Location: Arthropod-borne Animal Diseases Research
2015 Annual Report
Objectives
Objective 1: Perform risk assessment of bacterial pathogen transmission by house flies.
Sub-objective 1.A: Develop more effective larval control techniques by understanding the role of microbes in larval development and fitness.
Sub-objective 1.B: Evaluate the role of fly-bacteria and bacteria-bacteria interactions in house fly pathogen transmission.
Objective 2: Determine biological characteristics of mosquito vectors influencing animal health in a changing climate.
Sub-objective 2.A: Model mosquito ecological niches and impact of climate change.
Sub-objective 2.B: Characterize the biology of discrete mosquito populations.
Objective 3: Develop methods to reduce biting midge transmission of animal pathogens.
Sub-objective 3.A: Identify and characterize the salivary protein components of Culicoides sonorensis.
Sub-objective 3.B: Identify potential Culicoides vectors of epizootic hemorrhagic disease and bluetongue.
Sub-objective 3.C: Determine breeding site characteristics of Culicoides spp..
Sub-objective 3.D: Evaluate efficacy of candidate pesticides against C. sonorensis.
Approach
An extremely small percentage of insect species transmit disease-causing pathogens to animals and humans. Specific biological and behavioral characteristics allow these vector insect species to be efficient means of pathogen propagation and transmission; however these same characteristics may be targeted by control measures to limit pathogen spread or disease vector abundance. The common purpose of these projects is to understand key components of the host-pathogen-vector cycle to reduce or prevent pathogen transmission by the most common disease vectors: house flies, mosquitoes, and biting midges (Fig. 1). House flies associate with bacteria-rich environments due to the nutritional requirements of their larvae. This research defines the role of bacteria in fly development, bacterial persistence during microbe and insect interactions, and pathogen dissemination. Natural selection for increased Culex tarsalis mosquito fitness for various habitats and animal hosts has left genetic markers (single nucleotide polymorphisms) throughout the genome. These markers can be associated with traits and used to predict regional entomological risk in a changing climate throughout the mosquito’s large geographic range. The identification of biting midges or Culicoides saliva components that facilitate pathogen transmission will lead to improved transmission and pathogenesis models. This information will enhance development of vaccines and other countermeasures to reduce disease transmission. Lastly, not all Culicoides are competent vectors and this study will determine vector species and their habitats to help estimate risk in specific geographic regions. This plan aims to limit pathogen transmission by targeting the connections between hosts, vectors, and their environments via the insects’ unique characteristics using novel disease control methods.
Progress Report
This project has resulted in developing integrated approaches to protect animals and people from vector-borne pathogens. Some advancements and products for midges, mosquitoes, and house flies are:
A major allergen found in the saliva of C. sonorensis is called D7 protein. The D7 gene has been successfully cloned into a baculovirus protein expression vector. Native D7 protein is being produced in cell cultures and purification methods are being optimized.
(1 & 2) Four catalogs of expressed genes (transcriptomes) for adult house flies were constructed in collaboration with Kansas State University and Clemson University, in order to determine the adult fly genetic response after feeding on bacterial pathogens (Salmonella and Staphylococcus).
The first account of RNA-interference in the biting midge, Culicoides sonorensis, was published, and ARS and Kansas State University scientists are using this tool to understand the function of genes associated with vector competence for orbiviruses.
The annotated reference transcriptome for the biting midge, Culicoides sonorensis, was released in AgData Commons at the NAL (DOI pending).
Bacterial species associated with manure, larvae, pupae and adults of wild-caught house flies were cultured and identified in order to determine the trans-stadial carriage of bacteria in the natural environment.
Bacterial species found in the gut and surface of adult female flies were compared to those found on fresh-deposited eggs and it was determined that bacteria are transmitted during the egg-laying (oviposition) process in house flies.
(3) The mosquito, Culex tarsalis, has a geographic range in the Continental United States east of the Mississippi from Canada to Mexico. However, the mosquito movement with that range is limited by geographic and environmental barriers, which define six genetic subpopulations within the species distribution. This study determined the extent of the geographic ranges.
(4 & 5) Culicoides populations and their associations with specific breeding habitats was studied at multiple sites that differ in their animal use patterns (beef cattle, dairy units, farmed deer, and bison and cattle grazed prairie). The distribution of known and putative disease vectors in the landscape has been partially characterized and is being evaluated for relationships with habitat type, soil characteristics, animal use patterns, microbial populations, and variation in seasonal rainfall. Data continued to be collected through 2015 on these characteristics as part of developing a long term data set. Research at the beef cattle, dairy units and the captive cervid farm will be concluded in late 2015
(6) Evaluation of spot-on membrane systems for Culicoides control was conducted in 2015, data input and analysis will continue into 2016.
Accomplishments
1. Annotated catalog of biting midge genes. Female biting midges transmit viruses that impact our nation’s livestock and wildlife. In FY 14, ARS scientists in Manhattan, Kansas, in collaboration with Clemson University, generated and published the first catalog of expressed genes for female midges under several feeding conditions. The annotated version of this catalog, where the genes are named and categorized by process, was released in FY 15 on the Ag Data Commons site at the National Agriculture Library. This annotated catalog can now be accessed by collaborators and stakeholders and utilized in studies of midge biology, function and control.
2. House fly interactions with bacteria. House flies associate with bacteria-rich environments across their life history. ARS scientists in Manhattan, KS characterized bacteria species that are associated with the eggs, larvae and adults of both colony-reared and wild-caught house flies. These studies can help in understanding the importance of bacteria in fly development which can inform new control and management strategies.
Review Publications
Nayduch, D., Joyner, C. 2013. Expression of lysozyme in the life history of the house fly (Musca domestica L.). Journal of Medical Entomology. 50: 847-852.
Nemeth, N., Ruder, M.G., Gerhold, R., Brown, J., Munk, B., Oesterle, P., Kubiski, S., Keel, K. 2013. Demodectic Mange, Dermatophilosis, and other parasitic and bacterial dermatologic diseases in free-ranging white-tailed deer (Odocoileus virginianus) in the United States from 1975-2012. Veterinary Pathology. 00(0):1-8.
Reeves, W.K., Miller, M.M. 2013. Culicoides sonorensis (Diptera: Ceratopogonidae) is not a competent vector of Cache Valley virus (family Bunyaviridae, genus Orthobunyavirus). Archives of Virology. 158:2175-2177.
Schumm, P.R., Scoglio, C.M., Zhang, Q., Balcan, D. 2015. Global epidemic invasion thresholds in directed cattle subpopulation networks having source, sink, and transit nodes. Journal of Theoretical Biology. 367: 203-221. doi:10.1016/j.jtbi.2014.12.007.
Nayduch, D., Lee, M., Saski, C. 2014. Gene discovery and differential expression analysis of humoral immune response elements in female Culicoides sonorensis (Diptera: Ceratopogonidae). Parasites & Vectors. 7:388. doi:10.1186/1756-3305-7-388.
