Zika Outbreak 2014 - 2017
On July 29, 2016, Florida and federal officials confirmed the first local spread of the Zika virus through infected mosquitoes in the continental United States. As of April 5, 2017, the World Health Organization reported 223 confirmed, locally transmitted Zika cases in the US, as well as 5,393 imported cases. In Brazil, the worst hit country, there have been 131,643 confirmed cases, 219,280 suspected cases, and 2,542 instances of microcephaly and other central nervous system birth defects. A November 2016 attribution study finds that the risk of Zika transmission was higher in 2015 than at any time during the 1950-2015 period, and that the Zika outbreak was very likely fuelled by unusually high temperatures — a result of a very strong El Niño event on top of ongoing human-caused climate change.[1] Climate change creates new risks for human exposure to vector-borne diseases such as Zika, particularly in the United States where rising heat and humidity are increasing the number of days annually in which disease vectors thrive. In the United States, 76 percent of major cities have seen an increase since 1980 in days conducive for mosquitos.
Zika outbreak in the United States and South America triggers climate concerns
The Zika outbreak of 2014 was caused by a tropical virus spread by Aedes mosquitoes, as well as through sexual contact with an infected person. The disease has been linked to an increase in miscarriages, deaths in newborns, and birth defects, especially a condition known as microcephaly, in which the brain does not fully develop and babies are born with abnormally small heads.[1]
Zika virus may also put adults at risk.[2] An August 2016 study looking at the effect of Zika infection on the adult brain suggests that adult brain cells responsible for replacing lost or damaged neurons throughout adulthood, cells that are likely critical to learning and memory, may be vulnerable to infection.[2]
On July 29, 2016, Florida and federal officials confirmed the first local spread of the Zika virus through infected mosquitoes in the continental United States.[3]
As of April 6, 2017, the World Health Organization reported 223 confirmed, locally transmitted cases, 5,393 imported cases, and 63 confirmed congenital syndrome cases associated with Zika.
| Country | Suspected | Confirmed | Imported | Birth Defects |
| United States | 0 | 223 | 5,393 | 63 |
The threat of explosive, local transmission like that seen across South and Central America, however, remains low.[4]
In Brazil, the worst hit country, the Ministry of Health estimated that there have been 131,643 confirmed cases, another 219,280 suspected cases, and 2,542 cases of birth defects.
| Country | Suspected | Confirmed | Imported | Birth Defects |
| Brazil | 219,280 | 131,643 | 0 | 2,542 |
In all, 45 countries and territories have confirmed local, vector-borne transmission of Zika virus disease in the Americas since 2015.[5]
The spread of the Zika virus has many concerned about the impacts of infectious diseases in a warming world. The Commission on a Global Health Risk Framework for the Future issued a report in January 2016, which shows that many countries are unprepared for the increased threat of these diseases.[6] Mosquitoes, which carry a variety of major infectious diseases, thrive in warm, wet climates. With global temperatures rising and increased flooding due to climate change, the spread of mosquitoes and the diseases they carry is likely, scientists say.
Climate change creates new risks for human exposure to vector-borne diseases such as Zika
A November 2016 attribution study looks at the Zika outbreak in 2015 in South America and finds that the combination of a strong El Niño event and human-caused climate change created optimal conditions for the outbreak.[7]
Climate change creates new risks for human exposure to vector-borne diseases by altering conditions—such as local temperatures, rainfall amounts, and warm season length—that affect the development and spread of disease vectors and the pathogens they carry.
As temperatures warm, mosquitoes and other warm-weather vectors can move into higher altitudes and new regions farther from the equator. Rising global temperatures can also lengthen the season during which disease vectors thrive and increase the geographic range of disease-carrying insects.
A July 2016 analysis by Climate Central finds that most major cities in the United States—an estimated 76 percent—have seen an overall increase in days conducive for mosquitoes from 1980 to 2016, and many regions have seen the mosquito season increase by half a month or more.[8] Florida cities face the greatest overall threat from mosquitoes. Most of its major cities face hundreds of days each year with climate conditions that are ideal for these insects.[8]
Increased rainfall, flooding and humidity can also create more viable areas for vector breeding and allows breeding to occur more quickly, as eggs hatch faster in hotter climates.
Climate change a factor in spread of ticks that cause Lyme disease
After increased reports of Zika virus raised concerns about climate change and infectious disease, an analysis published in January 2016 shows that Lyme disease-carrying ticks have spread significantly in the US and are now found in nearly half of all American counties.[9] Ticks are now found in twice the number of counties that they were in 1998, according to the US Centers for Disease Control.[9]
Climate change has contributed to the increase of the pests, with increased temperatures and rainfall aiding their spread. Milder winters have also contributed to the expansion of mammals and birds that the ticks feed on, allowing their population to grow. Since the late 1990s, the number of reported Lyme disease cases in the US has more than tripled.[9]
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