THE DISTRIBUTION OF DERMACENTOR HUNTERI AND ANAPLASMA SP IN DESERT BIGHORN SHEEP (OVIS-CANADENSIS)

The ixodid tick Dermacentor hunteri has been collected intermittently this century, primarily from desert bighorn sheep (Ovis canadensis). A naplasma spp. are intraerythrocytic rickettsial parasites of ungulates and are vectored in the western United States by ticks of the genus D ermacentor. We tested the hypotheses that D. hunteri would be found in festing all populations of desert bighorn, and that all infested popul ations would be seropositive for Anaplasma sp. Dermacentor hunteri was found on desert bighorn throughout their range in the Mojave and Sono ran deserts of the southwestern United States and northern Mexico, bur not in any portion of the Chihuahuan desert of New Mexico and eastern Arizona or in Baja California Sur, Mexico. Using an indirect immunofl uorescence antibody test (IIF), 8 populations of desert bighorn in Cal ifornia with D. hunteri were seropositive for Anaplasma sp. (n = 160). Four populations of desert bighorn with D. hunteri in Arizona (n = 69 ), 1 in Nevada (n = 22), and 1 in Utah (n = 14) with D. hunteri were s eronegative. Six populations of desert bighorn were uninfested with D. hunteri and were also seronegative. Of these populations, 1 was in Ca lifornia (n = 19), 2 were in New Mexico (n = 33), 2 were in Utah (n = 30), and 1 was in Baja California Sur (n = 14). We found no support fo r either of our original hypotheses and concluded that both D. hunteri and Anaplasma sp. are limited in their distribution among desert bigh orn. We also suggest a cautionary approach to translocations of desert bighorn given the high prevalence of ticks and the unknown effects of Anaplasma sp. on free-ranging bighorn.