Location: Arthropod-borne Animal Diseases Research2010 Annual Report
1a. Objectives (from AD-416)
Objective 1: Assess the risk of endemic arthropod vectors to transmit introduced exotic arboviruses in North America. • Sub-objective 1.A. Determine the vector competence of the primary U.S. bluetongue virus (BTV) vector, Culicoides sonorensis, for EU-BTV-8. • Sub-objective 1.B. Create models to assess potential population densities for biting insects that might be involved if Rift Valley fever virus was introduced to North America using ecologic and climatic factors. Objective 2: Identify targets and evaluate tools for vector control and interruption of transmission cycles to protect livestock and humans from vector-borne pathogens. • Sub-objective 2.A. Identify molecular components in insects that can be targeted to interrupt orbivirus transmission cycles. • Sub-objective 2.B. Evaluate insecticide resistance of Culicoides sonorensis to common pesticides used in livestock and agricultural operations. • Sub-objective 2.C. Provide livestock entomologists improved identification tools for North American Culex tarsalis and Aedes vexans.
1b. Approach (from AD-416)
Livestock are often heavily exposed to biting arthropods, causing a number of animal health issues and making them vulnerable to infection with a wide range of insect-borne pathogens. This research program will focus on: 1) improving risk assessments of the potential for introduction of foreign disease agents into the U.S., 2) interrupting transmission cycles at the vector level, 3) identifying viable pesticides for control of vectors, and 4) improving vector identification and understanding of population dynamics to enable more efficient vector control. Determining the vector competence of Culicoides sonorensis for an exotic bluetongue virus (BTV-8) will give an indication of the potential risk for the spread of exotic BTV should it be introduced into North America. Targets for controlling C. sonorensis infection with orbiviruses will come through identification of insect cell receptor(s) for BTV and verification of specific genes associated with orbivirus infection in the insect using RNA interference. Determining the susceptibility of C. sonorensis to common insecticides will identify effective treatments for control of this important livestock pest. Development of predictive models to determine risk of arbovirus transmission, such as Rift Valley fever virus, based on predicted mosquito population densities and distributions will give weeks or months advance notice, allowing preventive measures to reduce or prevent animal and human disease. Understanding the population structures of Aedes vexans and Culex tarsalis through molecular data will provide useful information for field entomologists and agencies developing control strategies and for use in developing models to predict risk of arbovirus transmission.
3. Progress Report
Virulent bluetongue virus (BTV) from the European outbreak (EU-BTV-8) was received, propagated, and is ready for use in vector competence studies for the primary North American vector of BTV, Culicoides sonorensis. The first year surveillance data for Culex tarsalis and Aedes vexans populations was collected. Ecological and climate data that correspond to the mosquito population data has been compiled, and is being analyzed for linkages with the mosquito population data. The CDC’s bottle bioassay was adapted for use with Culicoides sonorensis using the three laboratory colonies available at the ABADRU. Modifications were made with regards to how insects are introduced into the bottle bioassay, the length of time between each observation, and the dosages of insecticide that are required to kill susceptible insects. Optimal bottle dosages have been calibrated for five different insecticides (Malathion, Fenthion, Sumethrin, Resmethrin, Permethrin). The assay is ready to use on field-collected specimen for these insecticides to test for insecticide resistance. Work on a degree day model for predicting whether/when Rift Valley fever virus (RVFV) could be transmitted should it be introduced into the United States has continued. The model is being refined using data on the effect of temperature on infection in the insect and improved climate data.