The Net Detectives Vectorworks trains teams to understand how long insecticide-treated bed nets last -- and how to keep malaria-carrying mosquitoes away longer

The most effective weapon against malaria is an insecticide-treated bed net. These nets are distributed across sub-Saharan Africa in mass public health campaigns to ensure that as many people as possible sleep under them and are protected from being bitten by mosquitoes carrying the deadly parasite.

Bed nets have surged in popularity. In countries where malaria is common, an estimated 80 percent of people with a net slept under one last night. While malaria rates have steeply declined over the past 15 years, 400,000 people still die from the disease each year, primarily children under the age of five.

As part of its VectorWorks program, funded by the President’s Malaria Initiative (PMI), the Johns Hopkins Center for Communication Programs (CCP) doesn’t just help distribute bed nets in massive campaigns every three or four years. In five countries, including Tanzania, VectorWorks also conducts research -- called "durability monitoring" -- on how people use the nets, how they care for them, and how long they last, informing global policymakers.

Treated nets are responsible for 68 percent of the reduction in malaria cases since 2000.

That research is done by teams visiting the same 10 houses per village each year where they ask questions about net use and to search by hand for holes large enough for a tiny mosquito to fly through. Nets with fewer holes provide better protection from mosquito bites. Here, Safia Saleh Ali fills in a tally sheet, which helps data collectors keep track of the number and size of holes they find in each net.

The inspections aren't only visual, as nets aren't just a physical barrier between mosquitoes and the human blood they feed on. The other key to a net's success is the insecticide with which it is treated. Mosquitoes that land on a treated net pick up a lethal dose of insecticide and die before they bite anyone else, halting malaria transmission. To make sure the insecticide is still doing its job, the teams will take some nets back to a lab and test their effectiveness using live mosquitoes. (Not to worry: The teams provide new nets to replace the ones they take away.)

Here, workers are trained on how to spot, judge, and record the size of holes in the bed nets.

Last month in Zanzibar, an island off Tanzania's coast, Vectorworks Project Director Hannah Koenker, PhD, MPH, was on hand to help with the project’s training of durability monitoring teams and to see them in action. In two regions of Zanzibar, the team is conducting an annual study of nets in 300 households that received them in the summer of 2016. The nets were distributed by the Zanzibar Malaria Elimination Program, part of the Ministry of Health.

VectorWorks is looking for clues on how to keep nets in the best possible shape. Researchers like Ali, above, ask villagers how often they wash their nets, how many young children they have in the home and whether they tie the nets up during the day to keep them out of the way of small hands or chickens or goats, anything that can cause damage. All of these factors can impact the useful lifespan of a bed net.

"We can extend the useful life of a net by a year just by encouraging people to take better care of them. It's better than a manufacturer can do by improving seams or fabric or just about anything else," VectorWorks' Koenker says.

Here, about 30 minutes outside the capital of Zanzibar, teams of four fan out to where villagers live in mud huts with thatched roofs. They unhook the bed nets inside, bringing them out into the sun for examination. Two people hold up the net in order to allow the third to carefully inspect each of its five sides. The fourth interviews the head of household or their spouse.

A laminated guide helps researchers categorize the size of each hole based on its diameter. The hole in this net, the team determines, was likely made by a rat that nibbled away the material, probably to use for its nest.

Sometimes, families will try to repair the nets. Some tie knots. Some use needle and thread. Some try patches. All with different levels of success. These nets must last for at least two more years before the next mass distribution campaign launches.

Once a tally sheet is complete, the data are entered into a tablet computer and the sheet is wiped clean to be used again.

The teams will return each year to inspect these same nets. Understanding how long these nets offer protection from mosquitoes will help aid agencies and policymakers make the best possible decisions to protect the people who sleep underneath.

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