We determined that antibody responses to Psoroptes sp. mites were not present in 403 of 407 sera samples collected opportunistically from 1979 through 1991 from Dall sheep (Ovis dalli) from five locations in Alaska, USA (Eastern Arctic, n = 61; Central Arctic, n = 15; Western Interior, n = 122; Central Interior, n = 63; Eastern Interior, n = 146). Test values for four samples exceeded the positive cutoff value for the immunoassay, but exposure to mites could not be confirmed since the 95% confidence interval for true prevalence ranged from 0 to 2.3%. Therefore, we concluded that these were probably false positive results. Our analysis, coupled with the lack of previous reports of mites or lesions in Dall sheep or other Alaskan ungulates, provided indirect evidence that Psoroptes sp. are not enzootic in Dall sheep in Alaska. In contrast, Psoroptes sp. have been reported in bighorn sheep (Ovis canadensis) and other wild ungulate populations from southern Canada to Mexico. These findings are compatible with the hypothesis that Psoroptes sp. were introduced into North America with imported domestic sheep and were not introduced by ancestral wild sheep.
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Vol. 32 • No. 4