Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/1996
Publication Date: N/A
Interpretive Summary: Anaplasmosis is a disease of domestic and wild ungulates such as sheep, cattle, deer, elk, bighorn sheep, etc., and is caused by microorganisms in a group referred to as rickettsia. The rickettsia are transmitted by blood feeding arthropods (biting flies and ticks), and in the western U.S., ticks of the genus Dermacentor are responsible for natural transmission. The importance of the disease in wildlife remains unclear, but is becoming more fully understood and appreciated. Since the disease represents a health threat to both domestic livestock and wildlife under certain conditions, it is important to further delineate the areas where the disease occurs in wildlife, and identify factors involved in the transmission, and thus maintenance of the disease, particularly in areas where wildlife and livestock share habitat.. In areas of the desert southwest, where Anaplasma has been found associated with desert bighorn sheep, the only tick found on bighorn sheep are Dermacentor hunteri. This study established the range of D. hunteri in bighorn sheep populations in the southwest, and provided evidence that not all herds are infested with these ticks. Also not all herds that are infested necessarily have been exposed to Anaplasma rickettsia. However, in each case where anaplasmosis was diagnosed, the herds involved were infested with this tick species. This information is useful to wildlife managers who make decisions concerning translocation of individual bighorn sheep from herds in one area to herds in another.
Technical Abstract: The ixodid tack Demacentor hunteri has been collected intermittently this century, primarily from desert bighorn sheep. Anaplasma spp. are intraerythrocytic rickettsial parasites of ungulates and are vectored in the western United States by ticks of the genus Demacentor. We tested the hypotheses that D. hunteri would be found infecting all populations of desert bighorn, and that all infested populations would be seropositive for Anaplasma sp. Dermacentor hunteri was found on desert bighorn throughout their range in the Mojave and Sonoran deserts of the southwestern United States and northern Mexico, but not in any portion of the Chihuahuan desert of New Mexico and eastern Arizona or in Baja California Sur, Mexico. Using an indirect immunofluorescence antibody test, 8 populations of desert bighorn in California with D. hunteri were seropositive for Anaplasma sp. Four populations of desert bighorn with D. hunteri in Arizona, 1 in Nevada, and 1 in Utah with D. hunteri were seronegative. Six populations of desert bighorn were uninfested with D. hunteri and were also seronegative. Of these populations, 1 was in California, 2 were in New Mexico, 2 were in Utah and 1 was in Baja California Sur. We found no support for either of our original hypotheses and concluded that both D. hunteri and Anaplasma sp. are limited in their distribution among desert bighorn. We also suggest a cautionary approach to translocations of desert bighorn giben the high prevalence of ticks and the unknown effects of Anaplasma sp. on free-ranging bighorn.