Zika virus linked to microcephaly epidemic in Americas
The mosquitoes that carry Zika are now spread over an unprecedented portion of the earth due to the increasing temperatures, deforestation, and this year’s El Nino event, the largest in history. Amidst the international panic over the appearance of Zika virus in the Americas for the first time ever and a correlated spike in cases of microcephaly or babies being born with abnormally small heads, the effects of climate change on infectious disease are once again in the international spotlight.
On 2nd February, WHO declared Zika virus a public health emergency, seeking to build and coordinate a large-scale, global response. As of 2nd January, Brazil had reported 3,174 cases of microcephaly, including 38 related deaths in 2015. This represents a twenty-fold increase over 147 cases reported in 2014. In adults, the signs and symptoms of Zika virus are generally mild and could be confused with the common flu. Very rarely, it can also cause Guillain-Barré syndrome, a neurological disorder that can have serious effects including paralysis.
Laurie Garrett from the Council on Foreign Relations (CFR) has pointed out that though Koch’s Postulates have not been put to test in proving that Zika is the definitive cause for this dramatic spike in cases of microcephaly, there are strong indications that this is the case; the correlation between the increase in microcephaly and the spread of the virus’s territory is extremely convincing and Zika has been found in the amniotic fluid of mothers carrying babies with microcephaly.
The species of mosquito acting as a vector for Zika, Aedes aegypti, was the target of widespread eradication efforts in the Americas in the 1950s after it was found to spread both yellow fever and dengue, but these efforts were mostly reversed in 1997 by the El Nino event (which is the largest on record until this year). Record rainfall created pools of standing water that served as breeding grounds for mosquitoes causing resurgence of mosquito population and disease.
Today, the secondary effects of large-scale deforestation further complicate vector control efforts. Research by Dr. Deborah Lawrence from the University of Virginia shows how forests can help to regulate weather patterns and help topsoil to soak in rainwater. This causes standing puddles of rain water, which become major breeding grounds for A. aegypti. The current winter months are in fact the most dormant period of the year for the mosquitoes, so as temperatures rise and mosquito activity increases, both the insect and the diseases it carries are likely to become even more widespread.
The emergence of Zika recalls the spread of chikungunya across the Americas since 2005, which in turn seems to have followed the initial spread of dengue in the same area in the early 2000s. Both of these viruses are also carried by A. aegypti and are surging in South and Central America in the wake of the current El Nino event. The more aggressive and hardy tiger mosquito (Aedes albopicus) has also emerged and spread across the Americas, first appearing in the US during the summer of 2015, and is projected to benefit greatly from increases in rainfall and temperature. Both chikungunya and dengue successfully mutated to be carried by A. albopicus, which has amplified their geographic reach. Zika is likely to mutate in the same way to be carried even farther and infect more people through the tiger mosquito.
Government actions in response to the Zika epidemic include: a CDC travel advisory for pregnant women which now covers 22 countries in Central and South America, and the Caribbean; advisories to delay pregnancy until the outbreak is controlled in Brazil and Colombia; and a strong recommendation by the government of El Salvador to avoid getting pregnant until at least 2018.
Dr. Anthony Fauci, head of the US National Institute of Allergy and Infectious Diseases, has said that developing a vaccine is a major priority for the agency, although it may not be ready for release in time to have a major impact on the current epidemic. He said in an interview with TIME, “Things like this tend not to go away. [Cases] may go up and down, but it’s not just going to go away, so you need to start working on a vaccine now. It may be important in a year from now or six months from now, we don’t know.”
Sources for more information
Laurie Garrett’s January 25, 2015 newsletter, which is available at http://www.cfr.org/about/newsletters/onthefly.php?id=3493
WHO Zika factsheet at http://www.who.int/mediacentre/factsheets/zika/en/
PAHO Zika alerts and updates at http://www.paho.org/hq/index.php?option=com_content&view=article&id=11599&Itemid=41691&lang=en
US CDC Zika virus pages, including travel advisories at http://www.cdc.gov/zika/index.html
Deborah Lawrence’s research on global warming and skewed rainfall, summarized by this NewsWise article: http://www.newswise.com/articles/peer-reviewed-report-clearing-tropical-rainforests-distorts-earth-s-wind-and-water-systems-packs-climate-wallop-beyond-carbon
Reuters ongoing coverage, most recently in this in-depth article at http://www.reuters.com/article/health-zika-who-idUSKCN0VA39E