115 years of malaria data collected in Africa, described today in Nature, gives the most detailed picture yet of where efforts to control malaria infection are being won and lost across the continent.
The largest data repository of any parasitic disease in the world, it includes 7.8 million blood samples from more than 30,000 locations in 43 countries. The dataset was collected and analysed by KEMRI-Wellcome Trust researchers based in Kenya, and is the result of over 20 years of research funded by Wellcome.
The study shows that sub-Saharan Africa has experienced a decline in the prevalence of P. falciparum – a parasite that causes malaria - from 40% prevalence in children aged 2-10 years old between 1900 and 1929 to 24% prevalence in the same age group between 2010 and 2015. This trend has been interrupted by periods of rapidly increasing and decreasing transmission, thought to be the result of several contributing factors.
The study reveals that although previous global initiatives have contributed to an unprecedented decline in infection since 2000, reductions have not occurred uniformly throughout the continent, leaving large parts of West and Central Africa with high transmission rates of the disease.
The researchers argue that new tools are needed for the low income and high malaria burden areas of Africa, where gains in malaria reduction have stalled. The researchers identify several challenges to malaria control, including emerging insecticide and drug resistance, and inadequate funding plans for replacing long-lasting insecticide-treated nets.
Professor Bob Snow, Principal Investigator at the KEMRI Wellcome Trust Research Programme and the University of Oxford, said “The history of malaria risk in Africa is complex; there have been perfect lulls when drugs worked and droughts prevented mosquitos transmitting the infection, and there have been perfect storms when drugs stopped working and flooding affected large parts of Africa.”
“While there has been substantial progress in malaria reduction in Africa, on average 1 in 4 children still carry the malaria parasite in Africa and there are areas of the continent that haven’t changed much over the last 3 decades. Focusing just on elimination at the margins of Southern Africa, runs the risk that high burden countries in Africa get ignored and left behind. If insecticide and drug resistance becomes established, or excessive rainfall hits Africa again, malaria will revert in large parts of Africa to the high levels we saw in the 1990s. This is a real wakeup call, we need new drugs and insecticides or the gains we’ve seen will be lost.”
Mary De Silva, Head of Population Health at Wellcome, said: “Malaria can be fatal if it isn’t diagnosed and treated promptly. The African region carries disproportionately high levels of infection risk; with over 90% of malaria cases and 92% of malaria deaths according to the 2016 WHO World Malaria Report.”
“This incredibly comprehensive study, the result of 21 years of research and hundreds of peoples’ contributions, is importantly now openly available for others to use. Working together, scientists can use these data to help us make sense of the changing nature of malaria in Africa and inform future responses”.
A history of malaria in Africa since 1900
One of the biggest historical drops in malaria followed the Second World War with the discovery of DDT and chloroquine.
Malaria prevalence was low during the late 1960s, through the 1970s and early 1980s. This was a period when, despite low investment in malaria control in Africa, chloroquine use was widespread with repeated dosing available to the general population. Together with drought across the Sahel, this produced a lull in malaria transmission.
Chloroquine resistance expanded across Africa in the 1980s, and in the late 1990s unprecedented rainfall led to flooding and major malaria epidemics. Ministries of Health across the continent woke up to the perfect storm without any significant mosquito vector control in place. Malaria prevalence returned to the levels seen before the Second World War.
The financial response by the Global Fund and the technical revisions to policy by the World Health Organization after 2005 led to one of the largest drops in malaria infection prevalence witnessed since 1900. This saw the rolling out of insecticide treated bed nets and new drugs to treat malaria.
Between 2010 and 2015 the decline in malaria prevalence has stalled.
The research was led by Professor Bob Snow and Abdisalan Noor of the Kenya Medical Research Institute-Wellcome Trust Programme and University of Oxford.