Effective control of the motile stages of Amblyomma americanum and reduced Ehrlichia spp. prevalence in adults via permethrin treatment of white-tailed deer in coastal Connecticut, USA.

The lone star tick, Amblyomma americanum, is a common human-biting species whose range has been largely restricted to the southeastern United States, until recent detections of established populations on Long Island, New York and throughout coastal southern New England. We evaluated the effectiveness of topical treatment of 10 % permethrin delivered via 4-poster devices to white-tailed deer, Odocoileus virginianus, in the management of a newly discovered A. americanum population in Norwalk, Connecticut. Using a high-density deployment of one 4-poster device/12.7 ha, we were successful in significantly reducing densities of host-seeking adults (93 % reduction), nymphs (92 %), and larvae (96 %) from 2018 to 2020. We also documented a significant reduction (87 %) in parasitizing adults and nymphs on white-tailed deer from 2018 to 2019. The prevalence of Ehrlichia chaffeensis and Ehrlichia ewingii combined in host-seeking adults declined significantly from 47 % at the time the A. americanum population was discovered in 2017 to 7% in 2020. However, the prevalence in nymphs remained static (∼9%) throughout the study period. These data demonstrate that, when properly deployed in a density-dependent manner in terms of deer abundance, 4-poster devices can effectively manage parasitizing and host-seeking A. americanum populations and reduce the prevalence of two ehrlichial species of public health importance.

Distribution and Establishment of the Lone Star Tick in Connecticut and Implications for Range Expansion and Public Health.

In the United States, the lone star tick, Amblyomma americanum (L.) (Acari: Ixodidae), is an aggressive southeastern species whose range has reportedly been steadily expanding northward. The number of A. americanum specimens submitted to the Tick Testing Laboratory (TTL) at the Connecticut Agricultural Experiment Station (CAES) increased by 58% from the period of 1996-2006 (n = 488) to 2007-2017 (n = 773), mainly from Fairfield County in the southwestern corner of the state. The greatest numbers of A. americanum submissions to the CAES-TTL were from the City of Norwalk and a few adjacent municipalities. We also report the discovery of a large infestation of adult and nymphal lone star ticks detected on a dead male white-tailed deer, Odocoileus virginianus (Zimmerman) (Artiodactyla: Cervidae), on Manresa Island, Norwalk, in June 2017, indicating a long established, undetected population along the southwestern coast. A sample of nymphal and adult host-seeking A. americanum collected July 2017 from Manresa Island were tested and a proportion were positive for Ehrlichia chaffeensis, Ehrlichia ewingii, and Anaplasma phagocytophilum. The A. americanum tick and its associated disease pathogens are expected to become an increasing public health concern in southern New England.

The relationship between deer density, tick abundance, and human cases of Lyme disease in a residential community.

White-tailed deer (Odocoileus virginianus Zimmerman), serve as the primary host for the adult blacklegged tick (Ixodes scapularis Say), the vector for Lyme disease, human babesiosis, and human granulocytic anaplasmosis. Our objective was to evaluate the degree of association between deer density, tick abundance, and human cases of Lyme disease in one Connecticut community over a 13-yr period. We surveyed 90-98% of all permanent residents in the community six times from 1995 to 2008 to document resident's exposure to tick-related disease and frequency and abundance of deer observations. After hunts were initiated, number and frequency of deer observations in the community were greatly reduced as were resident-reported cases of Lyme disease. Number of resident-reported cases of Lyme disease per 100 households was strongly correlated to deer density in the community. Reducing deer density to 5.1 deer per square kilometer resulted in a 76% reduction in tick abundance, 70% reduction in the entomological risk index, and 80% reduction in resident-reported cases of Lyme disease in the community from before to after a hunt was initiated.

The use of deer vehicle accidents as a proxy for measuring the degree of interaction between human and deer populations and its correlation with the incidence rate of Lyme disease.

The study described in this article examined the relationship between the incidence rate of deer vehicle accidents (DVAs), a proxy for measuring the interaction between populations of humans and deer, and human Lyme disease incidence rate. The authors also examined the relationship between deer population density and human Lyme incidence rate. They analyzed data from Connecticut's Department of Environmental Protection and the Department of Public Health from 1999 through 2008 by deer management zone (DMZ) and town. For DVA incidence rate versus Lyme incidence rate for both DMZs and towns, most of the correlation coefficients computed yearly were moderate to strong and all of the p-values were significant. A weak correlation was observed between deer population density and Lyme disease incidence rate by DMZ. The authors propose DVAs as a proxy for measuring the interaction between coexisting populations of humans and deer. The authors' study suggests that additional investigations of DVAs and their relationship to Lyme disease to further assess the utility of public health interventions are warranted.