Thomson Reuters Foundation, trust.org (TRF)
By Alex Whiting
Health agencies in Africa need to start consulting seasonal weather forecasts to help prepare for malaria epidemics and ensure outbreaks are spotted early and curbed before they become severe, a malaria expert said.
Rising temperatures, floods and droughts can cause major epidemics in areas not usually affected by malaria, particularly as people may lack immunity to the disease and are therefore more likely to fall ill or even die, said Tarekegn Abeku, senior technical specialist at international non-profit Malaria Consortium.
Weather forecasts are vital to help health agencies know where to increase vigilance "so that if there is an outbreak you can take action immediately", he told the Thomson Reuters Foundation from his London office.
Forecasters are getting better at predicting these threatening weather patterns - sometimes months in advance - as they become more frequent and more severe in many countries as the climate changes.
But currently most health agencies in Africa have "no organised way of looking at information related to climate change", said Abeku.
"Most malaria epidemics follow abnormal weather conditions, often in combination with other causes, including increased resistance of the parasite to antimalarial drugs," he said.
In the last 60 years in Ethiopia, for example, most outbreaks have been associated with El Nino or La Nina weather patterns, which can bring higher temperatures, more rainfall or drought, Abeku said.
In one of Ethiopia's worst outbreaks, an estimated 3 million people were infected and 150,000 died when malaria spread to the country's highlands in 1958 because of unusually high temperatures.
The country's last major epidemic was in 2003 and was preceded by El Nino.
Experts expected another outbreak after the 2015/16 El Nino which brought high temperatures and drought to southern and eastern Africa - but it has not yet materialised, said Abeku.
Globally, there were 212 million new malaria cases in 2015 and some 430,000 people died of the disease. The vast majority of cases - 90 percent - of cases were in Africa, according to the World Health Organization (WHO).
Flooding in arid areas creates breeding grounds for malaria-carrying mosquitoes. Drought or higher temperatures in normally wetter areas also can be a threat if rivers and streams dry out and form pools of stagnant water.
As the planet warms, areas at risk of malaria are growing as mosquitoes spread to highland areas - and these areas need vigilant attention, said Abeku.
"This effect has been seen in South America and in Africa. When there is an increase in temperature there is an increase in the geographic coverage of malaria," he said.
Mosquitoes bite more often when it is hotter, he said. They also develop from eggs - which are laid on water - more quickly when water is warmer.
If the average temperature in an area rises from 21 degrees to 26 degrees Celsius, infection levels can increase because the time it takes for the malaria parasite to develop in the mosquito is halved to about 11 days, Abeku said.
But if temperatures rise as high as 30 or 35 degrees Celsius, the survival rates of both the mosquito and parasite fall, he said.
Although the changing climate and a warming planet can create better conditions for malaria, its spread can still be curbed by better housing, education and health care, and increased urbanisation.
Malaria mosquitoes do not like the polluted water found in towns and cities, Abeku said, and Africa is urbanising rapidly - its urban population doubled between 1995 and 2015, according to African Economic Outlook 2016. But one mosquito's pain is another's pleasure, and the mosquitoes that carry dengue, Zika, lymphatic filariasis and other viruses thrive in urban areas and the breeding grounds they offer, Abeku said.
Anti-malarial interventions over the last 15 years, including the roll out of insecticide-treated bednets, indoor insecticide spraying and better malaria drugs in Africa, have played a major role in cutting malaria infections, he said.
Between 2000 and 2015, the number of new cases in Africa fell by 42 percent and death rates fell by 66 percent, WHO said.
The interventions - from bednets to better housing - all help counter potential rises in infections as a result of climate change, he said.
"That is probably why in countries like Ethiopia we haven't seen a major epidemic (after) the 2015 El Nino," Abeku said. But "that doesn't mean this effect will continue".