MMore than 250 million people in about 30 countries are at risk of contracting a disease called river blindness, which can lead to permanent vision loss. But for now, the best way to monitor the disease is to use human volunteers as bait to collect the insects that carry the pathogen.
River blindness, or onchocerciasis, is caused by a parasitic worm. Onchocerca vortex— When midges infected with worms bite people, they transmit the worm larvae. The name “river blindness” comes from the fact that midges breed in fast-flowing rivers. Adult worms which can grow up to nearly 20 inches long, live inside a human host for up to 15 years and give birth to millions of baby worms called microfilariae. They can get on a person's skin and eyes, causing painful itching and chronic inflammation. In some cases, microfilariae cause eye lesions that can cause permanent blindness. River blindness is most common on the African continent, Yemen and parts of Latin America.
Although there is no cure or vaccine to prevent river blindness, the drug ivermectin kills microfilariae and can curb the spread of the disease when it is widespread in large populations. To monitor flies infected O. collarResearchers across Africa collect thousands of these insects every year. They do this by asking human volunteers to sit by rivers for hours, enticing midges to land on their skin, and catching flies with a glass tube—the only midge collection method currently recommended by the World Health Organization for such research.
Although volunteers are treated for river blindness beforehand as a precaution, the bites can still be painful. Prolonged exposure to such an environment may increase the risk of snake bites or exposure to other pathogens such as tsetse flies and mosquitoes. That's why Sightsavers, an international charity dedicated to preventing preventable blindness, wanted to develop an alternative monitoring method to track the midges that carry onchocerciasis.
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“Using people as bait, even if they have volunteered, raises big ethical questions,” said Louise Hamill, Sightsavers director of onchocerciasis, in her article. statement. “We clearly need a better solution.”
In collaboration with the Global Disease Eradication Institute and the ministries of health in Ghana, Côte d'Ivoire, Malawi and Mozambique, Sightsavers tested a variety of insect traps to catch midges. They assessed the effectiveness of 16 different versions of insect traps, known as Esperanza window traps, in midge breeding grounds in Ivory Coast, Malawi, Ghana and Mozambique, which were used from 2021 to 2025.
These traps contained carbon dioxide to simulate human respiration – both synthetic and CO2.2 derived from yeast, as well as different colors, sizes, shapes and smells. The team placed worn socks in some traps because the smell of human sweat attracts midges. They added artificial foot stink to other traps.
Ultimately, the ideal setup varied depending on location. For example, in Ivory Coast and Mozambique, where fly numbers were relatively low, yeast-derived carbon dioxide traps and worn socks were most effective. But in fly-infested Malawi and Ghana, both carbon dioxide sources and real and fake sock scents worked equally well.
Overall, the researchers found that seven pairs of these traps could perform as well as a single flytrap. “Traps are easy to set up and require minimal maintenance in the field,” Sightsavers noted in the report. A spokesperson for the organization said by email that the final results won't be released until next year, but the study culminated in the creation of a standardized data collection guide for local officials to monitor the spread of river blindness.
The project also resulted in a tool for predicting midge breeding sites using satellite data and machine learning to reduce the time people spend hunting for midges near rivers and putting themselves at risk of disease. The model achieved an accuracy of 83.1 percent, “indicating excellent predictive performance,” suggesting it could target surveillance to specific areas.
The researchers also noted that the traps could catch other insects that act as vectors for human diseases, which could help communities control multiple pathogens at once.
In addition, traps can help reduce midge populations by catching females before they can lay eggs. “This has the potential to offer communities long-term protection from river blindness,” the statement said.
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