Prevalence of Borrelia burgdorferi in host-seeking ticks (Acari: Ixodidae) from a Lyme disease endemic area in northern Michigan.

The Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, was recovered from the guts of questing Ixodes scapularis Say adults and nymphs and adult Dermacentor variabilis (Say), collected in Menominee County, Michigan, in 1992. Spirochetes were cultured successfully from guts placed in modified Barbour-Stoenner-Kelly II medium held in 5-ml cultures tubes or in 0.3-ml wells of microtiter plates. Most isolates were recovered within 2 wk of culturing at an incubation temperature of 34 degrees C. Spirochetes were recovered more rapidly in culture tubes than in microtiter plates. For determination of tick infection with B. burgdorferi, culturing was equivalent to examination of gut smears by immunofluorescence. We found the following infection rates: 57/179 I. scapularis females (31.8%), 62/204 I. scapularis males (30.4%), 9/54 I. scapularis nymphs (16.7%), and 5/383 D. variabilis adults (1.3%).