Children infected with malaria can become “superspreaders” and pass the parasite to droves of local mosquitoes, even if the kids never develop symptoms of the disease, a new study suggests.
Since this disease is passed from humans to mosquitoes and then back again, rather than from person to person, this finding is worrisome.
If malaria goes untreated in these asymptomatic children, the parasites will continue to circulate among mosquitoes, even in places that employ intensive malaria controls like insecticides, bednets, and free diagnostic tests and treatments. According to new research, presented Wednesday (Nov. 18) at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH), even a small number of infected children can transmit malaria parasites to a mob of mosquitoes, which can then go on to infect more humans.
From their new research in Uganda, the researchers concluded that asymptomatic children between ages 5 and 15 are the main source of infection for local mosquitoes in the region they studied. Some of these children were so-called superspreaders, meaning they infected a much larger number of mosquitoes than others; in experiments where mosquitoes were fed blood samples from infected people, more than 60% of the resulting mosquito infections could be traced back to just four asymptomatic children, two of whom were school-age. The other two superspreaders were ages 3 and 4.
Despite some children becoming infected with multiple malaria clones during the study, these kids never fell ill and continued to lead a “normal life … somehow living with all these parasites,” said lead author Chiara Andolina, a graduate student and malaria expert at Radboud University Medical Center in the Netherlands. Malaria is well controlled in the region the team studied, but should control efforts ever falter or cease, these children could potentially fuel a resurgence of disease in the area.
To prevent malaria cases from rebounding, control efforts could specifically target school-age children, senior author Teun Bousema, a malaria epidemiologist at Radboud, told Live Science. For example, regular malaria screenings and treatment campaigns in schools could have a “very meaningful impact” on depleting reservoirs of malaria, and ultimately, driving the case count down to zero, he said.
Asymptomatic malaria infections make up 80% or more of the cases detected through comprehensive screenings in areas where the disease regularly circulates, Bousema said. Studies suggest that these asymptomatic infections crop up most often in school-age children.
While scientists agree that mosquitoes pick up malaria from both symptomatic and asymptomatic people, there’s a question as to whether one kind of infection is more or less infectious than the other. In search of the answer, the study authors traveled to the Tororo district of Uganda.
Malaria was once incredibly common in Tororo; as recently as 2011, each resident was bitten about 310 times per year by malaria-infected mosquitoes, Andolina said in her ASTMH presentation. Now, after years of intensive malaria control, infection rates have plummeted. In 2018, exposure to infectious mosquitoes fell to only 0.43 bites per person, per year.
“It’s sort of a blueprint for what you can expect — if you really invest very heavily in malaria control, you can bring malaria burden down,” Bousema said. But to completely eliminate malaria, scientists have to find and purge any remaining hideouts of the parasite, he added.
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