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