies is an inevitably fatal disease once clinical symptoms have appeared.
Utmost caution must be observed if one suspects that a pet has been exposed to rabies virus.
Owing to the potential risk of exposing human beings to rabies virus, attempted treatment of animals suspected of having rabies is not recommended. Treatment of human beings exposed to a known or suspected rabid animal, however, must be aggressively applied. Any person bitten by a wild animal should immediately report the incident to his or her physician, who can evaluate the need for anitrabies therapy. Treatment should consist of flushing and cleansing of the bite wound with soap and water (the importance of this simple measure cannot be overemphasized); administration of rabies virus antiserum to exposed individuals who have no previous history of rabies virus immunization; and administration of diploid-cell rabies vaccine.
Vaccinate your dog!