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This project will examine interactions that disperse and sustain tick populations and that directly and indirectly effect human and animal health. By defining these interactions, this project seeks to discover new methods to measure and predict risks associated with tick parasitism, and to define new approaches to tick population suppression.
The specific objectives include: 1. Determine the influence of climate on the genetic diversity and spatial-temporal dynamics of tick populations, and 2. Determine the role of feral and exotic vertebrates on tick population maintenance and dispersal on Texas landscapes and their importance in emerging and re-emerging tick-borne diseases. <P>We hypothesize under objective 2 that feral swine have become an important component of the maintenance and dispersal of ticks in Texas and that because of this relationship feral swine are likely to be serving as a reservoir or maintenance host of tickborne zoonotic pathogens. We expect that per animal tick loads, both the numbers of tick species parasitizing the host and numbers found per species, and pathogen prevalence associated with feral swine will vary across Texas landscapes due to the characteristics of the xeric-to-mesic habitat types.
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We intend to: 1) establish a record of tick species associated with feral pigs in Texas; 2) compare the seasonal and temporal occurrence of tick species found in association with feral pigs to current records of these tick species in Texas; 3) compare the tick assemblages and their seasonality on feral pigs in two different eco-regions of Texas; and 4) assess the prevalence of four genera of tickborne bacteria in the feral pig populations of these two eco-regions. If feral pigs are shown to play a role in the maintenance of zoonotic disease pathogens for livestock, companion animals, and/or humans, the economic and health impacts of these animals will need to be reassessed.
NON-TECHNICAL SUMMARY: More than 20 species of ixodid ticks are resident to Texas and pose economic and health risks to livestock, wildlife, companion animals and humans. Direct livestock production losses accrue from tick parasitism through blood-loss, irritation, poor rates of gain, weight-loss, loss of body condition, and diminished reproductive capacity. Parasitism of range cattle by the lone star tick, Amblyomma americanum, and the Gulf Coast tick, A. maculatum, alone is estimated to exceed $2l8 million in annual direct production losses. Indirect costs for animal handling and treatment further increase production costs. Transmission of tick borne pathogens resulting in diseases of livestock such as bovine babesiosis and anaplasmosis , of companion animals such as canine babesiosis and hepatozoonsis, or of humans including borreliosis (Lyme), rickettsiosis, ehrlichiosis, and tularemia are also associated with health risks and costs of testing, diagnosis and treatment. Recent decades have revealed the expansion and contraction of some tick species, the introduction of new species, and the re-emergence of old species previously held in check by regulatory programs. Ecological changes resulting from drought cycles and the expansion of feral and exotic animals may explain changes in tick distribution and abundance and may be valuable in defining new methods to assess risk of tick parasitism and tick-borne disease. We expect the impact of these investigations to improve risk assessment for several important species of ticks and of the disease pathogens maintained in nature; futher, we expect these investigations to clearly define how we can use meterological factors to measure and predict changes in tick populations and how to best integrate tick control tactics for optimal intervention.
<P>Meteorological elements such as soil temperature, soil moisture, dewpoint, precipitation, minimum and maximum air temperature, and drought levels are potential predictors of survival and genetic diversity in tick populations. We hypothesize under objective 1 that meteorological factors regulate the inland population expansion and contraction of Gulf Coast ticks in Texas. This hypothesis will be tested by defining the spatial and temporal characteristics of Gulf Coast tick population change across Texas counties and determining which meteorological factors best describe tick population expansion and contraction. We expect this investigation to provide predictive models that effectively describe these changes and provide a new means of risk assessment for use by livestock owners.
<P>APPROACH: Archived tick collection records for Texas 1992-2008 will be used to compare Gulf Coast tick population changes measured at cattle auction facilities in 90 inland counties from central and northeast Texas to those measured along Gulf Coast counties. Meteorological data will be obtained from several sources. Precipitation and max and min temperature will be acquired from the Center for Natural Resource Information Technology of Texas A&M University. Soil temperature and soil moisture will be obtained from the National Oceanic and Atmospheric Administration. Drought indices will be obtained from the Texas Weather Connection of the Spatial Sciences Laboratory of Texas A&M University. Lastly, dewpoint data will be collected from PRISM Group of Oregon State University. Once collected, these data will be analyzed using the raster calculator feature on ESRI's ArcMap program. Meteorological data will be organized into periods that coincide with the seasonal activity of each developmental stage. Progressive analyses of these groupings will test whether meteorological factors during individual immature stages effect population expansion and contraction of adult ticks. Predictive equations for the number of tick collections will be analyzed using several SAS procedures(SAS, Inc., Cary, N.C.). Adult ticks collected throughout the southern region will be examined to determine patterns of genetic variation in the 16s rDNA gene. Feral pigs will be trapped from study sites in different ecoregions of Texas throughout the year to estimate tick loads and the prevalence of tick borne pathogens in local pig populations. Prevalence of tick species by location, host gender and age-class, and season will be analyzed and tabulated to provide an assessment of the role of feral pigs as a maintenance and dispersal host for ticks on Texas landscapes. Sero-prevalence of tick borne pathogens will be assessed using dot-blot and western-blot analyses. Evidence of DNA of the zoonotic bacteria Rickettsia, Borrelia, Ehrlichia, and Anaplasma will be determined by standard extraction, amplification and sequencing techniques. Prevalence of positive blood samples by location, host age-class and season will provide evidence feral pigs maintain tick-borne pathogens.