Research continues to combat mosquitoes and ticks

Understanding insect vectors, like mosquitoes, and the pathogens they can spread remains a top priority for public health agencies, and the Western Gulf Center of Excellence for Vector-Borne Diseases is leading those efforts.

Applied research has played an important role in the Western Gulf Center of Excellence for Vector-Borne Diseases as the institution spearheads efforts to combat mosquitoes, ticks and other vectors of human and zoonotic diseases.

After five years of research, Phillip Kaufman, Ph.D., head of the Texas A&M Department of Entomology, said projects have built a foundation for the center and its public health mission. Research by Texas A&M AgriLife Research and Department of Entomology scientists has been critical to the efforts to develop insect and disease control methods and forecasting tools for Texas communities.

“The center has made tremendous strides within its research, outreach and education mission, but research is a foundational element to long-term success when it comes to vector control and disease prevention,” Kaufman said. “Science focused on understanding vectors and providing novel methods to protect public health is the tip of the spear for this entire effort.”

Building research partnership

Disease outbreaks from viruses like dengue, chikungunya, West Nile and Zika in areas of the U.S. led to the creation of five regional Centers for Excellence in Vector-Borne Diseases.

The Western Gulf Center of Excellence for Vector-Borne Diseases is based at the University of Texas Medical Branch and includes partnerships with AgriLife Research and the Texas A&M AgriLife Extension Service along with other universities and public health agencies.  The Center has four counterparts that represent a $50 million, five-year grant program funded by the Center for Disease Control and Prevention, CDC, designed to bolster research, education and outreach efforts aimed at preventing vector-borne diseases.

Kaufman said the College of Agricultural and Life Sciences, the Department of Entomology and AgriLife Research have all played important roles in the university’s collective efforts for scientific progress against vectors and vector-borne diseases.

“The cooperative and complementary efforts by our scientists for the Western Gulf Center is indicative of the overall mission to improve our understanding of vectors like mosquitoes and how we can control them more effectively,” he said. “The past five years have created a strong foundation for future strides in this field that ultimately supports more robust research, education and outreach in support of regional public health.”

Evaluating mosquito control

Over the past five years, scientists have conducted applied research projects designed to examine mosquito resistance to insecticides and to evaluate vector intervention programs around the state, among others.

Gabriel Hamer, Ph.D., AgriLife Research entomologist, Bryan-College Station, said much of the research performed by Texas A&M scientists aimed to improve integrated mosquito management in the region. Creation of the center has helped focus research efforts on locally relevant challenges that offer potential for translation into improved public health practices.

Hamer’s work has been instrumental in the assessment of mosquito surveillance and control practices in cities and counties scattered across Texas. The collaboration of a local mosquito control program with an academic lab allows for access to additional tools or capacity that are often not possible in isolation. 

He and his team of students and staff worked with the City of Brownsville, Harris County Public Health and other agencies in the state to address this need.

“Evaluating how vector-control tools work is often the most neglected aspect of integrated mosquito management,” he said.

Building a community of practice

Through the Centers of Excellence, the CDC encourages “communities of practice,” defined as a group of people who share a concern, a set of problems, or a passion about a topic, and who deepen their knowledge and expertise by interacting on an ongoing basis.

Supporting the concept through research was a priority because communities of practice provide a collaborative framework for public health professionals to work with partners in academia and elsewhere to identify and leverage best practices and standards related to vector-borne diseases.

“The communities of practice aspect is one of the most exciting parts of our Center of Excellence,” Hamer said. “I think everyone is proud of how the center has spurred communication and collaboration.”

The many participants of the Center of Excellence scattered at multiple universities are publishing research results with university, local and state health agency personnel as co-authors. These products are testament to the effective networks that have been developed to reduce the perpetual challenges of siloed research activities not in touch with local needs, Hamer said.

One of Hamer’s research projects involving many local and state partners was a survey of Texas residents in Harris, Tarrant and Hidalgo counties regarding their acceptance and willingness to pay for mosquito control.

