In Sub-Saharan Africa, people spend time outdoors performing social activities before they sleep, or in the early mornings after they wake up. This increases their risk of exposure to mosquito bites, according to the study, which adds that outdoor mosquito bites compromise the effectiveness of indoor malaria prevention methods including the use of bed nets.
Researchers fixed chairs and ribbon mats with transfluthrin, a fast-acting pyrethroid insecticide that can repel and kill mosquitoes. Results of the study conducted between September 2019 and February 2020 in rural south-eastern Tanzania show a reduction of the mosquito densities or populations per given area.
“We demonstrated that mosquito-free outdoor spaces can be created by using simple and locally sourced interventions.”
John Paliga, Ifakara Health Institute
“The study is the first attempt to create long-lasting mosquito-free zones which can significantly expand protection against malaria mosquitoes and several other mosquito species,” says Fredros Okumu, a co-author of the study and director of science at the Ifakara Health Institute in Tanzania.
Researchers targeted Anopheles funestus and Anopheles arabiensis, which are prevalent in areas of Tanzania where government-supplied bed nets are widely used.
In the study, the researchers surveyed 200 households where repellent-treated chairs were mounted outside, and fitted underneath with fabric mats. Each morning and evening researchers captured mosquitoes through the use of net traps, counted and analysed them.
“Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70–85 per cent while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 77–81 per cent reduction in the general peri-domestic area,” says the study published in the Malaria Journal this month (10 March).
“Almost all the field-collected An. arabiensis (99.4 per cent) and An. funestus (100 per cent) exposed under transfluthrin-treated chairs died,” the study adds.
John Paliga, the lead author of the study and a public health entomologist at the Ifakara Health Institute, calls for the development of new tools to complement the current efforts aimed at eliminating malaria.
“We demonstrated that mosquito-free outdoor spaces can be created by using simple and locally-sourced interventions. We believe that they will have a significant contribution in reduction of malaria in communities,” Paliga says. “If we could reach a point where people live in the environment free of mosquitoes, this means that there would be no malaria transmission at all, but the journey to reach there is still long.”
Gordian Kikompolisi, a tropical disease control expert and technical specialist at Abt Associates, Tanzania, tells SciDev.Net that malaria-transmitting mosquitoes are changing their biting behavior, such as the time they bite and the areas they tend to inhabit.
“Continued supply of bed nets and indoor spraying as major preventive tools alone cannot address such a problem in Tanzania and other malaria-endemic countries,” explains Kikompolisi. “If treating outdoor chairs with transfluthrin can protect people from bites, that’s an important step in malaria prevention. It augments the current efforts.”
Kikompolisi adds that he has been studying the behaviour of An. arabiensis mosquitoes in south-eastern Tanzania and found them to be abundant, with increased outdoor-biting capabilities.
“I believe the study has come with a solution to such malaria-transmitting vectors. Authorities in Tanzania should consider [the solution] in the coming days.”