Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2006
Publication Date: 9/1/2006
Citation: Scoles, G.A., Mcelwain, T.F., Rurangirwa, F.R., Knowles Jr, D.P., Lysyk, T.J. 2006. A Canadian Bison Isolate of Anaplasma marginale (Rickettsiales: Anaplasmataceae) Is Not Transmissible by Dermacentor andersoni (Acari: Ixodidae), Whereas Ticks from Two Canadian D. andersoni Populations Are Competent Vectors of a U.S. Strain. Journal of Medical Entomology. 43(5): 971-975. Interpretive Summary: Anaplasma marginale is a tick-transmitted pathogen of cattle that can be found throughout tropical temperate areas of the world. In the northwestern United States Anaplasma is normally transmitted by the Rocky Mountain wood tick. Anaplasmosis can be found in regions within the United States but Canadian cattle appear to be free of infection. Anaplasma infection has been found in a small number of farm raised bison in central Saskatchewan but transmission from bison to cattle hasn't happened, even though we know that the bison strain can infect cattle. One explanation for this might be that the bison Anaplasma can't be transmitted by wood ticks the way most strains are. In our experiments wood ticks from the United States and Canada did not transmit the Saskatchewan bison Anaplasma. In a separate experiment wood ticks from Alberta and British Columbia were able to transmit an Idaho strain of Anaplasma. These data show that the apparent absence of Anaplasmosis from the Canadian cattle population is not because Canadian wood ticks are unable to transmit. Even though the Saskatchewan bison Anaplasma can't be transmitted by wood ticks, if tick transmissible strains like the Idaho strain are introduced, Canadian tick populations would be able to transmit them.
Technical Abstract: Anaplasma marginale Theiler is a tick-borne rickettsial pathogen of cattle with a global distribution in both temperate and tropical regions. The pathogen is endemic in regions within the United States, while Canadian cattle are considered to be A. marginale free. A. marginale has been isolated from farmed bison (Bison bison) in central Saskatchewan, however, there is no evidence of transmission from bison to cattle. In this study we test the hypothesis that a Saskatchewan bison isolate of A. marginale was not transmissible by Dermacentor andersoni ticks. Colonized D. andersoni strains from the United States and Canada failed to transmit the Saskatchewan bison isolate. A separate transmission trial using D. andersoni adults reared from ticks collected in Alberta and British Columbia showed that these populations could successfully transmit the St. Maries, Idaho strain of A. marginale. These data suggest that the apparent absence of A. marginale from the Canadian cattle population cannot be accounted for by the inability of Canadian D. andersoni populations to transmit. Although the Saskatchewan bison isolate of A. marginale appears not to be transmissible by D. andersoni, in the event of an introduction or outbreak of a tick transmissible strain, Canadian D. andersoni populations would be fully competent vectors.