QUANTITATION OF THE BORRELIA-BURGDORFERI OUTER SURFACE PROTEIN-A IN IXODES-SCAPULARIS - FLUCTUATIONS DURING THE TICK LIFE-CYCLE, DOUBLING TIMES, AND LOSS WHILE FEEDING

The presence of outer surface protein A (OspA) as a marker for Borreli a burgdorferi in Ixodes scapularis ticks was monitored with an OspA an tigen-capture ELISA. The OspA ELISA, with a sensitivity of 30 spiroche tes (8 fg), was not affected by the presence of either recently blood- fed or flat tick homogenates. Median spirochete equivalent levels as h igh as 16,000 in larvae, 55,000 in attached nymphs, and 10,000 in unfe d adults were observed. Estimates of OspA doubling times ranged from a maximum of 140 h in larvae to as short as 17.5 h during nymphal attac hment to the host. Spirochete equivalents in nymphs fell by 3 X 10(4) spirochete equivalents (54% of total OspA) in the last 12 h of attachm ent to mice but rose after detachment. Each OspA-positive I. scapulari s nymph, regardless of spirochete equivalent density or length of atta chment, successfully transmitted B. burgdorferi to a mouse.