The landscape ecology of Lyme disease was studied in 1989 on 67 residences in an endemic area of Armonk, Westchester County, a northern suburb of New York City. Four main habitat types were defined, and each property was surveyed for immature and adult lxodes dammini ticks; 98.6% of 1,790 ticks collected were I. dammini. Overall, 67.3% were collected from woods, 21.6% from ecotone (unmaintained edge), 9.1% from ornamental vegetation, and 2% from lawns. Larval ticks were concentrated in woods, but nymphs and adults were widely dispersed in all habitats. Tick abundance was positively correlated with property size. Larger properties (greater than or equal to 0.5 acre) were more likely to have woodlots and, hence, more ticks. Dark-field and direct fluorescent microscopic examination of tick midgut tissues revealed that 29.6% of nymphs and 49.7% of adults were infected with Borrelia burgdorferi. Infected nymphs and adults were found on 36% and 60% of properties, respectively. These data indicate that the abundance of ticks capable of transmitting Lyme disease spirochetes is related to landscape features of the suburban residential environment.
The relationship between the attachment duration of adult female Ixodes dammini and the transmission of Borrelia burgdorferi was studied. Sixteen rabbits were exposed to spirochete-infected female ticks for specified intervals. All five rabbits exposed to ticks that fed to repletion (greater than 120 h) became infected, as did two of three exposed for 48 h. In contrast, five rabbits exposed to a cumulative total of 53 infected female I. dammini for 36 h failed to become infected, as did three rabbits exposed for 24 h. A needle aspirate method facilitated the isolation of spirochetes from host skin.
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