Location: Arthropod-borne Animal Diseases Research
2018 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
Objective 1. (1a) Changes in the microbiome of dairy cattle manure across house fly development from egg to pupae was assessed and revealed significant alteration of both prokaryotic (bacterial) and eukaryotic (protists, fungi) microbes. Since these microbiota serve as nutrition for the larvae, the next steps are to investigate how different larval substrates (such as other types of animal dung) affect larval development and also how they change over time due to larval grazing.
(1b) Interactions between bacteria and the house fly gut ultimately determine microbe fate and transmission potential. Recent studies have been aimed at understanding aspects of bacteria (species, abundance) and flies (immune response in the gut, sex of fly) and how these ultimately impact vector competence for pathogens. Bacteria species, the ingested dose (number) and fly sex all affect microbe persistence, proliferation and excretion. The interaction of these factors is a current focus of ongoing experiments.
Objective 2. Mathematical, epidemiological, and network modeling were used to predict the hypothetical spread of Japanese encephalitis virus (JEV). These models included environmental (weather and climate), biological (animal hosts and reservoirs), and insect vectors (mosquito species abundance and distribution). The models suggest that JEV is introduced to the United States from Asia every year but to date it has failed to establish and persist in the United States. This is mainly due to a lack of pigs/feral swine near ports of entry (sea or air ports). However the mosquito vector species which have important characteristics (feed on birds and mammals, vector competent, and are abundant) and bird reservoirs (long distance migration, low but persistent viremia, and high abundance) are present, therefore there is a risk of introduction and establishment of this deadly mosquito transmitted virus.
Objective 3. Culicoides salivary protein D7 has been has been cloned and expressed. D7 has been determined to be a potent allergen involved in eliciting mast cell degranulation during midge feeding. This leads to vasodilation and hemorrhage which facilitates midges to feed to repletion. The midge salivary protein late trypsin has been cloned and expressed, and purification is being optimized.
Bottle bioassays have been done to assess the efficacy (mortality) of various pyrethroids on colony biting midges. Biting midges are incredibly susceptible to pyrethroids and are “knocked down” and rendered immobile miniscule amounts of active ingredient within five minutes of exposure. However given 24 hours to recover, almost all biting midges will recover post exposure.
Accomplishments
1. Epidemiological modeling. ARS scientists in Manhattan, Kansas in collaboration with Kansas State University researchers quantified the current risk of Japanese encephalitis virus to the U.S. The introduction risk is currently minimal from planes and cargo ships based on a quantitative and qualitative pathways risk assessment analysis given the current trade and transportation routes and environmental conditions; a meta-analysis of the vectors and vertebrate hosts; and a meta-analysis of the insect vector infection, dissemination, and transmission rates. This is all summarized in a systematic review of the literature. Furthermore, based on these five publications, a sixth is in review regarding the placement of the vector in the epi-triad (pathogen, environment, and host) because the insect vectors responsible for vector-borne disease transmission play a more significant role than currently portrayed. The new representation better explains how disease vectored pathogens rely on the vector and this opens more control options, which is more accurate to the current outbreak control strategies. Together these studies demonstrate to epidemiologists, state and federal mosquito management districts, and health care specialists the need for continued surveillance and population management of disease vectors to prevent outbreaks of pathogens in humans and livestock.
2. Network modeling. ARS scientists in Manhattan, Kansas in collaboration with Kansas State University researchers determined the hypothetical spread and impact of Japanese encephalitis virus (JE) and Rift Valley fever virus (RVF) after an introduction to the U.S. In the event of an outbreak of JE or RVF in the U.S., understanding the roles of the hosts and vectors in geographic spread will be essential. To this end, network modeling was used to model the spread of viruses between farms and states in the Midwest, Texas, and the eastern seaboard. The model was developed using data from outbreaks in South Africa and then applied to farms in the United States. The data was based on mosquito species (vector capacity), weather (temperature and humidity), and host species. Geographic locations and trade between farms was also considered. In the case of JE, migratory birds were also considered as reservoirs for long-distance migration. This information is important for states and federal emergency planners who may need to rapidly react to introductions of exotic pathogens to protect the food supply.
3. Mathematical modeling. ARS scientists in Manhattan, Kansas in collaboration with Kansas State University researchers used case data analysis for retrospective analysis of disease vectors. Human case data is valuable and with mathematical and geographical modeling it can be used to understand the past parameters which allow for outbreaks or geographic expansion of the outbreaks. To examine geographic trends, past cases of Lyme disease were used to track the spread of Lyme disease in Connecticut. The analysis found two introductions into Connecticut and quantified a linear rate of spread as the pathogen introduction to new areas resulted in peak numbers of yearly cases which declined after establishment to stable yearly transmission. For Japanese Encephalitis, historical case data, a particle filter was used to estimate past vectorial capacity parameters when combined with temperature and precipitation. This was useful because it allowed for predictions of future cases based environmental parameters.
4. Genome of the biting midge (Culicoides sonorensis). Female Culicoides sonorensis biting midges harbor and transmit viral pathogens that cause sickness and death to ruminant livestock and deer. ARS scientists in Manhattan, Kansas, worked with a diverse group of national and international researchers to sequence and annotate the genome of this important vector. New genetic resources such as this genome will significantly advance research capabilities by providing access to genetic targets for novel pesticides, repellants. Further, identification of genes involved in key defense processes can help elucidate the molecular basis of vector competence, i.e. the midge’s ability to transmit pathogens.
Review Publications
Nayduch, D., Zurek, K., Thomson, J., Yeater, K.M. 2018. Effects of bacterial dose and fly sex on persistence and excretion of Salmonella enterica serovar Typhimurium from adult house flies (Diptera: Muscidae). Journal of Medical Entomology. 55:1264-1270. https://doi.org/10.1093/jme/tjy055.
Mills, M.K., Ruder, M.G., Nayduch, D., Michel, K., Drolet, B.S. 2017. Dynamics of epizootic hemorrhagic disease virus serotype 2 infection within the vector, Culicoides sonorensis (Diptera: Ceratopogonidae). PLoS One. https://doi.org/10.1371/journal.pone.0188865.
Cohnstaedt, L.W., Disberger, J.C., Paulsen, E., Duehl, A. 2018. Key elements of photo attraction bioassays for insect studies or field monitoring programs. Journal of Visualized Experiments. 1:1.
Oliveira, A., Cohnstaedt, L.W., Cernicciaro, N. 2018. Japanese encephalitis virus review: Placing disease vectors in the epidemiologic triad. Annals of the Entomological Society of America. https://doi.org/10.1093/aesa/say025.
Oliverira, A., Etcheverry Hernandez, L., Strathe, E., McVey, D.S., Piaggio, J., Cohnstaedt, L.W., Cernicchiaro, N. 2018. Quantification of vector and host competence for Japanese encephalitis virus: a systematic review of the literature. Preventive Veterinary Medicine. https://doi.org/10.1016/j.prevetmed.2018.03.018.
Cohnstaedt, L.W., Schmelz, E., Poland, J. 2016. Review articles and the depreciation of scientific currency. Science. https://doi.org/10.1093/aesa/saw061.
Cohnstaedt, L.W., Snyder, D. 2016. Insecticidal sugar trap for biting midges. Veterinaria Italiana. https://doi.org/10.12834/VetIt.572.2734.2.
Cohnstaedt, L.W., Snyder, D., Maki, E.C., Schafer, S. 2016. Crowdsourcing methodology: establishing the Cervid Disease Network and the North American Mosquito Project. Veterinaria Italiana. 52:195-200.
