Quantitative factors proposed to influence the prevalence of canine tick-borne disease agents in the United States.

The Companion Animal Parasite Council hosted a meeting to identify quantifiable factors that can influence the prevalence of tick-borne disease agents among dogs in North America. This report summarizes the approach used and the factors identified for further analysis with mathematical models of canine exposure to tick-borne pathogens.

County-level surveillance of white-tailed deer infestation by Ixodes scapularis and Dermacentor albipictus (Acari: Ixodidae) along the Illinois River.

From 1998 to 2003, 4,935 hunter-killed deer in northern and central Illinois were examined for ticks; 4,066 blacklegged ticks, Ixodes scapularis Say, and 6,530 winter ticks, Dermacentor albipictus (Packard) (Acari: Ixodidae), were collected. I. scapularis was the predominant tick species in the northern portion of the study area, with a decreasing north-to-south prevalence gradient. In contrast, D. albipictus was more common in the south with a decreasing south-to-north prevalence gradient. Compared with previous studies, the geographic range for both species expanded into the central portion of the Illinois River. Prevalence and intensity of both tick species were greater on bucks, and infested bucks were geographically more widespread than infested does and fawns. These findings indicate that blacklegged tick and winter tick distributions remain dynamic in the north central United States

Detection, characterization, and prediction of tick-borne disease foci.

Tick-borne disease (TBD) transmission foci need to be characterized in space and time, and are often discontinuous on both scales. An active TBD focus is dependent on the fulfillment of three conditions: tick survival, pathogen survival and opportunities for human exposure. The essentials for tick survival include food sources, reproduction, and protection from environmental extremes. The pathogen survival kit includes sufficient densities of ticks and suitable reservoir hosts, and opportunities for transmission between them in order to maintain infection. Opportunities for human exposure depend on sufficient number of encounters between ticks and humans. Because tick foci need to be described on a range of spatial and temporal resolutions, data for such characterization include a variety of surveillance data, field and laboratory experimental data, as well as results of statistical and mathematical analysis and modeling. The application of new tools from molecular biology, geographic information systems (GIS), and satellite imagery, in conjunction with appropriate analytical methods allow for detection of unknown foci and prediction of new ones. A long-term multi-scale study of Ixodes scapularis and Lyme disease in the north-central U. S. is reviewed. Diverse surveillance methods of ticks, rodents, deer, canids and humans were coupled with environmental characterization in situ to create a habitat profile for Lyme disease ticks. Incorporating various digitized databases, a statistical model was used to develop a risk map for tick distribution in the region. The process of introduction and establishment of new tick foci along the Illinois River is described in relation to the known tick distribution and predictions of invasion based on the risk model.

Predicting the risk of Lyme disease: habitat suitability for Ixodes scapularis in the north central United States.

The distribution and abundance of Ixodes scapularis were studied in Wisconsin, northern Illinois, and portions of the Upper Peninsula of Michigan by inspecting small mammals for ticks and by collecting questing ticks at 138 locations in state parks and natural areas. Environmental data were gathered at a local level (i.e., micro and meso levels), and a geographic information system (GIS) was used with several digitized coverages of environmental data to create a habitat profile for each site and a grid map for Wisconsin and Illinois. Results showed that the presence and abundance of I. scapularis varied, even when the host population was adequate. Tick presence was positively associated with deciduous, dry to mesic forests and alfisol-type soils of sandy or loam-sand textures overlying sedimentary rock. Tick absence was associated with grasslands, conifer forests, wet to wet/mesic forests, acidic soils of low fertility and a clay soil texture, and Precambrian bedrock. We performed a discriminant analysis to determine environmental differences between positive and negative tick sites and derived a regression equation to examine the probability of I. scapularis presence per grid. Both analyses indicated that soil order and land cover were the dominant contributors to tick presence. We then constructed a risk map indicating suitable habitats within areas where I. scapularis is already established. The risk map also shows areas of high probability the tick will become established if introduced. Thus, this risk analysis has both explanatory power and predictive capability.