The hot zone: what the changing climate means for infectious disease: Simone Richardson

While the spread of exotic infectious diseases conjures up the image of scientists in hazmat suits running around the forests of Borneo, the threat, it seems, is much closer to home. It is becoming more apparent that climate change not only affects our natural resources; the availability of water, fertile land and extreme weather conditions, but it also affects the spread of disease. In addition to existing diseases popping up where we have not previously seen them, new and emerging outbreaks will also likely take hold. Climate change could result in differences in where, when and how often diseases appear. This means that as settings change to create conditions for the spread of debilitating and potentially fatal diseases (such as malaria, zika, and dengue), we will see higher rates of illness and death in previously unexposed populations.  

Diseases transmitted by insects are highly likely to be impacted by climate change. Breeding patterns of insect carriers are a significant indication of disease prevalence and increasing reproduction of these carriers are spreading diseases further than ever. More than 90% of malaria-related deaths occur in Africa, where humidity and tropical climate temperatures support the parasites’ life cycle. If global temperatures increase by 2 to 3°C, as expected, it is estimated that the population at risk for malaria will increase by 5%, equalling millions of additional new infections. As climate patterns shift, it is likely that new areas will become malaria endemic.  Malaria has appeared for the first time in the highly populated region of the highlands in east Africa due to increased temperature.

Climate change will likely affect other vector-borne diseases like dengue more complexly, with increases expected in areas where higher rainfall and humidity will enhance the breeding of mosquitoes. However, Aedes mosquitoes typically breed in water containers used for household storage, a system which might be implemented in times of drought. Similarly, tick-borne diseases such as Lyme disease have nearly doubled in the United States, with shorter winters sighted as the main reason.

Climate change is also lending a helping hand to water-borne pathogens that flourish in warmer waters. Increased rainfall affects flooding, sanitary conditions and the spread of diarrhoeal diseases including cholera. It is predicted that by 2030 there will be 10% more diarrhoeal disease than there would have been without climate change and it will primarily affect the health of young children. Salmonella and other food-borne diseases have been linked to increasing temperatures, a problem that could be exacerbated in low income countries.

In addition to direct impacts on health, population displacement and food insecurity as a result of climate change are also having a big impact on disease spread. For the first time severe drought has been linked to increased HIV rates among women in Lesotho. Young women in the drought affected areas were more likely to have transactional sex and have earlier sexual debut. In times of food insecurity, families are likely to adapt extraordinary measures to guarantee food, which often leads to changes in disease incidence. The effectiveness of antiretroviral drugs in the face of a food shortage and malnutrition is also a concern, with uncontrolled HIV infection resulting in increased transmission. Sexually transmitted infections (STIs) in general are associated with population displacement, risk-taking behaviour and poverty- all of which may be enhanced by climate change. Despite this, climate change policies do not typically include efforts to enhance STI prevention.

The World Health Organisation has determined that although climate change is far reaching, developing regions have and will be disproportionately affected even though greenhouse gas emissions are largely attributable to developed countries. This includes the United States, which has pulled out of the Paris accord – an agreement to lower emissions and the average temperature of Earth. President Donald Trump stated “The Paris accord will undermine [the U.S.] economy,” and “puts [the U.S.] at a permanent disadvantage”. This statement has put the reduction of emissions at risk. Governments play a crucial role in mitigating climate change because these international agreements form the basis of the policies that will directly impact health, with weak public health institutions likely bearing the worst of climate change effects. We should view the effect on infectious disease as a new indication that climate change will affect us in unexpected and unwelcome ways should we not have policies and interventions in place by the time South Africa is firmly in the hot zone.

About the author

Dr Simone Richardson is a post-doctoral fellow at the National Institute for Communicable Diseases where she focuses on understanding how antibodies can prevent viral infections like HIV and influenza. She hopes that the work she does will help to develop more effective vaccines!

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