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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 research released this week.
Health professionals have tried different techniques to control
disease-bearing mosquitoes, including a process called Released Insect with
a Dominant Lethal, or RIDL, that uses genetically-modified male mosquitoes
who 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
published today by Proceedings of the National Academy of Sciences of the
United States of America.

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-born 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-born 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 Sterilize
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 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's 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 affecting public
health, epidemics, and bioterrorism.

[www.gsb.stanford.edu]