29 June 2007

Genetic Research on Insects Could Lead to Disease Prevention

Introduction in disease-prone areas a decade or more away

 

Genetically modified mosquitos introduced into the wild could reduce the spread of malaria in humans. (© AP Images)

By Kathryn McConnell
Staff Writer

Washington -- U.S. scientists have created a genetically modified malaria-resistant mosquito that one day could be introduced in natural settings, outbreed ordinary “wild-type” mosquitoes and reduce the spread of malaria in humans.

But potential human health benefits from this discovery, reported in the March 2007 journal Proceedings of the National Academy of Sciences, still might be several years away, perhaps 10 years to 20 years, said Jason Rasgon of Johns Hopkins Malaria Research Institute in Maryland. The institute is one of the world’s leading malaria research centers.

Scientists also are studying how genetically modified insects might be able to hinder the transmission to humans of such deadly or debilitating diseases as dengue fever, found globally; sleeping sickness in Africa; and Chagas disease (American trypanosomiasis), an illness transmitted by parasites that is prevalent in Latin America.

Yet limited public funding for biomedical science research is making it “more difficult” for scientists to make rapid strides in promising areas for research on genetically modified organisms, Rasgon told USINFO.

Such private funding sources as the Bill and Melinda Gates Foundation, which has contributed millions of dollars to international health care efforts, supplement but “are not replacements for federally sponsored biomedical research” in terms of the level of funding needed and the range of research required, he said.

In the Johns Hopkins study, researchers put into a cage a group of mosquitoes born from eggs scientists had inoculated with a gene that halts the transfer of a malaria parasite from mosquitoes to rodents.

They then placed in the cage an equal number of nontransgenic mosquitoes and allowed them feed together on a mouse infected with malaria. The modified mosquitoes, distinguishable from the others because their altered gene made their eyes fluorescent green, proved to be more resistant to the malaria parasite and also laid more eggs. That increased resistance to the parasite means the transgenic mosquitoes are less likely than the naturally occurring mosquitoes to transmit malaria to humans.

After nine generations of approximately two-week life cycles, 70 percent of the genetically modified insects survived compared to 50 percent of the nontransgenic insects.

These results indicate that the genetically modified mosquitoes would reproduce more successfully than their nonmodified counterparts and each generation of genetically modified offspring would be consecutively stronger, more numerous and more capable of reversing the rate of malaria infection in a population, scientists say.

Scientists do yet know how well the transgenic and wild mosquitoes might mix in field conditions. And, as with all transgenic insect research conducted in the United States, there are environmental, legal and social concerns researchers must address with the national government and with local communities that are the proposed sites of field tests.

The Johns Hopkins finding holds the promise that one day researchers will find a way to make transgenic mosquitoes that are unable to transmit the Plasmodium falciparum parasite to humans, reducing the need for human vaccines (to which the parasite carried by mosquitoes is becoming increasingly resistant), or for mosquito-control strategies such as pesticide use.

Most of the research conducted thus far on ways to reduce the impact of malaria on humans has focused on developing drugs that boost human immunity or counteract the malaria parasite once it is in a person's bloodstream.

The World Health Organization estimates that malaria kills more than 1 million people each year.

In related research, Serap Aksoy of the Yale School of Public Health told USINFO she is investigating ways to genetically modify tsetse flies to block their ability to transmit the parasite that causes sleeping sickness in humans, which is estimated to affect 50,000-70,000 people, mostly in sub-Saharan Africa.

Ravi Durvasula, also of the Yale School of Public Health, said he is working on engineering bacteria to make what is known as the "kissing bug" inhospitable to the parasite that transmits Chagas disease.

Thomas Scott of the Department of Entomology at the University of California, Davis, said he is studying ways to make male mosquitoes sterile, thus reducing the mosquito populations and the chances they will spread dengue fever, which infects an estimated 50 million people each year.