Dermacentor hunteri (Acari : Ixodidae): an experimental vector of Anaplasma marginale and A-ovis (Rickettsiales : Anaplasmataceae) to calves and sheep?

The experimental vector competence of laboratory-reared Dermacentor hunteri Bishopp for Anaplasma marginale Theiler and Anaplasma ovis Lestoquard was evaluated by delayed transfer of male ticks from infected to susceptible Ho lstein calves and from infected to susceptible domestic sheep, respectively . After feeding for 4 or 5 d on rickettsemic acquisition hosts, the ticks w ere held off the host at 26 degrees C, approximate to 93% RH, and a photope riod of 14:10 (L:D) h for 7 or 8 d, then test fed for 5 or 7 d. Additionall y, ticks test-fed for 5 d on 2 susceptible calves were removed, held off th e host for 7 d, and test-fed for 5 d on a 3rd susceptible calf to test the tick's ability to transmit A. marginale by delayed serial transfer. Tick tr ansmission of A. marginale to 3 test calves and A. ovis to 3 test sheep was demonstrated by blood smear and indirect immunofluorescence serology. Thes e data indicate that males of D, hunteri, a tick commonly found on desert b ighorn,Ovis canadensis Shaw, in the southwestern United States and northern Mexico, may be competent natural vectors of these organisms present in des ert bighorn populations.