School-age children with no malaria symptoms could serve as super-spreaders of the disease, an observation that could open a new chapter on malaria control, a meeting has heard. The new findings from a study that was conducted in Uganda were reported at the virtual annual meeting of the American Society of Tropical Medicine and Hygiene last month (18 November).
"It is of great importance to understand who transmits malaria. This is particularly important in areas where malaria control is successful," says Teun Bousema, a co-author of the study and professor of epidemiology of tropical infectious diseases specialized in the biology and epidemiology of Plasmodium falciparum at Radboud University Medical Center in the Netherlands.
Bousema tells SciDev.Net that those running control programmes need to know whether malaria may come back and who in the human community can cause mosquito infections to help in determining when disease control can become less rigorous or when resurgence is very unlikely.
"In some ways, our study is a blueprint of what can be expected in other countries where mosquito control is very successful. Malaria will not disappear completely. It will persist in some populations," adds Chiara Andolina, a co-author of the study and a doctoral student at the Radboud University Medical Center, who presented the findings at the meeting. "We now have the first direct evidence that even in places under very intensive malaria control, a small number of asymptomatic super spreaders can quietly sustain transmission — and finding and treating them could prove very challenging."
Researchers assessed the transmission of malaria among children showing symptoms of malaria and those who did not present symptoms in Tororo district, eastern Uganda. The area has been targeted with malaria control measures, including regular distribution of insecticide-treated bed nets, indoor residual spraying with insecticides and access to effective malaria drugs.
Researchers conducted regular tests for evidence of malaria parasites on 531 people, including children aged five to 15 years old over a 24-month period.
According to the findings presented at the meeting, a school-age child who showed no symptoms despite harboring seven different variations of the malaria parasite Plasmodium falciparum "was responsible for 24.7 per cent of all infected mosquitoes infections observed".
"In this unique longitudinal study, we find that asymptomatic infections [with no symptoms] in school-age children are responsible for the majority of onward transmission events," the study adds.
They are very prone to infection and keep their infections longer because they have some level of immunity that prevents symptoms but not infection. Malaria-free school initiatives can have an important impact. Not only for school children but, as we show, also for the wider community since they are important transmitters of the infection."
Teun Bousema, Co-author, Professor of epidemiology of tropical infectious diseases, Radboud University Medical Center, Netherlands
Andolina tells SciDev.Net that such children can be easily targeted with interventions such as medicines that can prevent them from acquiring parasites at all as they are easily accessible in their schools. Lauren Cohee, a pediatric infectious disease specialist at the University of Maryland School of Medicine in the United States, says that the findings offer insights into malaria control.
"The extent to which transmission may be driven by a small number of highly infectious individuals is surprising and may open a new chapter for malaria control," adds Cohee. But Cohee explains that the yardstick used to measure malaria control interventions has traditionally been how many lives are saved or how many deaths are averted. "While this is clearly an essential metric, policymakers should consider the impact of control interventions on transmission," Cohee adds.