Of all the disease-spreading insects in the world, the mosquito poses the greatest menace, according to the World Health Organization (WHO). As if to underscore that threat, two mosquito-borne viral diseases have begun to spread well beyond their points of origin. One is dengue fever, a potentially deadly illness, and the other is chikungunya, a debilitating and painful disease from which most people can recover. There are no vaccines to prevent these diseases. But researchers are working hard to develop vaccines against dengue fever and chikungunya, and to control the mosquitoes that spread them.
Scientists have identified at least 3,000 different species of mosquitoes throughout the world. The Asian tiger mosquito is one that bites during the day.
The tiger mosquito's bite is more than annoying. It's responsible for infecting 20 million people a year with dengue fever, a flu-like illness that can result in hemorrhagic fever, shock syndrome, and even death.
"It's almost completely spread throughout the tropics and subtropics throughout the world," said Weaver.
Scott Weaver at the University of Texas Medical Branch confirms what other scientists are seeing, mosquitoes that can transmit dengue fever have spread though India, Southeast Asia and Latin America and are finding their way around the world. There were more than 12 confirmed cases this year in Florida, in the southeastern United States.
The tiger mosquito can also spread chikungunya, a debilitating disease that causes extreme joint pain and fever. The illness is spread as well by an African mosquito, which is also expanding its range. Professor Laura Harrington is an insect specialist at Cornell University. She says it's not just the mosquitoes' range that's changing:
"We're also seeing changes, particularly with the viruses; we're seeing changes in their genetic material which often can lead to increased virulence," Harrington noted.
On top of that, mosquitoes can arrive in new destinations aboard planes and in cars.
"It's a virus that has the ability to travel on airplanes and in infected people very readily," Weaver added.
Weaver is working on a vaccine for chikungunya that has successfully protected lab mice from getting the virus. At Cornell, Harrington is working to make the male mosquito infertile.
"The idea is that these modified males that don't take a blood meal could be released, mate with the wild females, the females wouldn't reproduce, they wouldn't take a blood meal, and the population would be eliminated or reduced," Harrington explained.
Both scientists are concerned that if a way to control the spread of chikungunya and dengue fever is not found soon, both diseases will become established in the United States. Harrington says that techniques that prove successful against these illnesses might also be used to break the cycle of other mosquito-borne diseases, including malaria.