Recipient Organization
VIRGINIA POLYTECHNIC INSTITUTE
(N/A)
BLACKSBURG,VA 24061
Performing Department
Entomology
Non Technical Summary
Problem statement: Vector-borne diseases are a growing concern for public health in the USA and across the world [1, 2]. Mosquito-borne pathogens have caused devastating epidemics such as Zika and chikungunya viruses [3]. Tick-borne diseases are increasing as populations of tick-vectors surge [4, 5]. Invasive species of arthropod are frequently introduced to new regions, along with the pathogens that they transmit. In order to limit the burden of disease, the ecology of emerging infectious disease (definition) is essential to understanding the past and predicting the future spread of disease, and how their transmission is facilitated and influenced by environmental and anthropogenic change.Relevance: Vector-borne diseases (VBD) have a massive economic impact on the U.S. healthcare economy. For example Lyme disease [LD], with 300,000 estimated cases a year, costs up to $1.3 billion [6]. Virginia (as with other States) is experiencing an increase in VBD. The CDC reported 1041 LD cases in Virginia in 2017 and classify the state as 'high-incidence'; there were over 100 confirmed cases per 100,000 persons that year in the New River Valley, which is a hot-spot for LD within the Commonwealth. In addition, other tick- and mosquito-borne pathogens are threatening the region [5, 7]. There have been 8 cases of La Crosse virus (LACV) in VA, and 152 cases of West Nile virus (WNV), both mosquito-borne neuro-invasive diseases, reported to CDC over the last decade [8, 9].One Health is the consideration that human, animal and environmental health are intertwined. The proposed research has an immense One Health importance with both animal and public health affected by vectored disease. There is relevance for agricultural sectors (for example, an exotic tick species from Asia infests livestock and wildlife, and has already been found to transmit Theileria parasites to cattle [10]), and companion animals (for example, leishmaniasis, bartonellosis and anaplasmosis affects dogs or cats) [11, 12]. Vector-borne disease research is also pertinent to addressing the environmental component of One Health, for example forest clearance, land-use changes and loss of biodiversity can heighten the risk of VBD to rural and agricultural communities, as well as leading to spillover and spillback of pathogens between wildlife and domestic populations [13, 14]. Additionally, vector-borne illnesses pose a threat to the military, forestry and farm workers, rural communities, as well as tourists spending time outdoors [15-19]. Studying aspects of the key vector-borne disease risks in Virginia and further afield - the vector ecology, pathogen prevalence, and influences of our changing environments - is important to ensuring healthier communities and spaces for residents, visitors and livestock. Knowing the ecology of novel pathogens and vector species that may be detected in the region is vital to protect against the impact of invasion, taking steps towards disease prevention, or controlling damaging vector introductions. Approach: We will examine the ecology of arthropod vector species, sampling at multiple U.S. locations across seasons to determine infection prevalence, the influence of habitat, ability to transmit pathogens, and factors underlying co-infection status with multiple pathogens.
