1998 Rabies Annual Summary
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Director, Rabies Laboratory
Richard Raczkowski:
Asst. Director, Rabies Laboratory
518-869-4527
Please contact us (518-869-4527) for data tables and image maps in an alternate format.
- Introduction
- Specimens Tested
- Rabies in Domestic Animals
- Raccoon Rabies
- Bat Rabies
- Human Serological Testing
- 1998 Rabies Incidence Map (GIF 49k)
- 1998 Bat Rabies Map (GIF 73k)
- 1998 Raccoon Rabies Map (GIF 41k)
- Additional 1998 Graphical Rabies Data
Introduction
This was the eighth consecutive year in which there were more than one thousand laboratory- confirmed rabid animals in New York State. The raccoon-vectored outbreak that has affected the state since 1990 accounted for 90% of the cases, and yet, it was rabies in bats that resulted in record breaking numbers and the most perplexing public health issues.
Testing Results
There were 10,881 animals examined for rabies infection in the state during the year, a 5% increase over the 1997 figure. The Wadsworth Center rabies laboratory examined 9,866 and the New York City Health Department laboratory examined 1,015. Specimens included 57 different species of mammals, with samples originating from each of the state's 62 counties. The largest category of animals examined was bats, comprising 28.9% (3,141) of all specimens received. This was the greatest annual total of bats tested in the state, and represented an increase of 32.6% from the 1997 total and nearly twice the average for the previous five year period (1,631). The laboratories also examined 2,283 domestic cats which comprised 21.0% of all animals tested, as well as 2,180 raccoons (20%), 961 dogs (8.8%), 696 skunks (6.4%), 626 rodents (5.8%), 224 foxes (2.1%), 169 cattle (1.6%), 468 other wild (4.3%), and 133 other domestic animals (1.2%). Among all animals received at the Wadsworth Center for rabies examination, 23.4% had reportedly bitten one or more persons, 22.2% had some other non- bite human contact, 31.3% had contact with one or more domestic animals, and 33.2% were non- contact surveillance specimens.
The 1,096 cases of rabies in animals during the year was again the largest total for any state, but was 13.4% fewer than the 1997 New York total (1,266), and 30.1% fewer than the average for the previous five year period (1,569). All but one of the cases in 1998 were diagnosed at the Wadsworth Center. A skunk captured in the Bronx was diagnosed at the New York City laboratory. Rabies in wildlife accounted for 96.4% (1,056) of all cases. There were 689 rabid raccoons, which was 147 (17.6%) fewer than 1997, and accounted for 62.9% of all rabid animals for the year. The 196 rabid skunks comprised 17.9% of all cases, and 110 rabid bats accounted for 10.0% of all cases. There were also 40 rabid gray foxes, 11 red foxes, 8 woodchucks, 1 whitetail deer and one river otter. The only other confirmed rabid otter reported from New York State occurred in 1991.
Among all animals received, the rabies positivity rate (rabid/tested) was 10.1%. The positivity rate among raccoons received was 31.6%, among skunks it was 28.2%, and for cats it was 1.2%. Among all rabid animals, 22.1% had reportedly bitten or scratched a human. Of the rabid raccoons, 14.9% had reportedly exposed a human. Remarkably, among the 40 rabid gray foxes, 70% (28/40) had reportedly exposed a human by bite or scratch. Of the 22 gray foxes received that were known to have actually bitten a human, 95.5% (21) were found to be rabid.
Rabies in Domestic Animals
Rabies was diagnosed in 40 domestic animals during the year, accounting for 3.6% of all cases. This was the first time since 1989 in which there was no rabid dog in the state. The 27 rabid cats was more than double the total of other rabid domestic animals combined, 28.6% greater than the 1997 total (21), but 12.9% fewer than the average for the previous five year period (31). Other rabid domestic species included 8 cattle, 4 horses, and 1 ferret. There was one previous rabid ferret in New York State, reported in 1995. One of 1998's rabid horses became infected with the raccoon rabies variant of rabies virus, despite current rabies vaccination (two annual doses). Because the exposure went unrecognized, the animal did not receive a postexposure booster vaccination. Such vaccine failures are rare. Nevertheless, this case is a strong reminder of the importance of the booster vaccination that is required within five days of a rabies exposure for a currently vaccinated animal. It also demonstrates the need to rule out rabies in biting animals by 10 day observation or testing, despite current vaccination status.
