Infectious disease rates increase when more people are exposed to agents including viruses, bacteria, parasites, and fungi. COVID-19 most likely came from a virus present in wild bat species and this crossover (or zoonotic) infection is a direct result of interactions with wildlife and human expansion into wild habitats.
Climate change works to increase those interactions in another way: by allowing mosquitoes and other species to extend their range into new territory. In 2016, mosquito bite transmission of Zika virus–which causes birth defects and infant mortality, and can be fatal in adults–was discovered in Florida and Texas. The same mosquito species that spread Zika, also spread dengue virus.
Increases in average temperatures could mean that these diseases become established in more US states. The World Health Organization has analyzed the risks linked to environmental change and found that a global temperature increase in the range of two to three degrees Celsius exposes several hundred million more people to malaria. Other human-led environmental damage such as deforestation, or building into wild habitats results in higher risk of malaria and dengue too.
Mosquitos and a Warmer World
Climate change is cited for the introduction of West Nile virus to the US. West Nile is spread by the mosquito species Culex and finds a natural reservoir in birds. People become infected by mosquito bites and that can cause damage to the brain and central nervous system, or even death.
Research shows that Culex population growth is linked to higher temperatures, high humidity and drought. Approximately seven million people were infected in the US between 1999 and 2016. West Nile continues to spread into new territory, reaching as far north as Philadelphia and Connecticut.
Another factor increasing exposure is the warming of the Arctic. As permafrost melts in the Arctic Circle it reveals deadly bacteria previously frozen in the soil like anthrax, ancient viruses, and other poisons.
Disease control in the twenty-first century is sophisticated, but as we become increasingly connected we also open ourselves up to more outbreaks. No civilization throughout history has been immune and pandemic was a factor in the fall of the Roman Empire.
Stopping the Spread
If we do nothing then wider spread of Aedis aegypti and Aedis albopictus mosquitoes into North America and Europe will bring tropical disease to millions more. Vaccines and other medicines will need to be developed for these vector-borne infections, and vaccination rates for diseases like yellow fever in East Africa will need to vastly increase to avoid a projected increase in deaths of up to 25%.
One technology trialed to tackle vector-borne disease introduces genetically modified (GM) mosquitoes to eradicate local populations. Biotech company Oxitec released 450,000 lab-grown species to fight Zika virus in Jacobina, Brazil.
Genes in the OX513A mosquito were supposed to stop breeding, but despite having an initial impact, the population recovered and may have strengthened. Approvals for Oxitec to release 750 million GM mosquitoes in Florida starting in 2021 have been opposed as a ‘Jurassic Park experiment’.
Certainly, funding for research is essential to combat spread. The Centers for Disease Control couples practical advice on preventing bites with long-term funding to analyze disease trends and increase preparedness.
US government institutions are focusing on everything from health impacts to better pesticides to manage and reduce the effects of climate change. They are also trying to make agriculture more resilient and conservation friendly. Environmental signals are being built into the country’s infrastructure to try and lessen the burden of disease.