Will extreme climatic conditions undermine disease control measures?

Only a minor alteration in temperature amounting to 0.5C could lead to devastating climatic conditions including floods, drought, extreme heat and poverty - the world’s leading climate scientists have recently warned.

icddr,b study looks at a cholera endemic area in Bangladesh for over 26 years. Photo: GMB Akash / icddr,b

The UN Intergovernmental Panel on Climate Change (IPCC) has recently released a report noting that the world is currently 1C warmer than pre-industrial levels and it may be inevitable that this increases to 1.5C.

They point out that further fluctuation leading to 2.0C might lead to greater water stress and climate-related poverty, which will particularly affect the world’s developing countries. They urged the limitation of the use of fossil fuels to avert further environmental harm.

The effects of global warming are not just limited to melting glaciers or water stress. The World Health Organization (WHO) is among to suggest that there is a link between extreme climate conditions and infectious disease outbreaks. Scientists including infectious disease experts at icddr,b have already explored why climatic conditions may give rise to incidences of disease outbreaks as rising sea levels engulf more land.

A more recent study with icddr,b and collaborators from University of North Carolina and Johns Hopkins University, USA have examined the influences of heatwaves, rainfall and tree cover on cholera - the deadly diarrhoeal disease known for its heavy human death toll worldwide. Heatwave conditions are increasingly warming daytime temperatures and bring fewer cold days, which are widely considered to be triggered by climate change.

 Graphics from original study

Published in the Environment International, the new study looked at a cholera endemic area in Bangladesh for a period of over 26 years and suggested that the risk of cholera was higher two days after heatwaves had taken place.

“The relationship is not entirely simple and linear,” observes Dr Muhammad Yunus, icddr,b emeritus scientist and one of the authors of the study. “We have seen that the association between the risk of cholera and heatwaves was not significant for households with more medium-dense tree cover,” he comments.

Nevertheless, there are reasons to believe that heatwaves may promote cholera occurrence during rainfall and the beneficial effects of tree cover had a mitigating role to play.

Extreme climatic conditions are clearly connected to deforestation. Health scientists are examining how the overall impact of these aggravating environmental conditions are leading to many unpleasant health consequences including more frequent disease outbreaks.

The findings are doubly important in terms of the clear linkages to global warming because following the release of the recent IPCC report, scientists have predicted that keeping warming to 1.5C rather than 2.0C would significantly cut the risk of heatwaves and heat-related mortality among other extreme weather events.

The importance of water, sanitation and hygiene (WASH) measures and timely immunisation to avert cholera outbreaks are well-known. Endemic areas across the world have benefited from their appropriate application but the climatic effects on disease outbreaks are beyond these ground-level measures. It is time now that these are successfully mitigated as recognised by the global consensus on climate action before the successes around disease outbreak control are undermined by an unchecked rise in infectious diseases.

Muhamamd Zahir Hassan Nabil