VECTOR COMPETENCE OF IXODES-PACIFICUS AND DERMACENTOR-OCCIDENTALIS (ACARI, IXODIDAE) FOR VARIOUS ISOLATES OF LYME-DISEASE SPIROCHETES

The vector competence of the western black-legged tick, Ixodes pacific us Cooley & Kohls, and the Pacific Coast tick, Dermacentor occidentali s Marx, for the Lyme disease spirochete (Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner) was compared. Rabbits, hamsters, and the deer mouse, Peromyscus maniculatus (Wagner), were injected wi th cultured spirochetes or infected tick-suspensions, or were fed upon by spirochete-infected ticks. Five of seven isolates used as inocula were reisolated from vertebrates with the ear-punch biopsy technique. Three isolates (CA4, 5, 7) that were infectious for both vertebrates a nd ticks possessed prominent low-molecular-weight protein bands that h ad relative mobilities of almost-equal-to 24-26 kd. The ability of tic ks to acquire and maintain various inocula of B. burgdorferi was evalu ated by feeding uninfected larvae xenodiagnostically on all three host s 0-63 d postinjection. Low percentages (0-10.6%) of the I. pacificus and none of the D. occidentalis became infected. By contrast, 33% of I . pacificus and 40% of Ixodes scapularis Say (= I. dammini Spielman, C lifford, Piesman & Corwin) that fed on hamsters infected by tick-bite acquired and transstadially passed spirochetes; 10% of D. occidentalis fed on infected hamsters similarly acquired but did not maintain spir ochetes. Ixodes pacificus nymphs efficiently transmitted B. burgdorfer i to deer mice and a hamster. Feeding by one spirochete-infected nymph was sufficient to produce patent infections in each of five mice.