Diversity of Plasmodium falciparum across Sub-Saharan Africa
Scientists from the Walter Reed Army Institute of Research joined a network of African scientists, the Plasmodium Diversity Network Africa, and Wellcome Trust Sanger Institute to publish a groundbreaking study about the genetic diversity of the world’s most dangerous and prevalent species of malaria, Plasmodium falciparum across sub-Saharan Africa.
Malaria, infecting approximately 219 million individuals in 2017, remains a meaningful threat to public health and regional stability. One of the top five infectious disease threats to deployed Service Members, it is also a cause for concern for the U.S. military, whose investments in malaria research have supported the development of most FDA-approved malaria prevention and treatment drugs, as well as the world’s most advanced malaria vaccine, RTS,S. Though infection rates have been decreasing, this decline has stagnated in recent years, necessitating novel interventions.
This study, published in Science, utilized whole genome data from 2263 P. falciparum isolates from 24 sites in 15 countries to provide novel insights into the depth of genetic diversity and distinct regional character of the parasite across the continent of Africa.
Human and natural history are the most likely explanations for the identified genetic variation. Human movement across the continent, driven at first by migration across the continent then subsequently colonization and slavery — or lack thereof in the case of Ethiopia which was not colonized — may explain the highly-differentiated parasite population from the rest of Africa. By contrast, parasites from distant former French colonies share genetic material.
The introduction of malaria drugs has also had a major impact on the divergence of the parasite. New signatures found in P. falciparum in Malawi and Ghana may be due to the selection pressure introduced by artemisinin-based combination therapies, first-line treatment for uncomplicated malaria in most of Africa. Geneflow between subpopulations could spread drug resistance from one subpopulation to the rest of the continent.
“Malaria is one of the most important parasitic diseases with one of the largest genomes dedicated to immune escape, a shape shifter that morphs into more than 12 different shapes and stages in two hostile environments in the human host and the vector,” said Lt. Col. Edwin Kamau, an author on the paper and scientist at WRAIR, underscoring the difficulty of malaria control and elimination.
As malaria drug resistance develops and spreads between the distinct P. falciparum populations facilitated by human movement in all directions across Africa, understanding the regional characteristics of the parasites becomes increasingly critical to ensuring targeted, effective interventions. “The race is on to identify and validate drug resistance markers for ACTs and other interventions in Africa and other malaria endemic parts of the world,” said Dr. Ben Andagalu another author on the paper who is at the U.S. Army Medical Research Directorate-Africa, a subordinate directorate of the WRAIR headquartered in Kenya.
WRAIR and its partners remain committed to developing novel interventions to prevent the transmission of malaria, including mosquito repellents, chemoprophylaxis, biologics and more in order to eliminate the threat towards Service Members.
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