Marqui Ducarme is aided by his wife after catching chikungunya at his home in Port-au-Prince, May 23. The virus swept through Haiti this spring, infecting more than 40,000 people. Marie Arago/Reuters/Landov hide caption

itoggle caption Marie Arago/Reuters/Landov

The World Cup will come to the Arena de Sao Paola, shown here when it was under construction last fall. Brazil is also making a big push to control the local mosquitoes that can spread dengue fever. Friedemann Vogel/Getty Images hide caption

itoggle caption Friedemann Vogel/Getty Images

Red blood cells infected with the Plasmodium falciparum parasite. Plasmodium is the parasite that triggers malaria in people. Gary D. Gaugler/Science Source hide caption

itoggle caption Gary D. Gaugler/Science Source

The mosquitoes that feed on people are attracted to over 300 gases and other compounds emitted by human skin. CDC Public Health Image Library hide caption

itoggle caption CDC Public Health Image Library

If you catch dengue fever in the Western Hemisphere, it most likely came from the Aedes aegypti mosquito. Muhammad Mahdi Karim /Wikimedia.org hide caption

itoggle caption Muhammad Mahdi Karim /Wikimedia.org

Chiara Andolina, a malaria researcher in Thailand, feeds her mosquito colony by letting the insects bite her right arm. These mosquitoes are picky and will dine only on live human blood. Ben de la Cruz/NPR hide caption

itoggle caption Ben de la Cruz/NPR