Occurrence of ixodes scapularis and borrelia burgdorferi in the fragmented landscapes of east-central and northeast Illinois

The distribution of Ixodes scapularis and Borrelia burgdorferi has continued expanding in Illinois over the past twenty years. However, the extent to which this tick vector and etiologic agent of Lyme disease has spread is not well known. In east-central Illinois (ECIL), I evaluated habitat diversity and temporal changes of I. scapularis occurrence and B. burgdorferi infection within a natural area in Piatt County, Illinois. In northeast Illinois (NEIL), I assessed the geographic distribution and abundance of I. scapularis in forest patches of 32 public-access forest preserves in Cook, DuPage, Lake, and McHenry counties. In ECIL, small mammals were trapped and attached ticks were collected in young forest, prairie, old forest, and flood plain sites from 2005 ??? 2009. Small mammal diversity and abundance were compared. Collected ticks were identified to species level based on morphology, and identification was confirmed molecularly. Prevalence of I. scapularis (% mammals infested), mean intensity (I. scapularis per infested mammal), and relative density (I. scapularis per mammal trapped) were calculated. Multiple I. scapularis larvae found on a single mammal were pooled for testing; whereas, I. scapularis nymphs were tested individually for B. burgdorferi infection using polymerase chain reaction (PCR). Ixodes scapularis were most abundant in the young forest and prairie sites. The prairie had the highest diversity of small mammal hosts. Out of 2,446 trapped small mammals, 388 were infested with I. scapularis. Prevalence, mean intensity, and relative density of I. scapularis and prevalence of B. burgdorferi infection were highest for the prairie and young forest sites. The overall B. burgdorferi infection of I. scapularis in the natural area was 14% (56 / 388). In NEIL, timed dragging surveys were conducted from May to October 2008 and April to October 2009. A total of 602 I. scapularis of all three life stages (larvae, nymphs, and adults) were collected from 17 of the 32 sites. The highest abundances of I. scapularis were found at coastal forested sites near Lake Michigan, and I. scapularis appears to be widely distributed throughout the counties of Cook, DuPage, and Lake where suitable habitat is available. The distribution of I. scapularis is encroaching upon developed areas, increasing the risk for human exposure to Lyme disease. This study provides baseline data for further evaluation of emerging Lyme disease foci in Illinois. Habitats and reservoir hosts that were previously overlooked may be suitable for I. scapularis and B. burgdorferi establishment in a dynamic fragmented landscape. This study reveals mechanisms associated with wildlife ??? vector ??? pathogen interactions that could influence disease emergence and exposure, and it emphasizes the need to increase research efforts and public awareness concerning the occurrence of I. scapularis and the prevalence of B. burgdorferi in Illinois