Science in the Triangle

The high-pitched hum of a mosquito increasingly carries the threat of disease in many parts of the world.

Mosquitoes can transmit West Nile, malaria, yellow fever, chikungunya and other viral diseases when they bite. The infections kill more than 1 million people every year.

Researchers in North Carolina’s Research Triangle are working on stemming the spread of mosquito-borne diseases, particularly dengue fever.

Globalization and poorly planned urbanization has increased the number of dengue infections more than four-fold since 1970s, putting two-fifths of the world population at risk, according to the World Health Organization. Along with the spread of the virus to about 60 countries, the risk of hemmorrhagic dengue fever has gone up. The severe form of the disease has become a leading cause of hospitalization and death among children in Southeast Asia.

Aravinda de Silva

“Dengue is a huge problem in the tropics,” said Aravinda de Silva, assistant professor of microbiology and epidemiology at the University of North Carolina at Chapel Hill.

U.S. travelers to Southeast Asia, Latin America and Africa can get infected - four cases of dengue fever were reported in North Carolina last summer - but local mosquitoes rarely pass on the virus outside of Hawaii and the Florida Keys.

De Silva spoke Tuesday at a forum on emerging infectious diseases at the N.C. Biotechnology Center. Other speakers were Katia Koelle, assistant professor of biology at Duke University, and Fred Gould, professor of agriculture at N.C. State University. The three talked about research under way to prevent dengue and possibly other mosquito-borne diseases.

Several vaccines are in the works. Glaxo SmithKline, a British drugmaker with U.S. headquarters in Research Triangle Park, is testing one in humans, so is French competitor Sanofi Pasteur and the National Institutes of Health. But vaccinating against dengue is tricky, because it potentially increases the risk of hemmorrhagic fever, de Silva said. “People have been very leery of a vaccine.”

Fred Gould

Another strategy is pest control through genetically engineered mosquitoes.

“If it works, we don’t need a vaccine,” Gould said.

It is a strategy that could also prevent other mosquito-borne diseases, he said, but genetic engineering can be controversial, whether it is done with corn, rice, fruit or insects.

The trouble with controlling dengue fever, particularly its severe form, is the virus and how the human body responds to it.

An estimated 50 million people are infected with the dengue virus every year, according to the WHO. Up to 90 percent develop immunity even though they don’t get sick. But the virus comes in four distinct strains and some of the strains have begun to show up in the same areas, causing secondary infections. The risk of developing hemmorrhagic dengue fever is 14 percent with a secondary infection compared to 2 percent the first time around, de Silva said.

The damage in the severe form of dengue fever is actually done by the person’s immune system responding to the infection, not the virus, he said. How that happens isn’t clear.

Katie Koelle

With a vaccine possibly becoming available within a few years, disease modelers like Koelle are trying to minimize secondary infection risks. They track dengue fever outbreaks and try to find patterns that could be useful in rolling out vaccines or in determining when it’s better to switch to pest control.

The WHO is working on a vaccination strategy, Koelle said.

Gould, however, is pursuing pest control through genetically engineering mosquitoes. The insects live long enough to lay eggs but die before they can transmit a disease. The offspring developing from the eggs then spread the genetic trait throughout the mosquito population.

Genetically engineering mosquitoes is similar to creating soybean seeds that are resistant to herbicides, Gould said. Researchers have been able to introduce genetic material that releases a toxin and kills the mosquito or that creates female mosquitoes that don’t bite because they can’t fly.

Pest control through genetic engineering has already been tested. Genetically engineered mosquitoes were recently released into the forest in Malaysia to see whether they help control dengue. (Read about the Malaysian experiment here.)

Gould will also talk about genetic engineering, pest control and mosquito-borne diseases at this month’s Triangle Global Health Consortium breakfast, 7:30 a.m. Feb. 24 at the biotech center.