Location: Arthropod-borne Animal Diseases Research2016 Annual Report
1a. Objectives (from AD-416):
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.
1b. Approach (from AD-416):
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.
3. 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: Objective 1A, eight catalogs of expressed genes (transcriptomes) for larvae of flies of veterinary importance (house fly, stable fly, horn fly, face fly; two replicates each) were constructed in collaboration with USDA-ARS, Kerrville, TX and Clemson University. Comparative analysis will reveal the way they differentially utilize manure as a developmental substrate. Objective 3A, the first account of double-knockdown of gene expression in the biting midge, Culicoides sonorensis, a collaborative effort between ARS and Kansas State University scientists, showed that this tool can be used to manipulate genes, and phenotypes, in these important disease vectors. Objective 1B, in collaboration between ARS and Kansas State University, it was shown that male and female house flies differentially acquire and harbor bacteria from manure. Female flies both obtain and accumulate more bacteria then males, and this finding may help in modeling vector potential and risk of disease spread. Objective 2A, the mosquito, Aedes vexans, has a geographic range spanning the entire Continental United States. Within this range, mosquito movement is not restricted by plant types or environmental factors and no well-defined populations were identified by geographic and environmental barriers. This surprising result was supported by poor separation of past populations identified by phylogenetic analysis. Objective 3B, 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 2018 on these characteristics as part of developing a long-term data set. Sampling frequency at the beef cattle, dairy units and the captive cervid farm has been reduced because short-term goals have been met and long-term studies at these sites do not require such intensive effort. Evaluation of the relationships between Culicoides distribution in the environment and the suitability for development by C. sonorensis to site-specific soil chemistry and microbiomes was initiated in 2016 and will continue through 2017. Objective 3D, evaluation of spot-on membrane systems for Culicoides control has been completed and data input is currently underway. Objective 3A, the major Culicoides salivary allergen D7 has been cloned into a baculovirus expression system and the late trypsin salivary protein has been cloned into an E. coli expression system. Proteins have been expressed and purification methods are being optimized.
1. Ability for United States mosquitoes to transmit exotic pathogens. Can United States mosquito species such as Culex quinquefacsiatus transmit Japanese Encephalitis virus? Japanese encephalitis virus (JEV) is a flavivirus that is transmitted by Culex genera mosquitoes in tropical and subtropical regions of Asia. The endemic transmission cycle involves domestic pigs and avian species that serve as amplification hosts; humans are incidental hosts that cannot develop a high-titer viremia sufficient for mosquito infection. In multiple Asian countries, human populations can suffer from severe neurological problems. The potential introduction of JEV into North America would be a major threat to human and animal health. In this study, field-collected Cx. quinquefasciatus from Valdosta, Georgia, were tested for their susceptibility to JEV and their potential to transmit the virus. These results demonstrate that North American Cx. quinquefasciatus are susceptible to JEV infection suggesting the United States may be susceptible JEV transmission if the virus were to be introduced.
2. Annotated catalog of biting midge genes associated with EHDV infection. Female biting midges transmit viruses that impact our nation’s livestock and wildlife. In FY 16, ARS scientists in Manhattan, Kansas, in collaboration with Clemson University, generated the first catalog of expressed genes associated with epizootic hemorrhagic disease virus infection in female midges. This catalog can be used by collaborators and stakeholders in identifying new targets for blocking virus transmission by midges and understanding the genetic components of midge-virus interactions.
3. Dose-dependent fate of bacteria in house flies. House flies ingest and harbor bacteria, and serve as potential vectors of disease. The fate of bacteria in flies, including survival and persistence, is directly related to their transmission potential. ARS scientists in Manhattan, Kansas described for the first time a dose-dependent effect on the survival of E. coli in house flies. This finding can help better define the risk flies pose in harboring and transmitting bacterial pathogens to livestock and animals.
4. Trans-stadial carriage of bacteria from manure through development of house flies. ARS scientists in Manhattan Kansas demonstrated that bacteria ingested by house fly larvae can survive metamorphosis and colonize adult house flies, bolstering the potential for microbes to be disseminated by flies from managed manure.
5. Significant Activities that Support Special Target Populations:
Deer farmer workshops on biting midge control to prevent disease transmission. The United States Department of Agriculture – Agricultural Research Service (USDA-ARS) teamed with the North American Deer Farmer’s association (NADeFA) to help captive deer producers combat disease transmitting midges that are devastating their industry. The captive deer industry is a five billion dollar industry in the United States and is responsible for saving many small family farms, in addition to, providing rural jobs in America. In a little more than a year, USDA scientists have written six review articles for the NADeFA journals that translate the government’s ongoing biting midge research to field applicable practices for preventing and mitigating epizootic hemorrhagic disease (EHD) and bluetongue (BT), the most devastating diseases to the industry. Furthermore, ARS scientists have given seven workshops in four states each hosted by the local state association. Each workshop consists of 1.5 hours of basic science on midges, EHD, and deer biology to provide a baseline understanding of the biological basis upon which the midge control measures function. This is followed by 1.5 hours of midge control measures from the literature or the latest USDA research. After the farmers and ranchers have learned the basics, they have an opportunity to view the application of these control measures during a 1-2 hour tour of the host farm facilities. The NADeFA and ARS partnership is making a profound impact on the industry by creating new methods for preventing disease transmission on captive cervid farms and translating this information into actionable plans for their constituents and stakeholders through review articles, workshops, and presentations.
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Tchouassi, D.P., Okiro, R., Sang, R., Cohnstaedt, L.W., McVey, D.S., Torto, B. 2016. Mosquito host choices on livestock amplifiers of Rift Valley fever virus in Kenya. Parasites & Vectors. 9:184-191.
Huang, Y.S., Harbin, J.N., Hettenbach, S.M., Maki, E.C., Cohnstaedt, L.W., Barrett, A.D., Higgs, S., Vanlandingham, D.L. 2015. Susceptibility of a North American Culex quinquefasciatus to Japanese encephalitis virus. Vector-Borne and Zoonotic Diseases. 15(11):709-711.
Pfannenstiel, R.S. 2015. Extended survival of spiders (Aranaeae) feeding on whitefly (Homoptera: Aleyrodidae) honeydew. Journal of Entomological Science. 50(2):110-118.
Cohnstaedt, L.W., Fernandez-Salas, I., Clark, G.G. 2015. Mosquito vector biology and control in Latin America - A 25th Symposium. Journal of the American Mosquito Control Association. 31(3):286-296.
Kumar H.V., N., Nayduch, D. 2016. Dose-dependent fate of GFP-E. coli in the alimentary canal of adult house flies. Medical and Veterinary Entomology. 30(2):218-228. doi:10.1111/mve.12162.