title: Clustering of host-seeking nymphal deer ticks (Ixodes dammini) infected by Lyme disease spirochetes (Borrelia burgdorferi).
abstract: In areas where the agent of Lyme disease is intensely enzootic, the mouse reservoirs may be universally infected. Because a large proportion of the vector tick population appears to feed upon these hosts, the prevalence of infection in the vectors should approach 100%. However, infection in host-seeking nymphal ticks in nature rarely exceeds 40%. To help reconcile this apparent paradox, we examined whether estimates of prevalence might differ if we did not assume that infected ticks are randomly or uniformly distributed within a site. Nymphal Ixodes dammini were collected by dragging a series of 10-meter replicates within an intensely enzootic site. Estimates of the prevalence of spirochetal infection, based upon the monthly means of individual 10-meter collections, were then compared with estimates derived by pooling all samples. Host-seeking ticks tended to cluster. The Lyme disease spirochete was present in 15.6% of 469 pooled ticks. When the prevalence estimate was based solely on ticks in clusters that contained one or more infected ticks, however, at least 50% of the ticks were infected. We conclude that nymphal deer ticks infected by Lyme disease spirochetes tend to aggregate spatially in nature, and that prevalence estimates based upon a mean value for pools may be misleading.
authors.affiliation: Department of Tropical Public Health, School of Public Health, Harvard University, Boston, Massachusetts.
authors.forename: S R
authors.initials: SR
authors.lastname: Telford
authors.forename: S S
authors.initials: SS
authors.lastname: Urioste
authors.forename: A
authors.initials: A
authors.lastname: Spielman
mesh_terms: D000818:Animals; D001096:Arachnid Vectors / Q000302:isolation & purification / Q000382:microbiology*; D015748:Borrelia burgdorferi Group / Q000302:isolation & purification*; D016000:Cluster Analysis; D003198:Computer Simulation; D003670:Deer; D008954:Models, Biological; D013987:Ticks / Q000302:isolation & purification / Q000382:microbiology*