Focal epidemic of sarcoptid (Acarina: Sarcoptidae) mite infestation in an insular population of white-footed mice

The abrupt and focal emergence of an infestation of sarcoptid mites was documented during long-term studies of populations of the white-footed mouse, Peromyscus leucopus (Rafinesque), on Nantucket Island, MA. From 1985 to 1990, >1,000 trap nights were recorded each year in 2 permanently situated sampling grids that were sampled monthly from April through November. In April 1995, prominent excrescences were first noted on the pinnae of mice trapped solely from 1 of the 2 sites. Histopathology of the lesions suggested infestation with Notoedres spp. Of 140 unique captures of mice during 1995-1997, 77% were infested, as determined by the presence or absence of macroscopic ear lesions. Both sexes were likely to be infested, but juvenile mice were twice as likely to be noninfested. No lesions were noted in 103 mice concurrently sampled from a grid situated 15 km away, nor in mice from other sites in coastal New England. The origin of this epidemic remains obscure. This unusual infestation exemplifies the emergence of zoonotic infections, but at the level of an enzootic cycle.