Rabies in Raccoons
The raccoon rabies outbreak spread into newly affected areas mainly at the epizootic front in St. Lawrence County, where the disease was reported in raccoons in 12 new towns during the year. The outbreak was very intense in the affected areas of the county: 140 terrestrial animal cases were reported, with only half of the county affected by the end of the year. Statewide, the outbreak affected 403 towns in 53 counties - only Franklin and Hamilton counties in the north, Suffolk and Nassau counties on Long Island, and Kings, Queens, Richmond (Staten Island) and New York (Manhattan) counties were free of reported terrestrial rabies during 1998.
Rabies in Bats
The 110 rabid bats confirmed in the state eclipsed by 31.0% the previous annual record of 84, recorded in 1990. This record number of rabid bats and the record number of bats received for testing (3,141), reflect the implementation of the modified national and state bat encounter guidelines. It is now recommended to capture and test bats encountered in many common circumstances, even in the absence of a recognized human exposure. The recent emphasis of rabies control programs on bat rabies and liberalized postexposure treatment guidelines was substantiated during the year by another human rabies death from a bat rabies variant, in the absence of a recognized bite. This death, which occurred in Virginia on December 31, brings to 20 the total of human rabies deaths attributed to bat rabies in the United States since 1990.
The overall positivity rate among bats examined in the state was 3.5%. It is noteworthy that this is not significantly different from the 1997 positivity rate among bats (3.4%), or the average for the previous five-year period (3.7%), or the average for the 17 year period 1981-1997 (4.0%). Once again, the big brown bat accounted for the vast majority of rabid bats and had a much higher total rabid (89) and positivity rate (4.6%) than the other common house bat, the little brown bat (11, 1.2%). Other rabid bats included 4 hoary bats, 1 silver-haired bat, 1 Keen's bat, 1 red bat, and 2 bats unidentifiable to species. Rabid bats were geographically widespread during 1998, with at least one case reported in 83 different towns in 37 of the state's 62 counties. Among all bats received at the Wadsworth Center for testing, 4.5% (140) had reportedly bitten a human, 15.2% (471) had some non- bite human contact, and 29% (900) had contact with one or more cats. Among the rabid bats, 10.9% (12) had reportedly bitten a human, 15.5% (17) had some non-bite human contact, and 22.7% (25) had contact with one or more cats. Of all bats received, 53.9% were male, 40.7% female, and 5.4% unidentified as to gender. Among the rabid bats 34.2% were male, 60.7% were female, and 5.1% were unidentified as to gender. There were three rabid juvenile bats identified among 129 examined, for a rabies-positivity rate among juvenile bats of 2.3%.
Human Serological Testing
Monoclonal antibody analysis was performed on 171 samples during the year, including rabid bats, domestic animals and cases in unusual species or locations. All wild terrestrial and domestic animals analyzed were found to be infected with the raccoon rabies variant of rabies virus, and all bats analyzed were infected with one of four bat rabies variants commonly identified in insectivorous bats of the northeast. The silver-haired/pipistrelle variant, implicated in most human rabies cases in the US since 1990, was identified only in the one rabid silver-haired bat analyzed. The Wadsworth Center rabies laboratory also performed rabies serologic assay for rabies antibody on 2,003 human samples during the year. The vast majority of these tests (89%) were done to determine the timing of booster vaccination. Fourteen human serum samples were tested (all negative) as part of the antemortem examination for rabies in patients with encephalitis of undetermined etiology.
(New York City data provided by Dr. Igbal Poshni, Director, Virus Laboratory, New York City Department of Health)