Aside from being largely responsible for the almost constant occurrence of natural disasters on often vulnerable communities, climate change also has the ability to cause outbreaks of infectious diseases like Zika, malaria and dengue fever, according to a new study by researchers at the University of Colorado Anschutz Medical Campus.
The role of environmental variables and climatic conditions in shaping human health has been recognized for centuries. Infectious diseases, in particular, may be sensitive to climatic conditions through their effects on abundance of vectors such as mosquitoes, ticks, and other disease-carrying insects.
Cecilia Sorensen, MD, lead author of the study and the Living Closer Foundation Fellow in Climate and Health Policy at CU Anschutz, explained that when natural disasters strike such places, the climatic conditions could make the public health crisis significantly worse.
“Climate change presents complex and wide-reaching threats to human health. It can amplify and unmask ecological and socio-political weaknesses and increase the risk of adverse health outcomes in socially vulnerable regions.”
The researchers said these vulnerabilities exist on virtually all corners of the planet. In the entire southeast region of the United States, cases of West Nile disease doubled in the year following Hurricane Katrina. Climate change in Africa appears to be increasing cases of malaria. And the recent destruction in Houston, Florida and Puerto Rico due to hurricanes will likely bring about more infectious diseases in the years ahead.
The study also pointed how the earthquake that struck coastal Ecuador in April 2016, coincided with an exceptionally strong El Niño event. El Niños are commonly associated with heavy rainfall and warmer air temperatures. They are also linked to outbreaks of dengue fever.
In addition to that, the study also found that an increase in water scarcity after the earthquake indirectly benefited mosquito development. The earthquake caused serious damage to municipal water systems, forcing people to store water in open containers outside their homes. These served as additional habitats for mosquito larvae.
Sorensen, who is a clinical instructor in emergency medicine at CU Anschutz, was in Ecuador with her co-authors working with the Walking Palms Global Initiative. They were operating a mobile health clinic after the disaster, and she spoke about what they were able to observe.
“We were seeing all of these viral symptoms in the wake of the quake,” she said. “We noticed a huge spike in Zika cases where the earthquake occurred. Prior to this, there were only a handful of Zika cases in the whole country. In fact, the researchers found the number of Zika cases had increased 12-fold in the quake zone.”
Zika virus is transmitted by mosquitos. Symptoms are usually mild, but the infection can cause major abnormalities and even death in a developing fetus.
Sorensen is among those who believe warmer temperatures and increased rainfall from the El Niño, along with a decimated infrastructure and an influx of people into larger cities, is likely what led to the spike in Zika cases.
“We saw so many people affected by the earthquake that were sleeping outside without any shelter from mosquitoes, so we were worrying that the region’s changing climate could facilitate the spread of diseases,” she said. “Natural disasters can create a niche for emerging diseases to come out and affect more people.”
Sorensen’s team reviewed the research they had on file regarding the connection between short-term climate changes and disease transmission. They applied those findings to explain the role of the earthquake and El Niño in the Zika outbreak.
The researchers suggest El Niño created conditions Zika-carrying mosquitos need in order to breed and make more copies of the Zika virus. The warmer temperatures and increased rainfall from El Niño have previously been associated with a higher likelihood of dengue outbreaks. Warmer temperatures can also cause faster viral replication in mosquitoes and influence their development and breeding habits.
At the same time, the El Niño event brought with it warmer sea-surface temperatures, which have been shown to go hand-in-hand with outbreaks of mosquito-transmitted diseases. Estimates from remote sensing data in coastal Ecuador show that sea-surface temperatures were higher than average from 2014-2016.
Sorensen is hopeful that governments will use these new findings in the future to identify and protect vulnerable communities before natural disasters happen.
“One idea is to develop disease models that can use existing climate models to predict where these vectors will show up due to climate variability,” she said. “Applying these new models to areas that have pre-existing social vulnerabilities could identify susceptible regions, allowing us to direct healthcare resources there ahead of time.”
[Featured Image by Rodrigo Abd/AP Images]