Immune-inspired public health strategy improves detection of disease-carrying insects

A disease surveillance strategy modeled on the body’s immune system detected more disease-carrying insects than the typical, top-down approach used conventionally, according to a study led by researchers from the Perelman School of Medicine at the University of Pennsylvania and the Universidad Peruana Cayetano Heredia in Peru.  Their work was published recently in PLOS Neglected Tropical Diseases.

Conducted in the city of Arequipa, Peru, the work targeted Chagas disease, a deadly parasitic affliction that can cause heart failure among other problems, that is a significant public health threat. It’s caused by a parasite that is transmitted to humans by blood-sucking triatomine insects, also called “kissing bugs,” or, in Peru, “chirimachas.” Public health efforts to reduce Chagas disease have focused on eliminating chirimacha infestations by treating houses with insecticides. Once the houses are treated, they must be monitored to make sure the insects do not return—a difficult task in a city of one million residents.

“The old way to surveil cities for disease vectors has its roots in the military—personnel are treated as soldiers and sent to find the bugs—the enemy—following strict rules and quotas,” said primary author Michael Levy, PhD, a professor of Epidemiology. “We changed the analogy and thought of surveillance more organically, as an immune system, made up of independent actors—like immune cells—who communicate with one another in a system that is flexible to expand and contract in response to the size of the problem.”

In a randomized trial, the new approach uncovered 23 infested households, compared with only five detected through the conventional strategy.

“Since the current approaches are extremely top-down and rigid, we believe that we found a more effective way to tackle these problems by encouraging the initiative of households and local health workers,” said Levy.

A more flexible surveillance model

The conventional approach to chirimacha infestations features a central public health authority that directs personnel seeking to stop vectors (a term meaning living carriers of disease) to likely areas of infestation. These personnel must enter and inspect the households they are assigned, spraying insecticide wherever they find chirimachas.

People in households not already assigned to vector control efforts can request spraying of their homes, but only by capturing a chirimacha and bringing it to a local public health facility for identification. Detection of an infestation in one household is followed by inspection of immediately adjacent households.

Levy and his colleagues decided to put forth a decentralized and flexible system of pathogen detection and response. This system allowed local public health staff to accept reports of infestations by phone call, social media, text message, and WhatsApp messages through a well-publicized “AlertaChirimacha” system. Vector control inspectors then received neighborhood-level infestation risk estimates, but they could also use their own judgment when deciding where to inspect. When they found an infestation, staff from nearby areas helped expand outreach—similar to immune cells swarming to the site of an infection—by distributing flyers, placing posters in local shops, and targeting AlertaChirimacha Facebook posts to nearby residents for 10 days. The response than ‘down-regulated’ once the insects were eliminated.

The study ran from October 2021 to March 2023. Researchers divided chirimacha surveillance zones in Arequipa into 60 clusters of about 2,300 households each, randomly assigning 30 clusters to the conventional strategy and 30 to the immune-inspired strategy.

By the study’s end, the immune-inspired approach had uncovered 23 infested households: 10 through primary detections or reports and then 13 more when those original detections led to expanded coverage nearby. The conventional approach uncovered just one primary infestation and four additional infestations in surrounding households.

The findings suggest that more decentralized, immune-inspired surveillance strategies should be studied in other settings and at larger scales, Levy and colleagues said.

“We suspect that the real power of this strategy will be revealed if it is expanded to address multiple competing disease threats, though it remains unclear whether abandoning old militaristic systems for the more adaptable immune approach will be palatable to public health agencies,” Levy said.

Editor’s Note: This research was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under award number R01AI146129.