County-Scale Distribution of Ixodes scapularis and Ixodes pacificus (Acari: Ixodidae) in the Continental United States

The blacklegged tick, Ixodes scapularis Say, is the primary vector to humans in the eastern United States of the Lyme disease spirochete Borrelia burgdorferi, as well as causative agents of anaplasmosis and babesiosis. Its close relative in the far western United States, the western blacklegged tick Ixodes pacificus Cooley and Kohls, is the primary vector to humans in that region of the Lyme disease and anaplasmosis agents. Since 1991, when standardized surveillance and reporting began, Lyme disease case counts have increased steadily in number and in geographical distribution in the eastern United States. Similar trends have been observed for anaplasmosis and babesiosis. To better understand the changing landscape of risk of human exposure to disease agents transmitted by I. scapularis and I. pacificus, and to document changes in their recorded distribution over the past two decades, we updated the distribution of these species from a map published in 1998. The presence of I. scapularis has now been documented from 1,420 (45.7%) of the 3,110 continental United States counties, as compared with 111 (3.6%) counties for I. pacificus. Combined, these vectors of B. burgdorferi and other disease agents now have been identified in a total of 1,531 (49.2%) counties spread across 43 states. This marks a 44.7% increase in the number of counties that have recorded the presence of these ticks since the previous map was presented in 1998, when 1,058 counties in 41 states reported the tic...

Source: Journal of Medical Entomology - March 8, 2016 Category: Biology Authors: Eisen, R. J., Eisen, L., Beard, C. B. Tags: Sampling, Distribution, Dispersal Source Type: research