The Interrelated Factors of Climate Change and Pandemics

Pandemics have afflicted mankind for millennia. Diseases like Spanish flu, smallpox and bubonic plague have ravaged humanity throughout its existence often changing the course of history. From SARS in 2003, H1N1 influenza “Swine Flu” in 2009, Chikungunya in 2014, Zika in 2015 to Ebola outbreaks in Africa over the past 7 years, pandemics continued to threaten human populations across the globe.

COVID-19

SARS-CoV-2 was first reported as cases of atypical pneumonia in Wuhan which spilled over from a bat or other animal into humans in initial outbreaks linked to animal and seafood markets in the city. As of June 2021, SARS-COV-2 is reported to have infected over 180 million people and caused almost 4 million deaths globally. The COVID-19 pandemic has had devastating health, social and economic impacts on human populations worldwide with the potential for long term effects years after the immediate health threat has passed. Current projections suggest the global economy will decline approximately 8%¹ leaving many countries in or at the brink of recession as a result of the pandemic.

The COVID-19 pandemic has shown how vulnerable we are to pandemics despite major improvements in life expectancy and the technological advances of the past century. International public health experts have stated that the risks of new pandemic-prone diseases are higher now than at any other point in history. The reasons for this are related to interconnected risk factors and drivers for disease emergence, amplification and spread which includes climate change. Other risk factors include deforestation and widespread changes to land use, intensive farming, and expansion of global travel and trade. Increasing urbanisation and high population densities in cities, and the increasing frequency and severity of natural disasters associated with climate change and subsequent human displacement² are additional risk factors which offer infectious diseases multiple opportunities to emerge and spread among human populations.

Climate Change

Deforestation is the largest cause of habitat loss worldwide. Loss of habitat forces animals to migrate and potentially contact other animals or humans causing spill over events. Deforestation has been shown to alter the natural circulation of viruses and change the composition, abundance, behaviour and possibly viral exposure of reservoir species. This has been shown to increase contact between infected animals and humans. According to EcoHealthAlliance, deforestation is linked to 31% of emerging disease outbreaks such as the Ebola, Zika and Nipah viruses³. The origin of the Ebola outbreak in West Africa in 2014 has been traced to the remote Forest Region of Guinea where much of the surrounding forest area had been destroyed by international mining and timber operations⁴. Evidence suggests that the resulting forest loss, estimated at more than 80%, brought potentially infected wild animals, and the bat species thought to be the virus’ natural reservoir, into closer contact with human settlements. The first case was in an 18-month-old child who was reported to have been playing in his backyard near a hollow tree heavily infested with bats.

Large livestock farms can serve as a source for spill over infections from animals to people. Avian influenza remains the most likely source of the next pandemic. Intensive poultry farming practices increase the risk of transmission to poultry workers and further spread among human populations. Reducing demand for animal meat and supporting more sustainable farming could decrease emerging infectious disease risk and lower greenhouse gas emissions.

Climate change has had a direct impact on the risk of disease emergence and importation of vector borne diseases. Global warming has led to hotter climates with higher levels of precipitation in northern latitudes. As the planet heats up, increased temperatures allow mosquitoes, ticks and other disease-carrying insects to proliferate, adapt to different seasons and invade new territories. Outbreaks of vector borne diseases have occurred in Europe including dengue in France and Croatia, malaria in Greece, West Nile fever in south-east Europe and chikungunya in Italy and France. Recent outbreaks of the West Nile virus in the USA and chikungunya virus in the Caribbean and Italy highlight the importance of assessing future vector-borne disease risk.