Reduced abundance of immature Ixodes dammini (Acari: Ixodidae) following incremental removal of deer.

The abundance of immature Ixodes dammini Spielman, Clifford, Piesman & Corwin was monitored for 9 yr (1983-1991) before and during the controlled, limited hunting of white-tailed deer, Odocoileus virginianus (Zimmerman), at a coastal Massachusetts site. Deer abundance was reduced from an estimated 350 during 1985 to approximately 60 during 1991. Although annual fluctuations were large, mean larval I. dammini abundance declined from 20.8 per white-footed mouse, Peromyscus leucopus (Rafinesque), during 1983-1986 before deer reduction to 10.3 per mouse following deer reduction (1987-1991). Similarly, mean nymphal I. dammini abundance declined from 2.7 per mouse before intervention to 1.6 per mouse after intervention. Immature I. dammini population fluctuations were not associated with those of P. leucopus. The total population of larvae infesting P. leucopus declined from 3,596 ticks before intervention to 1,535 ticks after intervention. Concurrently, the total nymphal population declined from 417 ticks before intervention to 187 ticks after intervention. The number of feeding adult female I. dammini on deer increased as deer density decreased.

Efficacy of a permethrin-based acaricide to reduce the abundance of Ixodes dammini (Acari: Ixodidae).

Permethrin-impregnated cotton was distributed to reduce abundance of immature Ixodes dammini Spielman, Clifford, Piesman & Corwin feeding upon white-footed mice (Peromyscus leucopus) and questing on vegetation at a private resort site (The Crane Reservation of The Trustees of Reservations in Ipswich, Mass.) located in coastal New England. This test constituted the first independent evaluation of the efficacy of this commercial product (Damminix). Over a 3-yr period, 2,000 applicator tubes containing treated cotton were distributed over the 7.3-ha site in 5 regularly scheduled applications. Mice removed treated fiber from the tubes and transported it to their nests. Within 3 wk of the first application, virtually all mice in the treated site were rendered free of ectoparasites. After the first season of application, no nymphal host-seeking I. dammini could be found on vegetation. Visitor and employee complaints about deer tick bites or ticks found on skin and clothing had been attributed to the site before treatment, but not thereafter. We confirmed the efficacy of Damminix for reduction of the abundance of vector ticks and thereby contributed to the protection of humans against Lyme disease at this site.

Rapid emergence of a focal epidemic of Lyme disease in coastal Massachusetts.

We describe a focal epidemic of Lyme disease, which spread from a nature preserve and affected an adjacent community of permanent residents in coastal Massachusetts. The attack rate from 1980 through 1987 was 35 percent among 190 residents living within 5 km of the nature preserve and was greatest (66 percent) among those living closest to the preserve. The risk of infection bore little relation to sex or age. Late Lyme disease, which clustered near the preserve, occurred mainly in residents infected early in the epidemic who did not have a history of erythema migrans and did not receive antibiotic therapy. All the residents with serologic evidence of infection had early or late clinical manifestations of Lyme disease, or both, during the period of study. The seasonal risk of infection was bimodal--greatest in June, with a secondary peak in October--and corresponded to periods of increased transmission. In the nature preserve, the density of the vector tick, Ixodes dammini, exceeded that in other New England sites. The zoonosis rapidly became endemic, and the severity of its impact correlated with the abundance of deer. This epidemic of Lyme disease demonstrated that outbreaks can be focal and can spread rapidly within a community of permanent residents.