Abstract. The geographic pattern of human risk for infection with Borrelia burgdorferi sensu stricto, the tick-borne pathogen that causes Lyme disease, was mapped for the eastern United States. The map is based on standardized field sampling in 304 sites of the density of Ixodes scapularis host-seeking nymphs infected with B. burgdorferi, which is closely associated with human infection risk. Risk factors for the presence and density of infected nymphs were used to model a continuous 8 km + 8 km resolution predictive surface of human risk, including confidence intervals for each pixel. Discontinuous Lyme disease risk foci were identified in the Northeast and upper Midwest, with a transitional zone including sites with uninfected I. scapularis populations. Given frequent under-and over-diagnoses of Lyme disease, this map could act as a tool to guide surveillance, control, and prevention efforts and act as a baseline for studies tracking the spread of infection.

The blacklegged tick, Ixodes scapularis, is of significant public health importance as a vector of Borrelia burgdorferi, the agent of Lyme borreliosis. The timing of seasonal activity of each immature I. scapularis life stage relative to the next is critical for the maintenance of B. burgdorferi because larvae must feed after an infected nymph to efficiently acquire the infection from reservoir hosts. Recent studies have shown that some strains of B. burgdorferi do not persist in the primary reservoir host for more than a few weeks, thereby shortening the window of opportunity between nymphal and larval feeding that sustains their enzootic maintenance. We tested the hypothesis that climate is predictive of geographic variation in the seasonal activity of I. scapularis, which in turn differentially influences the distribution of B. burgdorferi genotypes within the geographic range of I. scapularis. We analyzed the relationships between climate, seasonal activity of I. scapularis, and B. burgdorferi genotype frequency in 30 geographically diverse sites in the northeastern and midwestern United States. We found that the magnitude of the difference between summer and winter daily temperature maximums was positively correlated with the degree of seasonal synchrony of the two immature stages of I. scapularis. Genotyping revealed an enrichment of 16S-23S rRNA intergenic spacer restriction fragment length polymorphism sequence type 1 strains relative to others at sites with lower seasonal synchrony. We conclude that climate-associated variability in the timing of I. scapularis host seeking contributes to geographic heterogeneities in the frequencies of B. burgdorferi genotypes, with potential consequences for Lyme borreliosis morbidity.

Aim Ixodes scapularis is the most important vector of human tick-borne pathogens in the United States, which include the agents of Lyme disease, human babesiosis and human anaplasmosis, among others. The density of host-seeking I. scapularis nymphs is an important component of human risk for acquiring Borrelia burgdorferi, the aetiological agent of Lyme disease. In this study we used climate and field sampling data to generate a predictive map of the density of host-seeking I. scapularis nymphs that can be used by the public, physicians and public health agencies to assist with the diagnosis and reporting of disease, and to better target disease prevention and control efforts. Location Eastern United States of America.Methods We sampled host-seeking I. scapularis nymphs in 304 locations uniformly distributed east of the 100th meridian between 2004 and 2006. Between May and September, 1000 m 2 were drag sampled three to six times per site. We developed a zero-inflated negative binomial model to predict the density of host-seeking I. scapularis nymphs based on altitude, interpolated weather station and remotely sensed data. ResultsVariables that had the strongest relationship with nymphal density were altitude, monthly mean vapour pressure deficit and spatial autocorrelation. Forest fragmentation and soil texture were not predictive. The best-fit model identified two main foci -the north-east and upper Midwest -and predicted the presence and absence of I. scapularis nymphs with 82% accuracy, with 89% sensitivity and 82% specificity. Areas of concordance and discordance with previous studies were discussed. Areas with high predicted but low observed densities of host-seeking nymphs were identified as potential expansion fronts. Main conclusionsThis model is unique in its extensive and unbiased field sampling effort, allowing for an accurate delineation of the density of host-seeking I. scapularis nymphs, an important component of human risk of infection for B. burgdorferi and other I. scapularis-borne pathogens.

Long-term variations in the dynamics and intensity of sylvatic transmission of Trypanosoma cruzi were investigated around eight rural villages in the semiarid Argentine Chaco in 2002-2004 and compared to data collected locally in 1984-1991. Of 501 wild mammals from 13 identified species examined by xenodiagnosis, only 3 (7.9%) of 38 Didelphis albiventris opossums and 1 (1.1%) of 91 Conepatus chinga skunks were infected by T. cruzi. The period prevalence in opossums was fourfold lower in 2002-2004 than in 1984-1991 (32-36%). The infection prevalence of skunks also decreased five-fold from 4. 1-5.6% in 1984-1991 to 1.1% in 2002-2004. Infection in opossums increased with age and from summer to spring in both study periods. The force of infection per 100 opossum-months after weaning declined more than six-fold from 8. . The striking decline of T. cruzi infection in opossums and skunks occurred in parallel to community-wide insecticide spraying followed by selective sprays leading to very low densities of infected Triatoma infestans in domestic and peridomestic habitats since 1992; to massive deforestation around one of the villages or selective extraction of older trees, and apparent reductions in opossum abundance jointly with increases in foxes and skunks. These factors may underlie the dramatic decrease of T. cruzi infection in wild reservoir hosts.

In 2010 and 2011, field collections were undertaken to determine the geographic range of the lone star tick, Amblyomma americanum (L.), in Nebraska In addition, tick identifications from submissions by the general public dating to 1911 were examined. Consistent lone star tick identifications from extreme southeast Nebraska began in 1987. Specimens have been identified from 27 counties, making lone star ticks the second most frequently and second most widely reported tick in the state after Dermacentor variabilis (Say). Surveys conducted in 70 sites in 43 counties yielded 2,169 ticks of which 1,035 were lone star ticks. Lone star ticks were more frequent in the southeast portion of the state and ticks were found in nine counties from which there were no known submissions. Life stage peaks observed during the surveys corresponded with those observed from submissions. Other ticks, incidental to the study, were also collected. Woody plant expansion into the tallgrass prairie, white-tailed deer (Odocoileus virgianianus L.) and wild turkey (Meleagris gallopavo L.) population growth, and the increased frequency of milder winters may be facilitating lone star tick occurrence in the region. Further studies will assess lone star tick establishment and disease pathogen prevalence in the state.