April 22 (Bloomberg) -- Scientists seeking a way to prevent transmission of the deadly dengue virus, which affects two- fifths of the world’s population, have discovered which genes allow the disease to spread.

Tools for studying mosquito genetics haven’t been developed, so researchers led by Mariano Garcia-Blanco at Duke University in Durham, North Carolina, used cells from the gut of the related fruit fly. The scientists determined there were 116 genes that allow dengue to grow, of which 42 correspond to similar DNA in humans and at least one to mosquitoes, according to the study published today in the journal Nature.

There’s no cure for the disease, and no vaccine. The latest finding may lead to new antiviral drugs, said Priscilla Yang, a study author and microbiologist at Harvard Medical School in Boston. The virus spreads through humans and mosquitoes only, and understanding its life cycle from the genetic level up may allow scientists to begin researching ways to block the pathways it uses in its hosts, Yang said.

“This is a starting point,” Yang said in a telephone interview today. “When we talk about antivirals, we don’t understand enough about what dengue does to manufacture them. This experiment defines what resources the virus needs.”

About 2.5 billion people live in areas prone to dengue, a family of four mosquito-borne viruses the Geneva-based World Health Organization says cause about 50 million infections yearly. Dengue causes sudden onset of fever, severe headache and muscle and joint ache lasting a week to 10 days. It can also trigger a drop in white blood cells and platelets, leading to excessive bleeding and death.

Before 1970, nine countries had experienced epidemics of dengue hemorrhagic fever, and the number had more than quadrupled by 1995, WHO said.

Garcia-Blanco and his team infected fruit fly cells with dengue type-2, then switched off one gene at a time to find the host factors that, when silenced, prevented the virus from multiplying.

Dengue is mostly transmitted by Aedes aegypti, a mosquito that is infesting more areas because of global trade and bans on pesticides such at DDT.

To contact the reporter on this story: Simeon Bennett in Singapore at sbennett9@bloomberg.net

Last Updated: April 22, 2009 13:00 EDT