Many city and county vector control agencies are severely underfunded and lack resources for effective integrated mosquito management, and the results of this survey suggest an unmet demand for mosquito control in Texas.

“We started this project given the observation that the region has very few area-wide vector control programs at the city or county level, funded by local taxes,” he said.

Currently, the average amount of tax funding for vector control in these three counties is 78 cents per person per year, but the survey discovered that participants were willing to pay $53.15 in annual fees. Participants were also asked which control methods, including adulticides, larvicides, lethal traps and mass releases of modified mosquitoes, they were willing to support.

The survey found that most participants were overall supportive for all control methods, with the highest support for lethal traps and lowest support for genetically modified mosquitoes. This study was recently published in the CDC’s journal Emerging Infectious Diseases.

Developing disease control, forecasting tools

Additional AgriLife Research entomologists have been conducting applied research to evaluate efficacy of current control practices or to develop new disease forecasting tools.

Patricia Pietrantonio, Ph.D., an AgriLife Research Fellow and professor in the Department of Entomology, worked with the Harris County Mosquito and Vector Control Division to investigate mosquito resistance to organophosphates and pyrethroids, the only two adulticide chemicals approved for control applications.

Research looked to determine the type of molecular-resistance mechanisms present and their frequency in known vector mosquito populations. Better understanding the susceptibility of wild populations of mosquitoes to control products will improve decision making to ensure efficacy is being achieved and to reduce the additional development of resistance.

The assays determined two mutations in the pyrethroid target, the sodium channel, are associated with resistance for Aedes aegypti populations in Harris County. The work was published in the journal PLOS Neglected Tropical Diseases.

Female Aedes and Culex species mosquitoes were collected in Harris County and exposed to different pesticides including malathion and permethrin to estimate the percentage of resistant mosquitoes. For Culex quinquefasciatus, the main mosquito that transmits West Nile virus in this region, the mutation conferring resistance to pyrethroids is widespread in Harris County. The published research is now guiding control measures in these regions.

The study has also identified genotypes within mosquito populations that produce metabolic resistance to traditional pesticides when expressed.

Kevin Myles, Ph.D., professor, and Zach Adelman, Ph.D., professor and AgriLife Research Fellow, both in the Department of Entomology, investigated how temperature and humidity levels are coupled with mosquito immune responses to pathogens to predict transmission risk.

This work was accomplished by partnering with the Harris County Mosquito and Vector Control Division to deploy microhabitat sensors, which then informed the environmental conditions of mosquitoes reared in College Station insectaries. Mosquitoes receiving different larval conditions, which influences their immune system, were then evaluated for their ability to transmit Zika virus.

Kaufman said this type of research could help forecast outbreaks based on environmental conditions.

“Understanding the environmental factors that could fuel an outbreak by different mosquito-borne viruses is important,” he said. “Using disease forecasting tools that adapt to different microhabitat conditions experienced by the mosquitoes which inform transmission risk could be a promising approach.”

Investment fuels innovation, protection

The first five-year round of funded research within the Western Gulf Center faced some obstacles due to the COVID-19 pandemic, including suspension of lab and fieldwork at times. But Hamer said the center continued to facilitate dialogue among academic and public health partners as they juggled attention on the pandemic concurrent with vector-borne diseases.

For example, the Texas Department of State Health Services, in concert with the Western Gulf Center, started the Texas Tick Working Group in 2019 with quarterly conference calls to discuss tick research and public health priorities. These well-attended video conference calls continued during the pandemic and have provided communities of practice that never existed before regarding the threat of ticks to public health in the region.   

Hamer hopes the next round of CDC funding for the Centers of Excellence around the U.S. will continue to build on the foundation gained in the last five years and sustain the capacity to address the threats of tomorrow.

“It is an excellent fit for a land-grant university to be a partner in the Center of Excellence in Vector-Borne Diseases so that locally relevant applied research receives funding to address regional societal needs,” he said. “Partnerships among academia, public health agencies, pest professionals, and industry are all needed to manage the changing threats posed by insect vectors that impact human and animal health.”