Anaplasma marginale is endemic in several areas of the United States. Cattle that survive acute infection with become persistently infected carriers with a low rickettsemia that is undetectable by microscopy. Dermacentor andersoni, the Rocky Mountain wood tick, is the most important vector of A. marginale. Ticks can acquire and biologically transmit the pathogen during the persistent phase of infection. Questing adult D. andersoni were collected from 6 natural populations and tested for susceptibility to infection with A. marginale. Ticks from a 15 year old laboratory colony established from adults collected at the Reynolds Creek Watershed in Southwestern Idaho were tested for comparison. Male ticks were fed on a steer that was persistently infected with a strain of A. marginale isolated from St. Maries in north-central Idaho. Ticks were held for 10 days, then guts and salivary glands were dissected and tested for A. marginale using PCR. Only 3/24 (12.5%) of the colonized ticks had A. marginale infected guts, whereas guts of 15/24 (62.5%) ticks from a rangeland site were infected. Infection rates in the other 5 field collected populations ranged from 12.5% (Hamilton, MT) to 50% (Walker Lake, BC, Canada). Infection of the gut is a key component of tick vector competence; this is the first demonstration of population level variation in a key component of tick vector competence for this or any other tick-borne pathogen. Additional transmission trials using both colonized and field collected ticks are ongoing, as are studies of the population genetics of D. andersoni.
Species 1: Acari Ixodidae Dermacentor andersoni (Rocky Mountain wood tick)
Species 2: Rickettsiales Ehrlichiaceae Anaplasma marginale
Keywords: vectors, Anaplasma
Back to Symposium: Acarology Society Symposium--Ticks and Mites as Vectors of New and Re-Emerging Diseases
Back to Symposia
Back to The 2003 ESA Annual Meeting and Exhibition