Animal Health Component
80%
Research Effort Categories
Basic
20%
Applied
80%
Developmental
(N/A)
Goals / Objectives
The overarching goal of the project is to provide improved understanding of vector-borne disease ecology, the transmission of arthropod-vectored pathogens, and factors influencing the emergence of novel infectious disease. This proposal includes seeking to fulfill an urgent need to establish an understanding of vector-borne pathogens in the SW Virginia region.This will be achieved by the following three Specific Aims:Objective 1) Establish a Baseline assessment of vectors in SWVirginia, monitoring over a latitudinal and ecological gradient, including recreational habitat.Objective 2) Determine pathogen infection rates in collected arthropod vectorsObjective 3) Determine any pertinent landscape influences on vector abundance and pathogen prevalence
Project Methods
Methods/Procedures Objective 1) Establish a baseline assessment of vector species. We will sample at multiple locations radiating from Blacksburg, VA including a SW-NE gradient along I-81 highway (East of the Appalachian Mountains). At each location,transects in each of three different habitats (forest, farm pasture, urban parks) will be used to conduct monthly surveys. For mosquitoes, BG-Sentinel or CDC light traps will be employed overnight during summer months. For ticks this will consist of drag sweeps during May to November when nymphal and adult stages are expected. Sweeps, which involve walking a 1x1m cloth over vegetation, and assessing the catch every 10m, and tick densitycalculated. This is an effective way to collect ticks from the wild; ticks will be removed (kept in live jars to preserve viral RNA until processing), identified to species level, and life-stage noted. Molecular confirmation of species will be conducted on a sub-set of vectors using DNA/RNA extraction and PCR amplification targeting pathogen genes. A population density estimate will be made per site for each species and seasonal peaks indicated. An limit of 40 individuals per site (collected from a variety of spots within a site) will be screened for pathogens using established assay methods (see objective 2). The threshold of 40 individuals has been set in order to keep the cost of testing manageable; deemed suitable by VT SAIG. Years 1 & 2 (Summer - Fall) will establish a baseline. Years 3-5 (Spring - Fall) will assess the same sites, observing temporal changes in tick and vertebrate populations, and pathogen prevalence. Required sample numbers will be determined using G*power analysis.Objective 2) Pathogen screening and analysis. The technical approach lies in efficiently detecting emerging pathogens, including La Crosse virus, West Nile virus, Borrelia spp.; Anaplasma phagocytophilum, Babesia microti, Ehrlichia spp., Heartland and POWV viruses. The latter are key emerging pathogens of concern connected to an influx of I. scapularis and H. longicornis into Virginia. Both tick-borne B. burgdorferi infections and mosquito-borne LaCV and WNV have previously been detected in the arthropod vector, and clinical cases arisen, in the Appalachian regions. Rapid and accurate ways of testing for the presence of serious pathogens are vital. Collected arthropods will be homogenized (using a tissuelyser machine), and either inoculated onto cell line for detection of virus, or used to extract nucleic acid for qPCR screening, to screen for bacterial or viral pathogens. An aliquot will also be kept frozen at -70°C to enable viral isolation endeavors. The PI has access to (non-infectious) viral RNA or pathogen DNA that can be used in the analytic validation of molecular assays. For cost-effective analysis, pooling of vector specimens (into groups of up to 25 from the same location/date/species), as long as it is not shown to affect the sensitivity of the assay nor limit of detection, is a good way to manage sample numbers for high-input screening, particularly as many vector-borne agents are low-prevalence pathogensthat we might not detect initially. Use of a multi-pathogen assay will engage a cutting-edge tool essential for effective rapid testing of ticks in the vicinity.Objective 3) Predictive modeling will be conducted to determine the pertinent features of landscape, and ecological influences on vector-pathogen prevalence. Land-use coverage and elevation maps are available (USGS.gov), and reported CDC data on local human case incidence can be integrated into spatial models to understand disease spread. At each surveyed location, geographical co-ordinates will be taken and used to construct geographical information system [GIS] spatial maps of vector distribution and abundance, as well as pathogen carriage rates. At sub-sites, local weather stations or Hobo loggers will be used to monitor temperature and humidity, and an assessment of habitat characteristics and vertebrate presence noted (camera trapping &/or point surveys). Site factors will also be used, in addition to climatic variables generated by event loggers, to consider determinants of vector and pathogen predictions; this would include distance to nearest urban settlement and to roads. Finding climate to be a significant predictor of vector presence would indicate the extent to which climate change might play a role in associated VBD. Risk hot-spots (based on peaks of density and pathogen prevalence) can be produced. Such 'heat-maps' can serve in the future as the basis for prioritizing vector control, and will be disseminated to inform public health institute of results.Statistical analysis: Infected rates for each pathogen will be calculated as a percentage of all individuals of that vector species screened for that pathogen. Further analyses appropriate for the type of data produced in the study include logistic regression, correlation, chi-squared tests, and power analysis. Analysis choice and experimental design have been discussed with Virginia Tech's Statistical Applications and Innovations Group (SAIG), feeding into the choice of sample quantity adequate to detect pathogen prevalence