2000 Indiana Report of Infectious Diseases
Rabies and Animal Bites
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Rates presented are per 100,000 population and are based on the U.S. 2000 Census.
Rabies in Animals
Cases = 14 Bats
Currently, Indiana has two reservoirs of rabies virus, skunks and bats. During 1996-2000, bats have represented 90.2% of the animals found rabies positive by the Indiana State Department of Health Rabies Laboratory. Since 1990, bats have represented 94.8% of the rabid animals submitted to the ISDH Labs, with the only other rabies-positive animals being 6 skunks, 2 horses, and 1 fox.
In 2000 the ISDH Labs tested 2,093 animals for rabies. The most frequently tested animals were dogs (734), cats (654), bats (377), and raccoons (128). These species represented 78.5% of the animals submitted. The other 21.5% of animals were from 39 other species, with 1 to 20 animals per species submitted to the ISDH Labs for analysis. Counties of origin for bats identified as rabid in 2000 are shown in Figure Rab1.
The ISDH Labs identifies bats submitted by species. In 2000, the number and species of rabies-positive bats were 2 Eastern Pipistrelle, 6 Red, 1 Hoary, and 5 Big Brown bats.
The importance of rabies in bats must be examined in the context of a national perspective. In the U.S., since 1990, 32 human deaths have been attributed to rabies. Of the 32, 30 were due to a bat-variant virus or a foreign canine-variant virus. A bat-variant rabies virus caused 24 of the deaths. A history of bat bite was determined in 2 of the reported cases. In approximately 50% of the other cases, some contact with a bat occurred. Rabies is usually transmitted by a bite. Because a bat bite causes limited trauma, individuals may not have reported the bite or sought medical attention for such an exposure. In the U.S. in 2000, there were 5 human deaths from rabies, 4 from bat-variant rabies and one from an African-dog variant.
Due to the number of human rabies cases from bats without known bites, in 1999 the Advisory Committee on Immunization Practices made major changes in its recommendations for evaluating contact or potential contact with an untested bat. Current recommendation is that post-exposure prophylaxis (PEP) should be considered when direct contact between a human and a bat has occurred, unless the exposed person can be certain that a bite, scratch, or mucous membrane exposure did not occur. When a bat is found indoors, PEP can be considered for persons who were in the same room as the bat and who might be unaware that a bite or direct contact had occurred. For example, a sleeping person awakens to find a bat in the room or an adult witnesses a bat in the room with a previously unattended child, mentally disabled person, or intoxicated person and rabies cannot be ruled out by testing the bat. Seeing a bat or being in the vicinity of bats does not represent an exposure. Individuals bitten or scratched by any animal should wash wounds thoroughly and seek medical care for additional treated and PEP if indicated.
Cases = 8,957
Crude Incidence=147.3/100,000 population
In 2000, 8,957 animal bites were reported in Indiana, for a crude incidence rate of 147.3 per 100,000 population. Animal bites are frequently under-reported, especially minor bites that do not require medical attention for wound treatment. Therefore, the data presented here should be considered the minimum. Dogs continue to be the number one offender with 6,966 reported bites (77.7% of all bites), and cats the number two offender with 1,642 reported bites (18.3%). Reported bites from wild animals that are rabies reservoirs in Indiana or in other states were: raccoons, 43; bats, 37; skunks, 2; and foxes, 1. The balance of reported bites, 266, were from other domestic animals or wild animal species that are rarely or never reported as rabid.
Included in the 266 were 3 reported bites from monkeys. In addition to a risk assessment for rabies, monkeys should be identified by species. If the monkey is a member of the macaque family or housed with a member of the macaque family, it should be tested for herpes B virus. When transmitted to humans (approximately 40 known cases), the herpes B virus causes a rapidly ascending encephalomyelitis that is fatal in approximately 70% of the cases.
Age Distribution of Bite Victims
Children ages 15 or less are the most frequent victims of animal bites. Of the 7,936 reported animal bites where the victim's age was known, 39.8% were in those ages 15 or less, and 48% were in those ages less than 19. Figure Rab2 illustrates the disproportionately high rates in the younger age groups. The female to male ratio for victims of animal bites varies by age group, as well. For those ages 0-4, the female to male ratio is 1:1.04; 5-9, 1:1.31; 10-14, 1:1.65; and >15, 1:0.89.
Rabies Post-exposure Prophylaxis (PEP)
In 2000, circumstances of an animal bite or exposure resulted in a decision to administer post-exposure immunization against rabies in 66 cases. The PEP series consists of an initial dose of human rabies immune globulin and 5 doses of rabies vaccine given on day 0, 3, 7, 14, and 28. Figure Rab3 presents the number of PEP treatments required by species.
Animal Vaccination Status
Administering rabies vaccine to dogs and cats is the primary barrier to preventing human exposure to rabies regardless of the primary reservoir of rabies (domestic animals or terrestrial wildlife). For animal bite reports that included the rabies vaccination status (yes, no, unknown) of the biting animals, 50.4% of dogs (Figure Rab4) and 25.2% of cats (Figure Rab5) had a current rabies vaccination. Indiana State law requires annual rabies vaccination for dogs, cats, and ferrets.