Spraying to save lives: In Kenya, teams fight malaria-carrying mosquitoes

Sitting on the shores of Lake Victoria in western Kenya, Migori County is lush and green — and harbors mosquitoes that create a serious health threat to the county’s population. Despite being entirely preventable, malaria is a leading cause of sickness and death here.

To reduce the mosquito population, the county has deployed spray operators — people who travel to homes in villages across the county and spray every room with a human-safe, long-lasting residual insecticide proven to kill mosquitoes.

For local spray operators, their day begins before the sun is up. One day in March, a group of them gathered for a heavy meal before suiting up in protective gear and mixing the chemicals for the insecticide. They set off in groups to different villages. Each six-person team has a target of 60 homes per day.


“Spray operators are here today. Remove items from your home. Spraying is safe and will protect you from malaria.”

Community mobilizers used a megaphone to tell community members about the benefits of having their home sprayed with insecticide. Community mobilization is an important component of the program—information from the mobilizers dispels common misunderstandings and myths about spraying and increases the likelihood that homeowners will be willing to have their house sprayed.

Homeowners must remove all of their belongings before spraying can take place. After two hours, they can move their belongings back into their home and can sleep in the house that night, protected from mosquitoes and malaria.

Every house is marked with the date it was sprayed and the unique number identifying the spray operator.

After spraying homes, the spray operators emptied their spray bottles and followed careful procedures to dispose of chemicals in an environmentally safe manner.

Spray team leaders entered data for the day using mobile phones. This data shows how many homes were sprayed and in which location, helping the team stay on track of their daily target.


After biting someone, a mosquito will typically rest on a wall until it has digested the blood. If the person it has bitten is carrying the malaria parasite, that mosquito will then pass on the parasite to the next person it bites.

By spraying the walls with insecticide, the mosquito will come into contact with the chemical while resting on the wall and won’t survive long enough to bite—and infect—another person. In this way, the spraying disrupts the transmission of malaria in addition to reducing the mosquito population.

In Migori County, a team of entomologists (scientists who specialize in insects—in this case, mosquitoes) sampled homes to determine whether or not the spraying was effective. They brought mosquitoes in small containers and used their breath to blow mosquitoes gently onto different spots on a wall in recently sprayed homes.

The entomologists timed how long it takes for the mosquitoes to die as they rested on a sprayed wall and what percentage of the mosquitoes died. They discovered that all them died within 24 hours of being introduced to the wall—meaning the spraying was working.

Over a three-week period in March, the program sprayed households in six sub-counties in Migori, protecting over 900,000 people from malaria. The local spray operators congratulated themselves on a job well done.