Mosquitoes can transmit the malaria-causing Plasmodium parasite to humans. The disease was estimated to affect about 228 million people in 2018 and caused around 405,000 deaths that year according to the World Health Organization. Malaria poses a threat to about half of the global population, but the burden falls mostly in sub-Saharan Africa, where 93 percent of cases and 94 percent of deaths from malaria occur. The malaria parasite has been able to develop resistance to anti-malarial drugs. The World Health Organization has launched several efforts aimed at reducing the numbers of these drug-resistant Plasmodium parasites, but pockets of resistant parasites emerged in various locations even while those efforts were underway.
Mosquito-control measures are still the primary way the disease is prevented. While one vaccine is available, it's only against the P. falciparum parasite, and in clinical trials, only prevented about four in ten cases. Malaria immunity is still not well understood. It can take many exposures for people to build resistance to the disease.
In new work that could help scientists create a better vaccine, scientists have learned more about how the Plasmodium parasite influences human genes, which changes how the human immune system responds to malaria infections. An international team of researchers assessed blood samples from children in Burkina Faso, West Africa, where the disease is endemic, to examine the immune system before, during, and after malaria occurs. They revealed a novel strategy Plasmodium uses to evade the immune system. The findings have been reported in Nature Communications.
The study showed that microRNAs, which help control the activity of immune genes, can cause the death of adaptive immune cells exposed to Plasmodium. After getting around the immune system in this way, the parasite can then proliferate and infect other cells in the blood. Because microRNAs are also dependent on genetic factors, this may help explain why the severity of malaria infections varies in different people.
"Our results shed new light on a mechanism for the weakening of adaptive immunity by invasive parasites," said study author Aïssatou Diawara. "This could explain why it takes years for children to develop immunity and why vaccines do not provide long-term protection," added study author and Associate Scientist Mame Massar Dieng.
"The next step for the team will be to perform more functional tests and to gain a better understanding of why certain groups of people in Africa are more immune to the disease than others," said study author and New York University - Abu Dhabi Assistant Professor of Biology Youssef Idaghdour. "Due to the impact of COVID-19 on healthcare systems, and screening and prevention programs, the burden of malaria could be worse in the coming years and it is our hope that this research can contribute to reaching the long-term goal of malaria elimination."