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Update: Raccoon Rabies Epizootic -- United States and Canada, 1999

In 1977, an outbreak of raccoon rabies was detected in an area on the West Virginia-Virginia border (1). Since then, the area affected by this distinct variant of rabies virus associated with raccoons has spread to Ohio in the west and New York, Pennsylvania, Vermont, New Hampshire, and Maine in the north (Figure 1). In addition, the once separate epizootics of rabies among raccoons in the southeastern and mid-Atlantic states converged in North Carolina. In July 1999, the raccoon rabies virus variant was reported from Ontario, Canada, on the New York border. This report describes the spread of this epizootic of raccoon rabies through mid-Atlantic and northeastern states and into Canada.

Canada. On July 14, 1999, the first case of rabies caused by the raccoon-associated variant was diagnosed in a raccoon across the St. Lawrence River from Ogdensburg, New York, in a village northwest of Prescott, Ontario. A second case was identified on July 26, 9 miles west of the first case. A third case was diagnosed on September 17, approximately 9 miles north of the other two cases. The Ontario Ministry of Natural Resources (OMNR) has been conducting trap-vaccinate-release programs for several years at the major border crossings in the St. Lawrence and Niagara areas to build defensive zones of vaccinated raccoons to minimize the spread of epizootic rabies. These first cases occurred outside the vaccinated zone. A total of 880 raccoons, 220 striped skunks, and one red fox, captured within a 3-mile radius of each of the first two cases, were negative for rabies by immunofluorescence test (OMNR, unpublished data, 2000). In approximately 3 miles around the point-control area, raccoons and skunks were caught in live traps, vaccinated with an inactivated vaccine, and released. Raccoons with rabies probably crossed the St. Lawrence through or near the international bridge between Ogdensburg-Johnstown, New York, and Prescott, Ontario.

Maine. In August 1994, the raccoon-associated variant of rabies virus was first detected in Maine. During August 1994-August 1999, 857 rabid animals were identified, 85% of which were infected or presumed infected with the raccoon rabies variant. As of August 1999, 13 of 16 Maine counties were affected by the raccoon rabies variant. This variant also is occurring with increasing frequency in skunks.

New Hampshire. Cases of rabies believed caused by the raccoon-associated variant of rabies virus peaked in 1994 with 140 raccoons testing positive for rabies. Since 1994, the number of rabies cases decreased to 26 in 1996 and to 18 in 1997, with a slight increase to 23 in 1998. Reports in 1999 include two cats confirmed with the raccoon rabies variant and 18 raccoons.

New York. Since 1990, the raccoon-associated variant of rabies virus has spread to all but one northern county, two counties on eastern Long Island, and one New York City borough. In 1998, New York reported 1096 laboratory-confirmed rabies cases in animals; this marked the eighth consecutive year with greater than 1000 cases. This epizootic has been associated with raccoon rabies in domestic and wild animals, including one black bear and 31 white-tailed deer.

North Carolina. The raccoon rabies epizootic continues to spread to the east and west and affects greater than 80% of North Carolina counties. Rabies has been found in western North Carolina in Watauga County, approximately 6 miles from the Tennessee border. No cases of rabies among raccoons have been reported from neighboring Tennessee counties.

Ohio. In early 1997, rabies among raccoons was first reported from northeastern Ohio. By the end of 1997, three counties bordering Pennsylvania reported 62 rabid animals, including 59 raccoons. Within 2 months of confirmation of the outbreak, the Ohio Department of Health (ODH), with support from CDC and the U.S. Department of Agriculture, implemented an oral rabies vaccination (ORV) program in counties along the Pennsylvania border. In May and September 1997 and in April and October 1998, ORV treatment was delivered. In May and September 1999, ODH distributed 1,459,442 vaccine-laden baits for animals; the treatment area covered 4037 square miles. After implementing ORV, reported cases of animals infected with the raccoon-associated rabies variant decreased to 26 (20 raccoons) in 1998. As of November 11, five raccoons and a chipmunk infected with the raccoon-associated rabies variant have been reported in 1999.

Vermont. The raccoon-associated variant of rabies virus was first identified in Vermont in 1994. By 1998, the epizootic had progressed into the north central counties of the state. An ORV campaign along the Canadian border initiated in 1997 appears to have decreased the reported number of rabies cases in that region, and no rabies has been reported associated with this variant across the Canadian border.

Virginia. In 1978, raccoon rabies was first identified in Virginia in a county bordering the West Virginia county that initially reported the new outbreak in 1977. Counties in southwestern Virginia continue to be affected by raccoon rabies. In 1998 and 1999, cases have been reported as far west as Russell and Washington counties.

West Virginia. Raccoon rabies became established in eastern West Virginia in approximately 1977. The Appalachian Mountains presented a barrier to the westward spread of the raccoon-associated rabies variant; however, in 1997, a rabid raccoon was found in Ritchie County, one county east of the Ohio River. In 1999, 23 rabid raccoons were identified from Monongalia and Marion counties on the northwestern border.

