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Zika virus and climate change

  • This post is a commentary. The views expressed are those of the author alone.
  • Why has Zika virus all of a sudden spread throughout the Western Hemisphere?
  • Climate change did not produce the Zika virus. But the Aedes aegypti mosquito can only survive in the right climatic conditions in the right environment, and its favored place to live is spreading due to climate change.

Zika virus is transmitted by a mosquito, Aedes aegypti. Mosquitoes breed in stagnant ponds. One adult Aedes mosquito can lay up to 1,000 eggs during her adult life of less than one month. She does this by flitting from place to place over time, depositing the eggs near the surface of the water. To stay alive, she feeds on blood. Male mosquitoes don’t suck your blood. The female uses the protein in blood to help make all of those eggs. The Zika virus is spread when she draws blood from an infected person and deposits the virus in an uninfected person. Her mouthpiece is very efficient and she does not transfuse blood. The Zika virus belongs to a family of viruses that include dengue fever, yellow fever, and chikungunya. A different type of mosquito, the Anopheles species, spreads malaria, which is a parasite, not a virus. Mosquitoes are quite adept at finding new places to live and eat, given that they have been around for millions of years. The Aedes aegypti mosquito that feasts on humans evolved from a type that sucked the blood from animals. Some time ago, a gene changed that enabled it to hone in on human scent to obtain blood for egg production. The disease-carrying mosquitoes transmitting dengue, yellow fever, chikungunya, and Zika virus specialize in attacking humans.

Aedes aegypti
Aedes aegypti

Why have Zika virus, dengue fever, and chikungunya spread into new locations over the last decade, while yellow fever has not? What is going on? Yellow fever caused more casualties during the Spanish-American War than did bullets and cannon balls. The Rockefeller Foundation declared war on yellow fever around the beginning of the 20th Century. They established a Yellow Fever Institute in 1936 in Uganda, and the next year, Dr. Max Theiler, working at the Rockefeller Institute in New York discovered a vaccine to prevent the spread of yellow fever. In 1951, he was awarded the Nobel Prize in Physiology and Medicine for his discovery. The Yellow Fever Institute has been renamed and relocated a short distance, but it began as a building in the Zika Forest, about 23 km south of Kampala. In 1947, scientists at the research lab isolated a new virus that they named “Zika virus”, after the forest, in the same way that Ebola virus was named after a river in the Democratic Republic of Congo where it was first uncovered. In 1952, the first documented case of Zika virus in people was detected in Africa.

Fifty-five years later, a Zika disease outbreak hit Yap Island, Micronesia, in the South Pacific. In 2013, residents of French Polynesia found themselves under attack by Zika virus. The disease only made headlines in 2015 after a massive outbreak in Brazil, along with an upsurge in the number of cases of microcephaly. In 1958, Brazil ended their national fumigation campaign to eradicate mosquitoes, after declaring victory over the insect. Then, shortly after the 2014 World Cup in Brazil, cases of Zika virus infection began to appear in patients coming to public hospitals. Up to 80% of people who are infected do not show symptoms, but, as with dengue and chikungunya, those showing symptoms suffer from high fever, muscle and joint pain, and possible skin rashes.

In early 2015, a confluence of devastating events rocked the medical community in Brazil. Between 2000 and 2014, Brazil recorded about 150 cases of microcephaly per year; in 2015, over 4,000 cases were confirmed. The nexus of the upsurge in cases was among poor women coming to public hospitals in Pernambuco, a state in the middle of Brazil, shaped like a finger, with the eastern end at the edge of the Brazil ‘nose’ meeting the Atlantic Ocean at the city of Recife. Dr. Vanessa van der Linden Mota, a pediatric neurologist working at Barao de Lucena Hospital (Recife), was puzzled by the frequency of cases and called her mother, Dr. Ana van der Linden, also a specialist, only to discover that she too was surprised. Dr. Gubio Soares, a virologist at the Federal University of Bahia (Salvador) was screening blood samples and coming to the conclusion that a mosquito was probably associated with spreading the virus. Dr. Celina M. Turchi, an infectious disease expert at the Oswaldo Cruz Foundation (Recife) alarmed by developments, set up a network of experts to brainstorm about the crisis, calling the group MERG (Microencephaly Epidemic Research Group). Within months, by August 2015, they had identified the probable culprit for the skyrocketing incidence of microcephaly: the Aedes aegypti mosquito. They alerted the health authorities in Brazil, who issued a health advisory. The team’s astute observations set the foundations for the current world-wide alarm.

