Disease
Rabies is an acute encephalitis (infection of the brain) caused by a virus believed to be infectious for most mammals. Transmission of the virus is usually through a bite. Transmission also can occur by exposure of a scratch, abrasion, open wound or mucous membrane to saliva or brain material of a rabid animal. The virus has an affinity for the central nervous system tissue and travels along the peripheral nerves to the brain. Once the virus is established in the brain the disease is seldom reversible and usually fatal. The average incubation period varies from 20-90 days after exposure and depends on the following circumstances: a) severity of bite or laceration, b) location of bite (incubation periods may be shorter after bites on head, neck, and fingertips, than bites on the trunk or lower extremities due to extensive nerve endings in the former areas), c) age of the victim (children have faster onset). Two clinical patterns may be manifest and are referred to as "dumb" or paralytic rabies and furious rabies (prone to bite).

Epidemiology
Rabies is endemic in several wildlife populations throughout specific geographical areas. These animals act as the reservoir for the rabies virus and for its continued spread. The raccoon appears to be the natural reservoir in the south and southeast U.S., the fox and bat throughout the U.S., and the skunk in the Mississippi River basin and plains area. There are two primary forms of rabies: urban rabies, spread by nonimmunized domestic dogs and cats and rural rabies spread by the skunk, fox, raccoon, bat, and occasionally livestock. In the midwestern states there is a high incidence of cow rabies from exposure to skunks.

The skunk is the most common source of exposure followed by cows in the state of Iowa. Rabies is not endemic in either wild or domestic rodents (rats, mice, hamsters, guinea pigs, squirrels), insectivores (moles, shrews) or lagomorphs (rabbits, hares). A bite from any of these animals has never been linked to a case of human rabies in the U.S. and antirabies prophylaxis is almost never indicated following exposure to these animals.

Prevention
Mass vaccination of domestic pets and control of strays has markedly reduced urban rabies. Even though the numbers of positive rabies cases are fewer in domestic animals than in wild animals, dogs, cats, and farm animals continue to present a substantial risk to humans. Their close contact with humans introduces the risk when rabies immunizations are not kept current. This is especially true in the rural settings where it is not economically feasible or justified to vaccinate livestock. Owners of valuable animals and breeding stock should consider vaccination especially in areas of high wildlife rabies.

Making pets of wildlife or exotic animals should be discouraged since many could be infected with the rabies virus. High risk individuals such as veterinarians, animal handlers, laboratory workers, people with occupational or avocational risk (trappers, taxidermists) and individuals living and working in a country where rabies is a constant threat should consider pre-exposure immunization.

Vaccines are specific for each animal. Immunization is limited by techniques and tolerances, hence should be administered by a veterinarian. Table 1 gives an abbreviated vaccine schedule for animals. Human immunization must be administered by a physician.

Exposure and Treatment
Each exposure to a possible rabies infection must be individually evaluated by a physician and the following circumstances considered:

1. Animal species
1. Wild or domestic species (vaccination history)
2. Carnivore or rodent
2. Circumstances surrounding the bite
1. Unprovoked attack is more likely to indicate that the animal is rabid
2. Provoked bites are inflicted on a person attempting to feed or handle a healthy animal
3. Petting a rabid animal or other casual contact does not constitute an exposure and is not an indication for prophylaxis.

Collection and Shipment
When the decision is made to examine an animal for rabies, then follow the proper procedures for submission of the specimen to a laboratory. Ship the animal head in a sealed container along with a refrigerant (freezer packs). Hand deliver or use a one-day delivery service courier. A history which includes species of animal, immunization record, nature of human or animal exposure, names and addresses of owner and persons bitten and a physician or veterinarian to send the report. For information about rabies and for submission of specimens contact the following: