However, mosquitoes are developing resistance to insecticides, particularly pyrethroids, a compound widely used in ITNs and IRS. Furthermore, existing vector control tools only have the capacity to target mosquitoes indoor.
This underscores the urgency to reinforce the malaria toolbox by exploring new vector control strategies.
Nightwatch: Collecting host-seeking mosquitoes while residents sleep in their homes
Within the study clusters, households are mapped out. Upon obtaining consent from the residents, fieldworkers collect adult mosquitoes from the interiors of the homes, all while residents rest comfortably beneath their insecticide-treated bednets. They set up battery-powered light traps (CDC light traps) that collect mosquitoes that are attracted to the protected sleeper.
Our work begins when the rest of the village goes to sleep, and we rest when they rise for their days. - Miguel Gerson, Kenya
These mosquitoes are collected to gather information on:
- species composition and vector densities
- malaria infection status
- population age structure through the parity rate
- size of the adults
Capturing mosquitoes resting on the walls
Early in the morning, between 5 and 7 am, the fieldworkers look for adult mosquitoes resting on the indoor walls of the homes.
The mosquitoes are caught using battery-powered aspirators. The objective is to gather essential data on the source of their blood meal, how long they take to lay eggs after a blood meal, and how long they survive.
The 'often-forgotten' outdoors
Existing vector control measures like ITNs and IRS have predominantly focused on targeting indoor mosquito populations. However, as the tides of time shift, malaria-transmitting mosquitoes are adapting and increasingly choosing to strike outdoors.
Thus, to leave no stone unturned, the entomology team also ventures outdoors to collect mosquitoes in livestock enclosures and pit shelters and bring them back to the insectary for further analysis.
The entomology team does not shy away from swamps, puddles, ponds, and other potential sites where the malaria culprits breed.
Throughout the course of the study, they scoop out aquatic mosquito larval stages, using dippers.
They rear the collected larvae to adults in the insectary and conduct tests to monitor for insecticide resistance and bio-efficacy.
They come in all shapes and sizes
Since the beginning of the project, the entomology team has collected over 138,000 mosquitoes.
Out of the roughly 530 species of Anopheles mosquitoes, only 30–40 are known to transmit malaria in nature. In Mozambique, the most commonly found species of malaria vectors were Anopheles funestus s.l and Anopheles gambiae s.l.
It is interesting to see the significant contrasts stemming from our experiences in two distinct settings. During the rainy season in Mozambique, we could get as high as 2000 mosquitoes per house every night. In Kenya, so far our highest is 110. Furthermore, Kenya boasts a rich species diversity of secondary vectors, when compared to Mozambique. - Caroline Kiuru, BOHEMIA project
In addition to helping answer BOHEMIA's research questions, the entomology team has collaborated with malaria control programs in the trial areas to generate data for insecticide resistance profiles. "With this data, the malaria control programs can understand the vectors in their area so that they can make informed decisions on what tool is best suited for their local vectors," explains Kiuru.
The arrival of an invasive species
On February 10, 2023, the Kenya Medical Research Institute (KEMRI), an implementation partner of the BOHEMIA project, published an evidence brief confirming the presence of Anopheles stephensi in the country.
This invasive species has gained notoriety for transmitting both Plasmodium falciparum and Plasmodium vivax malaria. Flourishing equally in urban and rural landscapes, it displays resistance to a range of insecticides. In a mere span of years, this invasive species has swiftly extended its reach to new frontiers across Africa, posing a grave risk to the progress achieved over the years.