Academic journal article Bulletin of the World Health Organization

Risk of Lyme Disease: Perceptions of Residents of a Lone Star Tick-Infested Community. (Research)

Academic journal article Bulletin of the World Health Organization

Risk of Lyme Disease: Perceptions of Residents of a Lone Star Tick-Infested Community. (Research)

Article excerpt

Voir page 923 le resume en francais. En la pagina 924 figura un resumen en espanol.

Introduction

The health burden of Lyme disease (an infection caused by Borrelia burgdorferi) in the eastern US is largely due to its tendency to occur in focal outbreaks. Indeed, the first 51 human infections that were recognized occurred in people residing in or near a place called Old Lyme (in coastal Connecticut), and involved 1 in 10 people living along only four roads (1). Similar clustered cases soon became evident in other sites in north-eastern USA. The seroprevalence ranges from 5% to 25% in communities located on Fire Island (on Long Island, New York), on Great Island (on Cape Cod in Massachusetts), in Ipswich (north of Boston, Massachusetts) and on Block Island (off the Rhode Island coast) (2-5). Representative incidences of Lyme disease in north-eastern USA during the two-year phase-III Lyme disease vaccine trials were estimated at 1.0-1.5% using stringent surveillance criteria (6, 7), but certain sites recorded a higher incidence (1.9-2.1%) (8).

In the USA, cases of Lyme disease appear to cluster only as far south as Maryland, although virtually all states have reported some cases. In a summer camp in Kent County (in the north-eastern part of Maryland), for example, the sera of 16% of 51 employees reacted against B. burgdorferi antigen (9). In contrast, no such evidence of infection was discovered in a group of outdoor workers who had intense exposure to ticks on Assateague Island (in the south-eastern corner of Maryland) (10). In 1993, however, we learned of a residential site in central Maryland where the risk of Lyme disease appeared to be as intense as in the north-east of the state. The residents of this community, which included an experienced epidemiologist, provided a survey-based informal report that suggested a 12% incidence for physician-diagnosed Lyme disease during both the 1991 and 1992 summers. To the best of our knowledge, this site would represent the southern-most focus of intensely prevalent Lyme disease in the USA.

It may be that the clustered pattern of intense risk of Lyme disease that burdens the residents of many communities located in the north-eastern USA extends south to central Maryland. In such southerly sites, ticks other than those serving as vectors for Lyme disease (Ixodes spp.) more commonly infest people. Comprehensive epidemiological studies have not been carried out to determine whether dog ticks (Dermacentor variabilis) or Lone Star ticks (Amblyomma americanum) are associated with the risk of Lyme disease. To evaluate this possibility, we investigated the local risk of infection in an island community in central Maryland. In particular, we recorded the incidence of disease episodes reported by residents of the study site, estimated the frequency of human infection by a prospective serosurvey, and evaluated the risk by entomological means.

Materials and methods

Study site

Gibson Island in Maryland was chosen for this analysis because its residents anecdotally reported a disproportionate number of physician-diagnosed cases of Lyme disease and their intense annoyance due to ticks. The island site covers 380 ha and is linked to the western shore of Chesapeake Bay by a causeway, which is located about 25 km south-east of Baltimore. A total of 335 year-round residents lived there during the 1990 US census. The community comprises residents of higher than average socioeconomic and educational status. The oak forest that dominates the island is broken by several meadows. A dense understory of plants is mainly made up of kudzu (Pueralia thumbergiana) and bitter-sweet (Celastrus scandens). White-tailed deer (Odocoileus virginianus) are numerous; about 80 deer were identified by an aerial survey conducted in 1994 by the Maryland Department of Natural Resources. Other abundant animals include white-footed mice (Peromyscus leucopus), cottontail rabbits (Sylvilagus floridanus), grey squirrels (Sciurus carolinensis), and opossums (Didelphis marsupialis). …

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