US Policy Leaves Country Vulnerable to Arthropod-Borne Diseases

The American dog tick (Dermacentor variabilis), male shown here, is a vector for several human diseases, including Rocky Mountain spotted fever. This male was collected at a state park in South Carolina. A new article in the Journal of Medical Entomology highlights problems with current government policy for managing vector-borne disease and the insects and arthropods that carry them and offers several recommendations for improvement. (Photo by Kyndall Dye-Braumuller, ECB)

By Leslie Mertz, Ph.D.

Leslie Mertz, Ph.D.

Leslie Mertz, Ph.D.

United States government policy makes the country vulnerable to outbreaks of West Nile virus, Zika, and similar so-called vector-borne diseases spread by mosquitoes, ticks, and other arthropods, and is helping to make such disease-carrying bugs more resistant to the chemicals used to fight them, according to a new article in the Journal of Medical Entomology.

This is a big concern, because vector-borne diseases (VBDs) currently account for more than 17 percent of all the world’s infectious human diseases, says the paper’s senior author Melissa Nolan, Ph.D., assistant professor of epidemiology and biostatistics at the University of South Carolina’s Arnold School of Public Health, and a Science Policy Fellow at the Entomological Society of America.

The news is not all bad. The research article notes a “great policy mechanism” already in place, as well as additional steps that will put the nation on better footing to curb VBDs.

The Problems With Reactive VBD Policy

Current policies in the US generally put a strong emphasis on quelling an immediate threat but falter when it comes to the necessary follow-up, and this is a major problem, Nolan says. She used West Nile virus as an example: A mosquito-transmitted and potentially life-threatening pathogen, this virus made its US appearance New York in 1999 and had spread across most of the country by 2005. “We did a good job controlling West Nile initially, but we failed when it came to going into the second phase of an outbreak response, which is continued long-term risk mitigation and management,” she says, noting that the lack of follow-up has resulted in persistent outbreaks about every three years in various parts of the country. “At this point, it is estimated that about 3 percent of all Americans have had West Nile virus, so it is an ongoing problem that we’ve essentially forgotten about, but it’s still a big cause of morbidity and mortality.”

Inattention to long-term management of disease-spreading arthropods also contributes to their increased resistance to management methods, she says. It happens because control measures reduce populations but don’t eradicate them. For example, control crews may spray an insecticide that kills off nearly all of the disease-transmitting mosquitoes in a particularly troublesome area, but that leaves behind those mosquitoes with some genetic variation that allows them to survive. Subsequent use of the same insecticide continues to amplify the prevalence of resistant mosquitoes and therefore becomes increasingly ineffective.

“Insecticide resistance is a huge issue,” Nolan says. “We looked at the national, regional, and a statewide [control organizations]and consistently across the board saw that they basically just keep spraying with the same chemicals that they’ve always used—they don’t switch them up—and they’re not monitoring for insecticide resistance, so that’s a problem.”

In addition, the paper’s authors found that local and regional control organizations are often not affiliated with a health department, so information about outbreaks of potentially disease-spreading mosquitoes isn’t communicated to health departments, who would otherwise inform healthcare professionals. “Failure to tell clinicians to start looking for VBDs in our patient population then leads to underdiagnosis and preventable mortality,” she says.

Some Solutions for Proactive Policy to Fight VBDs

One thing the US has done right, Nolan says, is the creation of five Vector-Borne Disease Regional Centers of Excellence in 2017 to assist academic researchers who are developing new and improved methods for monitoring populations of disease-causing arthropods and state health departments that are directing the day-to-day monitoring work. “It’s a great policy mechanism that bridges the academic and public worlds,” she says, noting that a five-year grant originally funded the Centers of Excellence through 2021, and new money will continue the program through 2027. “We would love to see that funding be sustainable and the centers be an ongoing program.”

The paper notes other steps that would strengthen the country’s fight against VBDs. One is increasing diversity within the field of entomology. “Whenever you increase the diversity of a team, you come up with better solutions,” she says. “For instance, if I was a city planning manager and had limited resources to use for doing monitoring and spraying mosquitoes, I might be biased in picking the locations I thought would be hardest hit if I didn’t have input from a more representative group of people who actually came from different neighborhoods.”

All vector-control programs should also lead community-outreach efforts to inform and engage the public and to build trust in and support for survey and control efforts, Nolan says. With input from a more diverse entomological workforce, including in leadership positions, better-tailored messages would result. For example, materials describing potential breeding grounds for mosquitoes might focus on bird baths in neighborhoods blanketed with manicured yards but focus on standing water in debris in neighborhoods dotted with vacant lots.

Although not addressed in the paper, the US would also do well to reach out to governments in Africa, Asia, and Latin America, which often have poor surveillance programs in place, and are the source of many of the invasive disease-carrying arthropods that have invaded the country, Nolan says. “Once we get US infrastructure really well established, we need to do more to create sustainable infrastructure in these other nations. That would benefit our overall work here.”

Leslie Mertz, Ph.D., writes about science and runs an educational insect-identification website, www.knowyourinsects.org. She resides in northern Michigan.

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