The largest repository of any parasitic disease in the world - a collection of malaria survey data in Africa – has been unveiled by researchers at the Kenya Medical Research Institute and the Wellcome Trust. The collection covers more than 50,000 surveys spanning 115 years since 1900, each documented by date, geolocation, number of people, and the proportion positive for Plasmodium falciparum infection.
The researchers analysed the data to estimate malaria infection prevalence for each of 520 administrative units of Sub-Saharan African Countries and Madagascar for 16 time periods since 1900 through to 2010-2015.
The biggest historical drops in malaria followed the Second World War with the discovery of DDT and chloroquine, and later in 2005 with the rolling out of insecticide treated bed nets and new drugs to treat malaria.
Malaria prevalence was low during the late 1960s, through the 1970s and early 1980s. This was a period when, despite the international community abandoning 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 the perfect lull in malaria transmission.
‘People often focus on recent history in tracking malaria in Africa, to inform donors and control programmes on recent actions,’ says the study’s lead author Professor Bob Snow of Oxford’s Centre for Tropical Medicine and Global health. ‘The longer history of malaria in Africa allows us to put into context the recent decline.’
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.
It took a further five years for the international community to provide free insecticide treated bed nets and effective malaria treatments. The financial response by the Global Fund and the technical revisions to policy by the World Health Organisation after 2005 led to one of the largest drops in malaria infection prevalence witnessed since 1900.
Co-author, Abdisalan Noor of the Kenya Medical Research Institute/Wellcome Trust Research Programme (KEMRI-WTRP), adds: ‘Shown in context, the cycles and trend over the past 115 years are inconsistent with explanations in terms of climate or deliberate intervention alone. The role of socio-economic development, for example, remains poorly understood.’
The current prevalence of infection, 24%, is at its lowest in 115 years but gains have stalled since 2010 and 240 million infected individuals remains a substantial burden. Little has changed in the high transmission belt across West and Central Africa. Emerging insecticide and drug resistance remain a threat, along with growing international ambivalence to funding control.
‘The history of malaria risk in Africa is complex, there have been perfect lulls when drugs worked and droughts prevented mosquito’s transmission infection; there have been perfect storms when drugs stopped working and flooding affected large parts of Africa,’ adds Snow. ‘It has been a history of long term cycles and predicting the future of malaria in Africa based on climate or intervention coverage alone is difficult.’