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Rabies in a Beaver --- Florida, 2001

On November 25, 2001, a beaver exhibited aggressive behavior by charging canoes and kayaks on the Ichetucknee River in Alachua County, Florida. The beaver was captured by park personnel and submitted to a Florida Department of Health (FDoH) laboratory for rabies testing. Park rangers contacted the Alachua County Health Department after they identified five persons who were in the vicinity of the animal before capture. These five persons were interviewed by county health department personnel, who reported that although the beaver had made aggressive actions, the animal had not bitten anyone. This report summarizes the investigation of this case of animal rabies. Mammals that exhibit aggressive or other unusual behavior should be reported promptly to local health officials and should not be approached or handled by the public.

On November 27, the FDoH laboratory diagnosed rabies in the brain tissue of the beaver by using a fluorescent antibody test. Monoclonal antibody strain typing indicated that the virus belonged to the antigenically distinct group of viruses found in raccoons in the eastern United States. Park personnel involved in the capture of the animal received postexposure prophylaxis. No treatment was recommended for the five persons who had been in the vicinity.

Of 3,751 animal specimens submitted for rabies testing to the FDoH during 2001, a total of 198 (5.3%) tested positive for rabies. In addition to the beaver, specimens included 124 raccoons, 34 foxes, 19 bats, 15 cats, two otters, one dog, one bobcat, and one horse. In 2001, no other rabid animals were identified in Alachua County. However, seven raccoons, four bats, three foxes, and one dog were reported with rabies in neighboring counties.

Reported by: T Belcuore, MSM, Alachua County Health Dept, Gainesville; L Conti, DVM, V Mock, S Wiersma, MD, State Epidemiologist, Florida State Dept of Health. J Childs, ScD, C Rupprecht, VMD, C Hanlon, VMD, J Krebs, MS, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; M Guerra, DVM, EIS Officer, CDC.

Editorial Note:

This report describes the first finding of rabies in a beaver in Florida. Although rodents are not a wildlife reservoir for rabies virus and no rabies transmission from rodents to humans has been documented, reported cases of rabies in rodents have been increasing in the United States, from 97 cases during 1971--1984 (1) to an average of 52 cases per year during 1995--2000 (2--7). This trend is attributed to an increase in cases among large rodents (e.g., woodchucks [Marmota monax] and beavers [Castor canadensis]), with most cases occurring in the eastern states, where a raccoon rabies epizootic has been documented (3,8).

Reported rabies in Florida rodents is uncommon. Woodchucks are not native to Florida, and the natural range of the beaver is restricted to the northern portion of the state. Large rodents share habitats with terrestrial carnivore rabies reservoirs (e.g., raccoons, skunks, and foxes) and because of their size have a greater chance of surviving an encounter with a rabid carnivore. In these areas, rabies should be considered in the differential diagnosis of any mammal with unexplained neurologic illness. Possible human and pet exposures to rabies should be evaluated by public health officials on an individual basis. Bites from small rodents that are unlikely to survive an encounter with a rabid animal rarely require rabies postexposure prophylaxis; however, bites from large rodents should be considered as possible rabies exposures, especially in areas where rabies is endemic (9). Persons should avoid any mammal exhibiting aggressive or unusual behavior. Persons who suspect that they have been exposed to a rabid animal should contact a health-care provider immediately.

References

  1. Fishbein DB, Belotto AJ, Pacer RE, et al. Rabies in rodents and lagomorphs in the United States, 1971--1984: increased cases in the woodchuck (Marmota monax) in mid-Atlantic states. J Wildl Dis 1986;22:151--5.
  2. Krebs JW, Strine TW, Smith JS, Noah DL, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1995. J Am Vet Med Assoc 1996;209:2031--44.
  3. Krebs JW, Smith JS, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1996. J Am Vet Med Assoc 1997;211: 1525--39.
  4. Krebs JW, Smith JS, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1997. J Am Vet Med Assoc 1998;213: 1713--28.
  5. Krebs JW, Smith JS, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1998. J Am Vet Med Assoc 1999;215: 1786--98.
  6. Krebs JW, Smith JS, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1999. J Am Vet Med Assoc 2000;217: 1799--1811.
  7. Krebs JW, Mondul AM, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 2000. J Am Vet Med Assoc 2001;219: 1687--99.
  8. Childs JE, Colby L, Krebs JW, et al. Surveillance and spatiotemporal associations of rabies in rodents and lagomorphs in the United States, 1985--1994. J Wildl Dis 1997;33:20--7.
  9. CDC. Human rabies prevention---United States, 1999: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1999;48(No. RR-1).

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