Effectiveness of Residential Acaricides to Prevent Lyme and Other Tick-borne Diseases in Humans

Background. In the northeastern United States, tick- borne diseases are a major public health concern. In controlled studies, a single springtime application of acaricide has been shown to kill 68%- 100% of ticks. Although public health authorities recommend use of acaricides to control tick populations in yards, the effectiveness of these pesticides to prevent tick bites or human tick- borne diseases is unknown. Methods. We conducted a 2- year, randomized, double- blinded, placebo- controlled trial among 2727 households in 3 northeastern states. Households received a single springtime barrier application of bifenthrin or water according to recommended practices. Tick drags were conducted 3- 4 weeks after treatment on 10% of properties. Information on human- tick encounters and tick- borne diseases was collected through monthly surveys; reports of illness were validated by medical record review. Results. Although the abundance of questing ticks was significantly lower ( 63%) on acaricide- treated properties, there was no difference between treatment groups in human- tick encounters, self- reported tick- borne diseases, or medical- record- validated tickborne diseases. Conclusions. Used as recommended, acaricide barrier sprays do not significantly reduce the household risk of tick exposure or incidence of tick- borne disease. Measures for preventing tick- borne diseases should be evaluated against human outcomes to confirm effectiveness.