Malaria-carrying mosquitoes do up to 30 per cent of their biting indoors during the day. The finding could inform measures to combat malaria, which tend to focus on the insects’ nighttime feedings.
Malaria is a serious and sometimes fatal disease spread by female Anopheles mosquitoes. As the insects feed on blood to nourish their eggs, a parasite travels through their saliva and into their victim. In 2020, there were an estimated 241 million cases of malaria and some 627,000 deaths Earlier estimates of mosquito biting patterns assumed the insects fed mostly at night. But until now, their daytime biting behavior hadn’t been studied closely. When Claire Sangbakembi at the Institute Pasteur de Bangui in the Central African Republic noticed that mosquitoes in the capital city appeared to be biting around the clock, she decided to investigate. In June 2016, Sangbakembi her colleagues and a team of volunteers began a year-long mosquito collection project. Every month, working in six-hour shifts, they spent 48 hours collecting mosquitoes in four different locations around the city. As soon as a mosquito landed on them – but before it started to feed – the collectors trapped the insect inside a glass vial. Volunteers were compensated for their effort and treated with anti-malaria medication in the event they contracted the pathogen. Over the course of the year-long study, the team collected nearly, 8000 malaria-carrying mosquitoes from eight different species. Carlo Constantino at the University of Montpellier in France developed a model that displayed the insects’ feeding times over a 48-hour period. The analysis revealed that most biting events occurred indoors and between dusk and dawn, but to the researchers’ surprise, between 20 and 30 per cent of mosquito bites happened indoors during the daytime.
“It was kind of a shock,” says Constantino. He hopes the work will spur other entomologists to take daytime samples. If we really want to understand the extent of the problem, we have to start measuring malaria transmission in the right way, which is covering the whole 24-hour period. The two most widely used strategies for preventing malaria – hanging insecticide-treated bed nets and spraying insecticides – are prioritized largely within homes.
Diego Ayala, also at the University of Montpellier, says that insecticides could also be applied to other buildings where people spend a lot of time indoors during the day, including schools, workplaces and shops. “If we want to eradicate malaria, we might have to include those places,” he says. Update on 6 October 2021: The world’s first malaria vaccine, known as RTSS, was today recommended by the World Health Organization for general use among children in sub-Saharan Africa and other regions with moderate or high rates of malaria. It was previously used only in large-scale trials.
“We longed for it to come,” Janet Mule, told me, recalling her reaction to hearing that scientists were developing a vaccine against malaria. Mule, a nurse I met while travelling in rural Kenya, has seen the devastation caused by this disease first-hand. Each year, it sickens more than 200 million people globally, killing at least 400,000. The vast majority of cases are in sub-Saharan Africa, with the biggest burden falling on younger people. Malaria causes many complications for children anemia, organ failure, jaundice, liver complication, says Mule That could soon change, however. While most of the world is focusing on new vaccines for the coronavirus, thousands of Kenyan children are finally receiving a longed-for malaria vaccine, 37 years after development of it started. Since 2019, Kenya, Ghana and Malawi have been taking part in a pilot program coordinated by the World Health Organization (WHO). If it is successful, the vaccine will be rolled out to infants across Africa. As this went to press, trial results of another vaccine developed by the University of Oxford suggested it was 77 per cent effective.
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