On Feb. 1, the World Health Organization declared the spread of Zika virus across Latin America a “public health emergency of global concern.” Zika is a mosquito-borne virus related to the dengue and yellow fever viruses. In most cases, infection by Zika has no symptoms, which means the disease is usually not diagnosed. Only 20 percent of Zika cases are accompanied by symptoms such as fever and rash. The disease, which originated in Brazil, has spread to almost 30 other countries and territories, including the United States, where at least 82 cases have been reported.
The real danger of Zika occurs when a pregnant woman contracts the disease. The Zika virus is associated with the birth defect microcephaly, in which infants are born with smaller-than-normal heads. Microcephaly can cause a range of health issues such as seizures, developmental delays and hearing and vision problems. Though scientists are not completely certain Zika causes microcephaly, mounting evidence suggest a link between the two. While the Zika virus is transmitted through mosquito bites, climate change could be the real driver of this outbreak.
Climate change is typically associated with rising sea levels and extreme weather. But our warming climate may also make it easier for certain diseases to spread, particularly those transmitted by mosquitoes. The insects need warm temperatures to survive and standing or slow-moving water to reproduce. Climate change’s increased rainfall and higher temperatures can combine to make it easier for mosquitoes to extend their life spans and increase the areas where they can survive. This means that Zika can travel farther and outbreaks can last longer because the mosquitoes that spread the disease are more viable.
Zika is not the only disease that can benefit from climate change. In 1999 researchers estimated that 320 million more people would be at risk for malaria in 2080 because of climate change, in large part because mosquitoes are able to survive longer in warmer climates. In 1998 researchers predicted that climate change would increase the potential for a global dengue fever epidemic by nearly half. While we have yet to see a global dengue epidemic, the disease is spreading to areas where it was rarely seen before. On Feb. 8, the mayor of Hawaii County declared a state of emergency due to an outbreak of mosquito-borne dengue fever. Hawaii had more than 250 confirmed cases of dengue since September 2015.
Chikungunya, another mosquito-borne virus, could be following the same pattern. Before 2006, chikungunya was rarely identified in the United States, but in 2014 and 2015, more than 3,400 cases were reported to the Centers for Disease Control and Prevention.
Biologists and the WHO have warned that the Zika outbreak is the tip of the iceberg, suggesting that the virus will linger as long as the global climate continues to heat up. To be clear, not everyone agrees. Some researchers have questioned the models used to make the predictions about increase of disease due to climate change, arguing that the projections don’t take into account factors such as local climates and mosquito biology and that global warming will have a mixed effect on mosquitoes and the diseases they carry. But there appears to be a broad consensus on the fact that global warming creates better conditions for mosquito-borne illnesses. The main difference appears to be on how much worse things will be.
There are simple ways to control mosquitoes, including through pesticides and bed nets. The problem with the Zika epidemic is not that we cannot contain it but that it has been a long time since the U.S. dealt seriously with a mosquito-borne illness. If the U.S. government responds to this emerging threat at the same leisurely pace at which it initially approached climate change, the disease could become endemic.
Fighting mosquitoes and the illnesses they transmit is an important first step, but we should not focus on treating symptoms while ignoring their cause. The U.S. must address climate change in order to eliminate the increased risk of mosquito-borne illnesses. In December, President Barack Obama and other world leaders took a step in the right direction when they agreed to curb carbon dioxide emissions at the United Nations climate change conference in Paris.
The two Democrats vying to replace him — former Secretary of State Hillary Clinton and Vermont Sen. Bernie Sanders — have laid out plans to build on the Obama administration’s accomplishments. Republican candidates, by contrast, have either downplayed the severity of climate change or denied its existence.
If the current Zika virus and dengue fever outbreaks are the health consequences of climate change, while Obama’s actions on climate change — including the Paris agreement and his Clean Power Plan — won’t solve the problem, they may contribute to slowing it down. We need a president who can continue to build on that progress. However, if the American people elect a climate change denier in November, Zika and other mosquito-borne illnesses could become a permanent part of American life, along with the host of other plagues from climate change.