by Robert Teclaw, D.V.M, Ph.D.

Only 13 animals, 9 bats and 4 skunks, out of 2,103 animals tested in Indiana were rabies positive in 1996. Despite the relatively low number of cases, rabies remains an important public health concern in the state.

On average, about 20 people are reported to have been bitten by an animal each day in Indiana. The actual number of bite victims is no doubt much higher. For each of these bites, a decision must be made regarding post-exposure rabies prophylaxis (PEP). Some decisions are easy. If the biting animal is a dog or cat available for observation, a 10-day disease-free confinement period signifies that the animal was not shedding rabies virus at the time of the bite, and thus, PEP is not needed. (Many people forget that the 10-day observation period applies only to dogs, cats, and ferrets. There is no observation period for any other species.) Another option for biting dogs, cats, and ferrets is to humanely kill them and test their brains for rabies. This is often the option chosen when the biting animal is a stray, was acting strangely, or had a history of biting humans.

It is also easy to decide whether PEP should be given when the biting animal is a wild carnivore (fox, skunk, raccoon, coyote, etc.). If the animal is available for testing, the results of the test will indicate whether PEP is necessary. If the animal is not available for testing, PEP is always recommended. Except for special circumstances, such as when an animal exhibits unusual behavior, PEP is almost never indicated for rodent (e.g., mouse, rat, squirrel, hamster), guinea pig, or rabbit bites. Administration of PEP after the bites of other domestic animals, ground hogs, and other species should be determined through consultation with the victim, the victim's physician, the local health department, and if necessary, the Indiana State Department of Health.

The only important rabies vector not mentioned above is the bat. In the last few years, almost all of the rabid animals diagnosed in Indiana were bats. If a bat exposes a person, and the bat is available for testing, a PEP decision can await the results of the test. If the bat is not available for testing, PEP should be given immediately.

The criteria for determining bat exposure changed at the beginning of 1995 due to a disturbing trend in the exposure histories of new human cases. Of 21 indigenous human rabies cases in the United States since 1980, 18 were due to the bat strain of the virus. (Laboratory techniques are available to type the various strains of rabies virus. Strains are usually named after the species from which they are most frequently associated; e.g., bat, skunk, raccoon, etc. (There may be more than one strain associated with a given species.) Only one of the victims had a definite history of bat bite. Several others had been in the presence of bats, but no known contact was made. Thus, it appears that it is possible to be infected with bat-strain rabies without being bitten and/or by being bitten, but not realizing it. In either case, the previous recommendation that PEP was needed only if a bat bite or contact with bat saliva occurred had to be changed. Now PEP is recommended when someone has been in the presence of a bat and contact cannot be ruled out. Some situations in which this might occur include finding a bat in a room with the following: an infant or young child, a person sleeping, someone heavily sedated by alcohol or other drug, or a person with diminished mental capacity.

One other development will have a dramatic effect on rabies activities in Indiana. In the late 1970s, raccoons were translocated from the southeastern U.S. to the West Virginia-Maryland border area. At least one of the raccoons was infected with raccoon-strain rabies virus, a type not previously known to occur that far north. Since that time, the raccoon-strain virus spread from the original focus, and now, raccoon populations in essentially all of the East Coast of the U.S. are infected. The virus moved rapidly north, south, and east, but westward, spread was much slower. Several hypotheses have been advanced to explain the slow, westward movement, but the most likely is that the Appalachian Mountains presented a physical and biological barrier. Raccoons, and thus the rabies virus, moved readily along the north-south valleys, but crossing the mountains, with their lack of water courses and low raccoon population densities, impeded spread.

Essentially, all of Pennsylvania's counties have recorded infections with raccoon-strain rabies virus. Until recently, Ohio was believed free of that strain. In 1992, a raccoon was found infected with raccoon-strain rabies virus just inside Ohio's border with Pennsylvania. That raccoon was believed to have originated in Pennsylvania. In early 1996, a cat with raccoon-strain rabies was diagnosed in Ohio. The cat was a gift from a Pennsylvania resident, and had been living in Ohio less than 30 days at the time of diagnosis. Finally, in late spring of 1996, a raccoon-strain rabid raccoon was found about 4 miles west of the Pennsylvania state line. Additional incursions by the raccoon-strain virus can be expected in the future, and sooner or later, the virus can be expected to arrive in Indiana.

Once the raccoon-strain rabies virus reaches Indiana, all rabies activities in the state will experience a significant increase. Probably the most important change will be the number of people receiving PEP. Currently, Indiana has very little rabies in terrestrial animals. The last rabid dog and cat were diagnosed in the state in 1989 and 1984, respectively. Now, when a dog or cat bite occurs, we know that the risk of rabies is extremely low. So even if the animal is not available for observation or testing, PEP often is not administered. Given the experience of the states to the east, though, the arrival of raccoon-strain rabies will increase the rabies risk of dog and cat bites, and therefore, will result in a significant increase in PEP.

What can we do to prepare for the arrival of raccoon-strain rabies? Since humans become exposed to wildlife rabies (except bats) primarily through pets, the single most important preventive step is to make sure that all dogs and cats in the state are vaccinated. Another way to reduce the risk of exposure is to remove sources of food that lure raccoons into close proximity to humans. Garbage cans should be raccoon proof, and pet food should not be left out overnight where raccoons have access to it. Finally, it is never wise to feed or handle wild animals; they should be enjoyed from a distance. An oral rabies vaccine is available for raccoons, but the field test results so far have been mixed. An oral-baiting campaign would not be practical; however, as a long-term solution. The only good news is that in spite of literally tens of thousands of raccoon-strain rabid animals diagnosed on the East Coast in the last 15 years, no humans have become infected with this strain. This has been the result of vigorous education programs and as much as a ten-fold increase in the use of PEP. Several agencies and organizations in Indiana are taking the first steps to plan for raccoon-strain rabies. We hope it does not arrive, but if and when it does, we will be ready.