How Climate Change is Fueling Health Risks and Infectious Diseases - Dr Subramanian Swaminathan

The change in climate has been most sharply perceived by the current inhabitants of Earth compared to prior generations. There has been an overall uptick in temperatures, but also changes in rain pattern and other ecological disasters. These have heavily influenced the infection related risks to humans.

The Intergovernmental Panel on Climate Change is confident that the health threats worldwide will worsen with climate change. The life cycle of many infectious agents are related to climate, and the effects are already evident.

Rise in temperature and changes in precipitation changes the range of disease bearing vectors like mosquitoes, fleas, ticks, and birds, which can cause outbreaks of many diseases like dengue, malaria, Chikungunya, and Zika.

With warming, vectors are able to survive winters, infections like dengue and Zika are spreading to temperate countries. With habitat disruption, wildlife-human interaction has increased, accounting for spill over infections like Nipah, hanta virus and Ebola.

This problem has been compounded by increasing repurposing of land which was originally forest, making humans live very close to vectors and pathogens.

Storms and flooding have caused outbreaks of leptospirosis, typhoid, Shigellosis, gastroenteritis, hepatitis and skin diseases among many other diseases as well. With cycles of drought and flooding, livestock are often moved around in nomadic communities, making them vulnerable to diseases like anthrax and viral haemorrhagic fevers.

Climate changes can positively influence pathogens and vectors. For example, warmer temperature increases mosquito population, their survival, their biting rates and viral survival, increasing the ability of West Nile virus to transmit.

This is considered an important reason for this virus sweeping many parts of the New World 2 decades ago. Ocean warming with heavy rains reduces salinity of coastal water, which facilitates growth of Vibrio species, including cholera.

Hotter temperatures the ability of Vibrio species to transmit, survive and cause injury to humans. In fact, there may a selection of more heat-resistant viruses, which can better cope with our primary defence mechanism during an infection-our ability to generate a fever.

In addition to this, climatic conditions also make us less effective in facing the challenge. There is additional stress from such situations, which may make people more vulnerable. There is displacement into unsafe conditions, which can result in outbreaks, like, the cholera outbreak in Haiti.

Breakdown of facilities and services increase the risk of exposure to pathogens and, coupled with poor availability of healthcare services, can be deadly. During times of catastrophe, nutrition can also be poor, which can result in a vulnerable and under functioning immune system.

The other half of this is the possibility of the re-emergence of ancient diseases which are now extinct. Analysis of ice cores from the permafrost in the Antarctic and Siberia have shown pathogens from the distant past which are no longer around today.

With increased and rapid melting of these ice caps, such pathogens could be released, and we may have no effective immunity against such challenges.

In fact, genetic analysis of an anthrax outbreak from the arctic circle suggests that the strain is rather ancient and likely from an animal carcass which became exposed as the ice over it thawed. This specific concern has been likened to a Pandora’s box.

Of note, there are pathogens which are likely to be less of a challenge with climate change, like, influenza, SARS, COVID-19, rotavirus etc, but other hazards like human behaviour may still balance it out. Further, for every pathogen that is expected to reduce, many times more infections are potentiated.

The burden of such changes is hardly equal- it affects the marginalized and poorer sections disproportionately more. The climate and health council of the United Kingdom has made recommendations, many of which could be relevant to us.

Energy audits, water conservation, reducing emissions, waste reduction and safe disposal along with increasing native vegetation could help significantly. Public health measures like the Swachh Bharat initiative will help to some extent, but without more concrete measures, we are in for a bumpy ride.