Countries and Territories in the Americas with Active Zika Virus Transmission. Courtesy of the CDC.
Countries and Territories in the Americas with Active Zika Virus Transmission. Courtesy of the CDC.

Brazil has now mobilized 220,000 military personnel to battle the mosquitoes transporting the Zika virus. Before 2015, the Zika virus had not been recorded in the Western Hemisphere. As of now, the virus has been found in some 25 countries in the Western Hemisphere. On 15 January 2016, the U. S. Center for Disease Control and Prevention issued a travel alert directed at women of childbearing age warning them to avoid countries with Zika virus. That was the first time ever that a travel alert was aimed at a single class of people. On Monday, 1 February 2016, the World Health Organization declared a ‘public health emergency of international concern’. Dr. Scott Weaver, Director of the Institute for Human Infections and Immunity at the University of Texas Medical Branch in Galveston, Texas, suspects that it won’t be long until the mosquitoes are spreading the virus in places like Florida and Texas. On 28 January 2016, Dr. Anne Schuchat, of the CDC said “These types of mosquitoes are common in parts of the United States, particularly southern states. So it’s possible, even likely, that we will see limited Zika outbreaks in the United States. We do expect that we are at risk for local transmission.”

Why? Why has Zika virus all of a sudden spread throughout the Western Hemisphere? One likely scenario involves more international travel by asymptomatic people carrying the disease moving the virus around. Unlike the flu virus, Zika is not an airborne virus. The virus cannot spread without a carrier. And one probable reason for the spread of the disease is the spread of the carrier mosquito, Aedes aegypti, brought about by climate change. According to the UK Met Office, 2015 was the hottest year since records began in 1850. The Japan Meterological Agency and the United States National Oceanic and Atmospheric Administration concur: 2015 scorched the planet. Since 1950, the average temperature in Brazil has risen about 0.30 F per decade, which is a climb of about 1.40 F, on average, for the entire period. That might seem rather small, but if your body temperature goes from 98.60 F to 100.60 F, you know you are sick. The planet is sick. Since 1978, <a href=””>over 289,000 square miles of Amazon rainforest has been leveled</a>, an area a little bigger than Texas and South Carolina combined. Last year, Brazil mowed down some 2,000 square miles of forest, an area the size of Delaware. The double whammy of deforestation and global warming creates conditions conducive to the spread of mosquito breeding areas. Those insects thrive in hot, humid conditions, where they lay their eggs near the increasing amounts of stagnant water brought about by climate change. The Southern United States is becoming more hospitable to mosquitoes.

If you thought that “Fast and Furious” was limited to the movies, think again. A Porsch 918 Spyder goes from 0 to 60 mph in under 2.5 seconds. The number of cases of microcephaly in Brazil alone has gone from about 150 in a year to over 4,000 in six months. The number of cases of Zika virus has gone from 0 to over one million in the same period. Most people show no symptoms; some have rashes, fever, and pain; but, if pregnant, the virus can sneak into the fetus and disrupt brain development pathways, producing a small head with an underdeveloped neural network. The virus might also cause miscarriage.

Climate change did not produce the Zika virus. The virus has been around for awhile. But the Aedes aegypti mosquito can only survive in the right climatic conditions in the right environment, and its favored place to live is spreading due to climate change. Of the 4,000+ cases reported in Brazil, none emerged in the wealthy neighborhoods of Brasilia. The disease outbreaks are most common in the poor neighborhoods lacking proper sanitation and a reliable water supply, where residents store water in old toilets, cisterns, and other devices. And where water collects after rains and floods in areas lacking adequate drainage. Deforestation and climate change are not only related to global warming, but causes erratic weather patterns as the globe rotates and spins and the environment readjusts to changes in the landscape. Deluges occur in unexpected places at unusual times of the year. Mosquito breeding habitats are not confined to areas of deforestation, but crop up in villages, towns, and cities where stagnant water accumulates.

In the tropical regions of Africa and Southeast Asia, the dense forests are given crew cuts that yield the dual problem of releasing carbon into the atmosphere from dead trees, and reducing the natural carbon capture system of living trees. One type of disease-carrying Aedes aegypti mosquito has evolved a special ability to bite humans and survives quite well in human habitats. As the atmospheric conditions and physical environment around the globe change, we have new challenges to confront. One of those challenges is the emergence of infectious diseases. Conservation is a public health issue.

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