The mosquitoes that changed history

Story highlights

  • British troops were beset with malaria during the American Revolution
  • Until the middle of the 20th Century, every war had more disease victims than combat victims

(CNN)In Spanish, mosquito translates to "little gnat," but its impact on history has been far from miniscule.

In just the most recent example, mosquitoes are spreading the Zika virus throughout South and Central Americas, causing an increased incidence of birth defects.
    However, the species of mosquito that carries the virus is endemic to Africa. So how did it travel across the ocean?
    "The slave trade," according to John McNeill, a history professor at Georgetown and author of the book, "Mosquito Empires."
    In fact, the species, Aedes Aegypti, is one of only three types of mosquito known to transmit disease among humans. According to the CDC there are 3,500 different species of mosquitoes.
    The other two species are Anopheles, which carries malaria, elephantiasis and encephalitis and Culex which carries encephalitis, elephantiasis and West Nile virus.
    "The Aedes Aegypti didn't exist in the Americas until the 16th century. That mosquito was brought from Africa to the Americas," said McNeill.
    Before Zika, Aedes Aegypti was best known to be a carrier of dengue and yellow fever. It's also known to carry encephalitis. By the 1940s, the idea of better living through chemistry had taken hold. In the U.S., efforts to limit dengue and yellow fever were successful because of targeted spraying campaigns. But as old concerns about the mosquitoes turned to new ones about effects of the pesticides, spraying efforts dropped, giving Aedes Aegypti and its mosquito brethren the chance to recolonize.
    It is not a stretch to say that in some ways mosquitoes -- and their propensity to spread disease -- influenced the course of world events, said McNeill.
    Until the mid-20th century, said McNeill, "every war had more disease victims than combat victims," in many cases spread by mosquitoes.
    During the American Revolution in the 1780s, the British chose a "southern strategy" and sent a large portion of their troops to the South. But this same area was rife with Anopheles mosquitoes and malaria. The British were fighting against the locally born and raised Continental Army, many of whom lived their entire lives in malaria zones, and were thus highly resistant, said McNeill.
    Once infected with malaria, a person who survives will build a resistance to the disease. The more times infected, the greater the resistance. Many of the British troops hadn't really been exposed to the disease and became infected, which incapacitated their army and required additional troops. Between June to November of 1780 "more than half of the British army was too sick to move," said McNeill.
    In World War II Americans gained an advantage over the Japanese because of malaria, according to Gordon Patterson, author of "The Mosquito Wars," and a history professor at the Florida Institute of Technology.
    The U.S. had moved 10,000 troops into active malaria zones in the South Pacific, but because the Americans had far greater resources to fight malaria relative to the Japanese, they were able to stay a much healthier fighting force, he said
    In fact, said Patterson, malaria was such a concern for America during World War II, the military created extended malaria programs to monitor and prevent the disease. One of the staging stations for these programs was in Atlanta. It eventually changed its name and became known as the Centers for Disease Control and Prevention.
    "This is nature's great drama of blood, sex and sugar," said Patterson. That's what mosquitoes are seeking when they suck your blood: sugar. And oddly, only the females do the biting. Actually they don't bite. They pierce the skin and suck.
    Mosquitoes and humans have a unique relationship, said Patterson. The mosquitoes that are most drawn to us, seem to have learned how to infiltrate our habitats, living in our buildings, and laying eggs in still water such as in gutters and cisterns.
    Our challenge to fight them is a public health issue and treatments such as air conditioning, filters on cisterns, effective water sourcing, and minimizing standing water are essential mosquito management tools. Even simple mosquito nets have been effective. And while these techniques have all contributed to the decline of disease overall, in some parts of the world, more effort is needed.
    Malaria is by far the most widely destructive mosquito-borne disease.
    According to the CDC, 40% of the world's population is at risk for dengue. The World Health Organization estimates that in 2012 there were more than 200 million cases of malaria and nearly 630,000 people, mostly children, died of the disease.
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