RABIES AND ANIMAL BITES

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Although human rabies is quite rare in Indiana (last case in 1959), it nevertheless is of great public health interest. Out of 2,151 animals tested in 1996 by the ISDH Disease Control Laboratory, 9 were rabies-positive. The most commonly tested species included dogs (750), cats (722), bats (204), and raccoons (169). Eight of the rabies-positive animals were bats, and one was a skunk. The counties of origin are shown in Rabies-1.

Rabies-1

The year 1996 had the lowest number of animal rabies diagnoses in one year since at least 1962 (Rabies-2).

Historically, the skunk has been the major terrestrial (non-bat) rabies reservoir in Indiana. Since 1962, approximately 57% (815/1420) of the animal rabies cases have been in this species. Skunk rabies activity tends to fluctuate in Indiana in 6 to 8-year cycles. However, since 1990, there has been only 1 rabid skunk diagnosed in Indiana. Skunk rabies remains a problem in surrounding states.

From 1962 to 1996, approximately 22% of the animal rabies cases in Indiana have been in bats (Rabies-3).

The number of rabid bats diagnosed in Indiana also undergoes cyclic fluctuations (Rabies-4). Eight bat rabies ecotypes (strains) have been identified in the United States. Six of these are known to be circulating in Indiana. Nationally, almost all of the human rabies deaths in the last several years have been caused by one of the bat ecotypes. Often the victim had no known bat bite and in some cases no known bat contact. Thus, any contact or potential contact with an untested bat should be evaluated very carefully.

The number of rabid cats and dogs has declined markedly in the past 25 years (Rabies-5). The last rabid dog and cat in Indiana were diagnosed in 1989 and 1984, respectively. Domestic animals in Indiana become infected primarily through exposure to rabid wildlife. Therefore, both dogs and cats should be vaccinated against rabies, as required by state law. Immunization of farm species is not indicated at present in Indiana.

Raccoon-strain rabies virus has entered Ohio's eastern counties. There is no reason to expect that it will not eventually reach Indiana. When it does, the experience of East Coast states suggests that rabies-related activities will increase dramatically. In raccoon-rabies endemic areas, the incidence of rabies in all species (except humans so far) increases. Thus, the dog bite that today would be classified as very low rabies risk will become much more likely to require post-exposure prophylaxis (PEP) under raccoon-strain endemic conditions. In fact, human PEPs increase about 5 fold after raccoon-strain rabies becomes established.

The best way to prevent rabies is to avoid exposure to potentially rabid animals. Don't keep wild animals as pets, and don't feed or attempt to touch free-living wild animals. Keep pet food away from wild animals, and secure garbage can lids. Vaccinate all dogs and cats.

See Appendix B for a discussion of bat-strain and raccoon-strain rabies virus, PEP, and the risks posed by bites from various species of animals.

Cases = 6,695

Crude incidence = 121/100,000

A total of 6,695 animal bites, an approximately 20.7% decrease over 1995 (8,438), was reported in Indiana in 1996, for an incidence rate of 152 bites per 100,000 population. 2052 animal bites were reported from Marion County in 1996, accounting for almost 31% of the state total and yielding an incidence rate of 257 per 100,000 population. The number of bites reported from areas outside Marion County may be lower in 1996 because the animal bite data base was moved to a new computer and ISDH moved to a new facility during 1996. Data may have been lost in the process. Because animal bites are frequently under-reported, the figures presented here should be considered minimums.

The dog is still the most common biting animal, accounting for about 80% (5398/6695) of the incidents, followed by the cat at almost 15% of the state-wide total (987/6695). Twenty four bat bites were reported in 1996. This species is currently the most important rabies reservoir in the state. These data are summarized in the pie chart on the next page.

Dog bites accounted for about 78% of the 23,772 reported animal bites during this time period. Cat bites comprised 16% of the reports.

Of the rodent bites, those inflicted by mice and rats were most common, followed by squirrels. Of the wild mammals, bites inflicted by raccoons were most common, followed by bats, foxes, and skunks.

Children in the 5-9 year age group had the highest incidence of bites, followed by children aged 10-14. The incidence in boys was higher than that of girls, however this sex difference was not significant in adults

The incidence of bites was highest in all age groups of children during the months of April-June followed by July-September.

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