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Mitigating Impacts of Vector-Borne Diseases

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The ARS veterinary, medical, and urban entomology research program mitigates the health and economic impacts of arthropod vectors and the diseases that they transmit to livestock, humans, and other animals. ARS collaborates across the human, animal, and environmental health communities to achieve sustained health outcomes for both animals and people. Economic losses from arthropod damage exceed $100 billion annually. The following FY 2019 accomplishments illustrate ARS efforts to eliminate arthropod vectors and nullify their impacts. Hyperlinked accomplishment titles point to active parent research projects.

New tick-borne disease diagnostic assay. Most tick-borne diseases can be transmitted by infected ticks through their bite from animals to humans. Enhanced pathogen detection is needed to improve the diagnoses of these diseases. The TickPath Layerplex is an innovative molecular assay that detects several tick-borne pathogens from ticks, animals, or humans. It is being patented by ARS scientists in Kerrville, Texas, and collaborators at Texas A&M University–College Station. The TickPath Layerplex detects several groups of tick-borne pathogens in a sample, distinguishes the type of tick-borne pathogen, and thereby guides decisions for rapid and appropriate treatments. This biotechnology aids in the diagnosis of human and animal tick-borne diseases.

Easily deployed spatial repellent provides protection from disease vectors. Standard pesticide sprays can reduce mosquito and biting fly attacks. However, they also contribute to insecticide resistance, which undermines their long-term utility. ARS scientists in Gainesville, Florida, and collaborators determined that the spatial repellent transfluthrin applied to strips of camouflage netting and geotextiles used ubiquitously by the U.S. military can be easily transported and attached to perimeters and structures to create a rapid shelter from biting and disease-vectoring insects. Significant reductions of incursions by mosquitoes, sand flies, and other biting flies were documented in protected perimeters across four ecologically distinct and militarily relevant environments. Thus, deployment of vector protection occurred without having to wait for intervention by mosquito and vector control units. In addition, the spatial repellent protected the perimeters without causing death of the targeted pests. By not killing the insects, the development of insect resistance is impeded by allowing insecticide-susceptible insects to dilute populations of insecticide-resistant pests.

Salivary proteins of biting midges associated with virus transmission in livestock. Until this research occurred, the extreme efficiency with which biting flies (midges) can transmit some viruses was not clearly understood. ARS scientists in Manhattan, Kansas, discovered that when virus-infected midges bite seeking blood, they transmit the virus as well as 45 proteins in their saliva that are critical for successful acquisition of a bloodmeal. A mouse model showed these salivary proteins promoted rapid infection and systemic dissemination of midge-transmitted viruses via the lymph system. Additionally, saliva-induced blood vessel dilation encourages virus replication and dissemination via the circulatory system. This research advances our understanding of the complex myriad of proteins in midge saliva and provides insights into their functional role in blood feeding, virus transmission, and viral disease pathogenesis. This fundamental research guides the development of methods to impede virus transmission in livestock.

Improved diagnostic kit in commercial development for all quarantined fire ant species. The red imported fire ant and the black imported fire ant are invasive species that cost the United States more than $6 billion annually in damage and control measures. The Federal imported fire ant quarantine program requires commodities to be free of both species before leaving quarantine. ARS scientists in Gainesville, Florida, with Animal and Plant Health Inspection Service scientists in Biloxi, Mississippi, developed a simple-to-use and portable identification kit (analogous to a home pregnancy test) that can distinguish both fire ant species from all other ants in a single, 10-minute test. The speed of the test curtails extended delays at inspection stations by eliminating the need to send off samples for identification. Being able to distinguish the black imported fire ant is an important improvement over the previous kit (InvictDetect) the scientists developed, which detected only the red species. The improved kit provides a new tool for regulatory agencies in the United States and other countries to enforce quarantine protocols that limit the spread of one or both invasive ant species. The license for this new technology has been acquired by Agdia Inc. and is currently being developed for commercial distribution.

Surveillance of pesticide resistance in southern cattle fever tick (SCFT). The SCFT may be the most economically important tick species due to its negative impacts on beef and milk production. Keeping the United States free from SCFT depends on the quarantine of infested premises and the systematic treatment of cattle with pesticides to suppress tick populations. The development of pesticide-resistant SCFT populations is becoming a problem and is associated with the intense use of pesticides to keep livestock free from SCFT. A rapid molecular test was developed by ARS scientists in Kerrville, Texas, to simultaneously detect different mutations in the SCFT genome associated with resistance to pyrethroids, a pesticide commonly used against ticks. Results from the test were used to evaluate the temporal epidemiology of pyrethroid resistance and SCFT outbreaks in the United States. Rapid surveillance for pesticide resistance is critical in the design of strategies to prevent the development of pesticide-resistant SCFT populations and to promote sustainable SCFT management.

Development and validation of CRISPR-Cas9 for gene knockout in screwworms. The continual release of sterile screwworms is essential to the successful eradication of this insidious and economically important pest of livestock and wildlife in Central and South America. ARS scientists in Kerrville, Texas, collaborated with scientists at the University of North Carolina and University of Campinas in Brazil to develop and validate methods for using the genome editing technology CRISPR-Cas9 in the screwworm. CRISPR-Cas9 can be used to selectively knock out a target gene and insert transgenes in specific locations in the genome. This technology is a key tool in developing gene drive strains and can be used to understand gene function. The technique was verified by knocking out genes for body color, olfaction, and sex determination. This method can be used to advance the sterile screwworm release program with gene drives or female-to-male transformation systems.