Outbreaks of Infectious Diseases Due to Climate Change

A new study by researchers from the University of Colorado Anschutz Medical Campus, says that apart from causing devastating natural disasters on helpless communities, climate change can also provoke the outbreaks of infectious diseases such as malaria, Zika, and dengue fever.

The lead author of the study, Cecilia Sorensen, MD, who is also the Living Closer Foundation Fellow in Climate and Health Policy at CU Anschutz says that complicated and wide-reaching threats are posed by climate change to human health. She says, it can accelerate and expose socio-political and ecological weaknesses, and increase the risk of adverse health results in socially vulnerable (i.e., low income) areas. According to her, when natural disasters affect such regions, the climatic conditions may significantly worsen the public health crisis.

The scientists say that these vulnerabilities can occur anywhere. For instance, an year post the Hurricane Katrina in New Orleans, there were doubled incidences of West Nile disease; the increasing incidences of malaria in Africa is owed mostly to the climate change there; and it is expected that the recent hurricanes in Puerto Rico, Florida and Houston may bring more infectious diseases in the upcoming years.

The current study concentrated particularly on a 7.7 magnitude earthquake which in April 2016 hit Manabi in coastal Ecuador, and coincided with an unusually strong El Niño event, which ushers warmer air temperatures, heavy rainfall, and dengue fever outbreaks. The devastation was huge. The USAID (United States Agency for International Development) reported 9,750 damaged buildings, 40 missing persons, more than 30,000 displaced people, 660 fatalities, 4,605 injuries, and 720,000 people in need of humanitarian assistance.

Sorensen, a clinical instructor in emergency medicine at CU Anschutz, who was operating a mobile health clinic in Ecuador along with her team, post the disaster said “We were seeing all of these viral symptoms in the wake of the quake. 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.”

The scientists, in fact, found that the incidences of Zika had increased 12-times in the zone of the earth quake. Zika is a mosquito transmitted viral disease, whose symptoms are generally mild, but the infection can incur anomalies and even fatality in a developing fetus. The likely causes of the spike in Zika incidences, according to Sorensen, were increased rainfall and warmer temperatures from the El Niño, and a destroyed infrastructure and an inrush of people into larger cities.

Many earth-quake affected people were sleeping in open air without any protection from mosquitos. This facilitated the disease’s spread. Thus, natural disasters can enable emerging diseases to affect more people.

The current research on the association between short-term climate changes and transmission of disease was reviewed by Sorensen’s team. They explained the role of El Niño and the earth quake in the outbreak of Zika by applying those findings.

They propose that El Niño created ideal breeding conditions for Zika-carrying mosquitos, and the replication of Zika copies in them. El Niño’s increased rainfall and warmer temperatures have been earlier linked with an increased likelihood of dengue outbreaks. Further, warmer temperatures could have induced mosquito breeding and also could have accelerated viral replication in them.

Simultaneously, the El Niño event ushered warmer sea-surface temperatures, which corresponded with bursts of mosquito-transmitted diseases. Remote sensing data estimates in coastal Ecuador show higher than average sea-surface temperatures in the period between 2014 and 2016.

The scientists also suspect that the increased water scarcity following the earthquake too led to the mosquito development. Further, since the quake destroyed the municipal water systems, people were forced to store water in unclosed containers outside their houses. These added to the habitats of mosquito larvae.

Thus, the abnormal climatic conditions coupled with an earthquake in an area with social vulnerabilities multiplied the Zika outbreak.

In the modern era, climate change is emerging as one of the biggest threats to human health. Governments can derive from these research findings to identify and safeguard vulnerable communities before the occurrence of natural disasters said Sorensen.

She said “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. 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.”

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