Experimental transmission of bovine anaplasmosis (caused by Anaplasma marginale) by means of Dermacentor variabilis and D. andersoni (Ixodidae) collected in western Canada.
Canadian cattle are free of bovine anaplasmosis, with the exception of 4 isolated incursions since 1968, which were eradicated. It is not known why the disease has not become established in regions of Canada adjacent to the United States where it is endemic. To assess the vector competence of wild-caught ticks in cattle-rearing regions, Dermacentor variabilis and D. andersoni were collected in western Canada and fed on calves experimentally infected with Anaplasma marginale (St. Maries strain). The 2 tick species were equally competent in transmitting A. marginale to splenectomized calves, all 15 tick-exposed calves becoming infected. The prepatent periods in 13 calves ranged from 18 to 26 d and did not vary in relation to the numbers of ticks fed or the duration of transmission feedings. The unusually long prepatent periods in 2 calves (45 and 55 d) were probably due to concomitant Eperythrozoon infection. This study clearly demonstrated that tick species present in western Canada are competent vectors of bovine anaplasmosis. Potential barriers, including climate, must be considered in developing strategies to prevent A. marginale from becoming established in anaplasmosis-free regions.
Lankester
Murray W
MW
Canadian Food Inspection Agency (CFIA), Saskatoon Laboratory, Centre for Food-Borne & Animal Parasitology, 116 Veterinary Road, Saskatoon, Saskatchewan S7N 2R3.
Scandrett
W Brad
WB
Golsteyn-Thomas
Elizabeth J
EJ
Chilton
Neil C
NC
Gajadhar
Alvin A
AA
D042322:Anaplasma marginale; D000712:Anaplasmosis / Q000635:transmission*; D000818:Animals; D001096:Arachnid Vectors / Q000382:microbiology*; D002170:Canada; D002417:Cattle; D002418:Cattle Diseases / Q000635:transmission*; D003870:Dermacentor / Q000382:microbiology*; D008297:Male; D011897:Random Allocation