Reported by: AI Wandeler, PhD, Center of Expertise for Rabies, Animal Diseases Research Institute, Canadian Food Inspection Agency; RC Rosatte, Rabies Unit, Wildlife Research Section, Ontario Ministry of Natural Resources. D Williams, TK Lee, DrPH, KF Gensheimer, MD, State Epidemiologist, Maine Dept of Human Svcs. JT Montero, MD, Bur of Communicable Disease Control, New Hampshire Dept of Health and Human Svcs. CV Trimarchi, DL Morse, MD, M Eidson, DVM, PF Smith, MD, State Epidemiologist, New York State Dept of Health. JL Hunter, DVM, North Carolina Dept of Health and Human Services. KA Smith, DVM, Ohio Dept of Health. RH Johnson, DVM, Vermont Dept of Health. SR Jenkins, VMD, Virginia Dept of Health. C Berryman, DVM, Div of Surveillance and Disease Control, West Virginia Dept of Health and Human Resources. Viral and Rickettsial Zoonoses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; and an EIS Officer, CDC.

Editorial Note:

Raccoons have accounted for the largest percentage of animal rabies cases reported to CDC since 1990. In 1998, 44% of all rabies cases among animals in the United States occurred among raccoons. From 1990 to 1998, 35,264 cases of raccoon rabies were reported in the United States. Of those 35,033 (99.3%) occurred in eastern states where raccoon rabies is enzootic.

Since the start of the mid-Atlantic epizootic of rabies involving the raccoon-associated variant of rabies virus, the epizootic front has progressed at approximately 18-24 miles each year (2-4). The progress of the epizootic appears most rapid in preferred raccoon habitats; however, major physiographic barriers, such as rivers and mountain ranges, can impede the epizootic advance (3-5). Although the Appalachian Mountains slowed the westward progression of the epizootic for more than a decade, counties in western Virginia and western North Carolina are reporting raccoon rabies cases. The threat of rabies introduction into counties in eastern Ohio soon may include much of the border with West Virginia in addition to the border with Pennsylvania. Once raccoon rabies becomes established in the Ohio River valley, few physio-graphic barriers remain to prevent its spread throughout the midwestern United States.

In the northern United States, the raccoon-associated variant of rabies virus has crossed the St. Lawrence River and reached Canada. As of January 2000, eight cases of raccoon rabies have been found in Ontario (RC Rosatte, OMNR, personal communication, 2000). Whether Canadian attempts at outbreak intervention (6) involving local raccoon population control and establishing an immune barrier are successful will require ongoing active surveillance. However, incursions of infected raccoons into Canada from other sites along the U.S. border where rabies is endemic will continue to occur unless control efforts on both sides of the border are effective.

Although human rabies is rare in the United States and Canada, the costs associated with rabies prevention are substantial (2,7). Where epizootics of raccoon rabies have occurred, the number of costly human postexposure treatments has increased dramatically (8). Although ORV immune barriers to prevent epizootic spread of wildlife rabies exist in several states, their maintenance requires substantial annual expenditures (9). Even when economic arguments for the use of wildlife rabies control in certain circumstances exist, active intervention to control wildlife rabies and public support for these activities in the United States are limited. The usefulness of ORV showed that targeting raccoon habitats with ORV increased vaccination rates to 63%, which was sufficient to halt the spread of rabies in free-ranging raccoons (10). However, ORV or other methods for eliminating or reducing rabies cases among raccoons after the disease has become endemic are generally unproven and need further assessment. In addition to educational initiatives and effective public health surveillance, prevention of human and domestic animal rabies primarily relies on the public to keep pets vaccinated and to reduce the number of stray animals.

References

  1. Jenkins SR, Perry BD, Winkler WG. Ecology and epidemiology of raccoon rabies. Rev Infect Dis 1998;10(suppl)4:S620-S625.
  2. Rupprecht CE, Smith JS. Raccoon rabies: the re-emergence of an epizootic in a densely populated area. Semin Virol 1994;5:155-64.
  3. Wilson ML, Bretsky PM, Cooper GH, et al. Emergence of raccoon rabies in Connecticut, 1991-1994: spatial and temporal characteristics of animal infection and human contact. Am J Trop Med Hyg 1997;57:457-63.
  4. Moore DA. Spatial diffusion of raccoon rabies in Pennsylvania. Prev Vet Med 1999;40:19-32.
  5. Carey AB, Giles RH, McLean RG. The landscape epidemiology of rabies in Virginia. Am J Trop Med Hyg 1978;27:573-80.
  6. Rosatte RC, Howard DR, Campbell JB, MacInnes CD. Intramuscular vaccination of skunks and raccoons against rabies. J Wildl Dis 1990;26:225-30.
  7. Fishbein DB, Arcangeli S. Rabies prevention in primary care: a four-step approach. Postgrad Med 1987;82:83-90,93-5.
  8. CDC. Update: raccoon rabies epizootic--United States, 1996. MMWR 1997;45:1116-20.
  9. Meltzer MI, Rupprecht CE. A review of the economics of the prevention and control of rabies. Part 2: rabies in dogs, livestock and wildlife. Pharmacoeconomics 1998;13:481-98.
  10. Robbins AH, Borden MD, Windmiller BS, et al. Prevention of the spread of rabies to wildlife by oral vaccination of raccoons in Massachusetts. JAVMA 1998;213:1407-12.

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