Rhabdoviruses are rod- or bullet-shaped enveloped viruses with a single strand minus-sense RNA genome. The significant members are rabies virus and a well-characterized laboratory strain Vesicular Stomatitis virus.
Epidemiology Rabies is distributed in most of the world except Australia and Antartica. The epidemiology reflects that of animals in the community. Where canine rabies remains common, most cases of human rabies come from dog bites. In locations where dogs are vaccinated, most cases of rabies come from exposure to rabid wild animals. In 1992 there were 36,000 cases of rabies globally. In the U.S., there have been very few human cases of rabies. However, there were 20,000 cases of racoon rabies in the eastern U.S., in addition to cases from coyotes and bats. Prophylaxis, which is vaccination of domestic animals, has reduced incidence of rabies.
Pathogenesis Following introduction through a break in skin, mucosal surfaces, or respiratory tract, rabies virus replicates in muscle cells and then spreads to neurons of PNS and CNS. It produces severe, oftentimes fatal, CNS disfunction.
Clinical Manifestations The viral inoculum plays an important role in rate of clinical disease. A bite on exposed skin is much more likely to cause infection than a bite through thick clothing. Mutliple bites are more likely to result in infection than a single bite. The incubation period varies from a few days to over 19 years, although most (75%) of pateints become ill within 90 days of exposure. Initial symptoms are associated with other systemic viral infections, such as fever, headache, malaise, and disorders of upper repiratory and gastrointestinal tract. Neurologic complaints during this period include subtle changes in personality and cognition as well as pain at the exposure site.
Human rabies infections are divided into 2 forms: furious and paralytic.
Diagnosis Diagnosis is simple. If somebody has suffered a bite from a rabid animal and exhibits hydrophobia, then they have rabies.
Treatment The wound should be washed thoroughly with 20% soap solution to strip the viral envelope. A healthy dog or cat is observed for 10 days. If behavior is normal, the patient needs only wound care. If the animal exhibits symptoms of rabies, it is tested for rabies virus infection. Rabies immunoglobulin is injected equally into both the gluteus maximus and the would area itself.