Scientists have developed a new weapon in the battle against mosquito-borne diseases, such as dengue fever and malaria, which afflict millions of people a year, killing many.
The weapon is the mosquitoes themselves — genetically modified.
Scientists engineered male mosquitoes (of a species that usually carries dengue fever) to contain a deadly gene that, when passed on to their offspring, kills them before they reach adulthood.
If enough of these mosquitoes are released into the wild and mate with females there, their progeny (or at least most of their progeny) won’t ever reach adulthood or mate — and that would spark a population collapse.
This technique improves on a method that has been around for decades: quelling pest populations by having sterile insects mate with wild ones. But the previous way of sterilizing mosquitoes (radiation) also harmed them, putting them at a disadvantage for mating with females when they were released back into the wild, meaning that they could not trigger a collapse of the overall mosquito population.
British biotechnology firm Oxitec engineered the new form of Aedes aegypti mosquitoes, the species that is the main transmitter of the dengue and yellow fever viruses.
They then released about 19,000 engineered male mosquitoes over four weeks in 2009 in a 25-acre area on Grand Cayman island. According to The New York Times,
Based on data from traps, the genetically engineered males accounted for 16 percent of the overall male population in the test zone, and the lethal gene was found in almost 10 percent of larvae. Those figures suggest the genetically engineered males were about half as successful in mating as wild ones, a rate sufficient to suppress the population.
Oxitec has already said a larger trial on Grand Cayman island in 2010 reduced the population of the targeted mosquito by 80 percent for three months. That work has not yet been published.
The researchers focused on male mosquitoes, because males do not bite humans, only females do. By releasing only the genetically engineered males, it prevents modified female mosquitoes from biting humans.
The experiment is causing controversy in the scientific community because Oxitec released the genetically modified organisms in secret a year ago and is only announcing they did so now. (Read this to see an argument for why this practice is dangerous, and read this to see the opposing side.)
Concerns about genetic engineering
For instance, some of the mosquitoes bred in the lab could develop resistance to the gene. If they are released into the wild without detection, it is unclear what would happen if they mated with the wild population.
Already, the Times reports, “3.5% of the insects in a lab test survived to adulthood despite presumably carrying the lethal gene.”
Oxitec is working on ways to prevent the release of mosquitoes who are resistant to the gene. The company says it, along with molecular biologist Anthony A. James of the University of California, Irvine, has developed a genetic modification that would prevent female mosquitoes from flying. This would make it easier to separate the females from the males before release into the wild, as well as keep the females from mating or biting people.
Oxitec is conducting an open-air trial with genetically engineered mosquitoes in Brazil. Also, the New York Times says,
Experts assembled by the World Health Organization are preparing guidelines on how field tests of genetically modified insects should be conducted. Proponents hope the field will not face the same opposition as biotechnology crops.
“You don’t eat insects,” said Dr. James of the Foundation for the National Institutes of Health. “This is being done for a good cause.”
photos: Top: Female Aedes aegypti mosquito (wild type) blood feeding. Middle: Adult genetically engineered male Aedes aegypti mosquitoes dusted with fluorescent powder. Bottom: Part of the rearing system for the genetically modified mosquitoes. Trays contain larvae; adults are housed in cages. (Derric Nimmo/Oxitec Ltd.)