Altering Bugs Effective Way To Help Eradicate Disease (5/24/2007)

Releasing genetically modified male mosquitoes could eliminate the danger of dengue fever and other mosquito-borne diseases within a year in communities of up to a million people, according to a research paper released this week.

Health professionals have tried different techniques to control disease-bearing mosquitoes, including a strategy called Released Insect with a Dominant Lethal, or RIDL, which uses genetically modified male mosquitoes to produce offspring that die shortly before or after birth.

"The RIDL approach is an alternative that is also environmentally benign," said Lawrence M. Wein, the Paul E. Holden Professor of Management Science at the Stanford Graduate School of Business, one of the authors of a paper released May 14 by Proceedings of the National Academy of Sciences.

RIDL mosquitoes have proven more effective than insects that are irradiated to make them sterile, he added, because the genetically modified male insects are more physically fit to compete with the mosquitoes in the wild than those that have been subjected to radiation.

However, scientists have had difficulty trying to figure out the effectiveness of such campaigns and to determine the right proportion of altered insects necessary to have an impact on infected mosquito populations.

Wein and his co-researchers developed a mathematical model that predicts the effectiveness of RIDL eradication campaigns.

Their paper, "Analyzing the Control of Mosquito-Borne Diseases by a Dominant Lethal Genetic System," was authored by Michael P. Atkinson and Zheng Su of Stanford's Institute for Computational and Mathematical Engineering, Nina Alphey and Luke Alphey of the University of Oxford, Paul G. Coleman of the London School of Hygiene and Tropical Medicine and Wein.

Mosquito-borne diseases, such as dengue fever, are a major health problem in many countries, especially in the developing world. There is no licensed vaccine for dengue, which affects up to 100 million people each year. Between 250,000 and 500,000 potentially fatal cases are reported annually.

One of the known dengue-causing types of mosquitoes is endemic in the southeastern United States. The recent spread of the West Nile virus has raised concerns that the United States may be vulnerable to other serious outbreaks of mosquito-borne diseases.

Health professionals have used different methods to battle dengue and other similar diseases, such as launching sanitary campaigns in affected communities and trying to eradicate mosquito populations in their natural habitat.

Recently, scientists have tried different approaches aimed at suppressing the infected insects' ability to reproduce. One technique, called Sterile Insect Technique, or SIT, introduces male mosquitoes that have been irradiated and rendered sterile in order to mate with infected female insects.

The RIDL method uses genetically modified mosquitoes to cause the offspring of female insects to "die either before or after the larval stage," the study said.

Wein said that based on their research into the RIDL method, "Eradication of the disease might be feasible within about one year for affected populations in the order of 100,000 to a million."

"This was a mathematical study to get an order of magnitude," he added.

"From a practical point of view, it is important to understand how many … mosquitoes are required for eradication and how long it takes to eradicate the virus," write the authors. "Our model should suffice for an order-of-magnitude assessment of the effectiveness and practicality of the RIDL strategy."

However, Wein said the strategy also entails serious challenges.

"The real drawback is the logistical consideration," he said. "Once you release the mosquitoes, they only travel half a mile. So if you try to eradicate the disease in a rural area where there are distances between neighbors, you pretty much have to hand-deliver the insects."

Wein is known for his work exploring homeland security issues related to potential anthrax attacks and the effectiveness of the two-finger fingerprinting system used on the U.S. border. He has also testified before a variety of government agencies considering policies on public health, epidemics and bioterrorism.

Note: This story has been adapted from a news release issued by Stanford University

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