A type of algae found on the Brazilian coast could hold the key to a powerful new protection for women against HIV.
Tackling HIV in women is seen as a key priority
Brazilian researchers have developed a microbe-killing gel from the algae which they hope will be used to block HIV infection.
In preliminary lab tests they say it proved to be 95% efficient.
The team hopes the gel - one of a new generation of microbicides seen as key to preventing HIV infection in women - will be on the market in seven years.
The project is part of a worldwide research effort to develop microbicides - drug-delivery systems such as gels, rings, sponges or creams to prevent infection by HIV and other sexually transmitted diseases.
They are seen as a way for women to gain power by protecting themselves from HIV, particularly in impoverished nations where Aids is widespread, where rape is rampant, or, where conventional condoms are taboo, not reliably available or where men resist using them.
Leading HIV campaigners, including the US philanthropist Bill Gates, have said the key to stopping the Aids pandemic lies in giving women the power to protect themselves.
First-generation microbicides now being tested are expected to be available within four years and to be 50-60% effective.
However, preliminary tests of the Brazil gel suggest it could be substantially more effective.
Researcher Dr Luiz Castello Branco, an immunologist at the Oswaldo Cruz Institute in Rio de Janeiro, said the gel had produced impressive results during the first phase of testing over the last three years.
He said a second round of tests would start in February on mice and live cells from the cervix, with human studies starting next year.
He said: "We will certainly get to a final product with an efficiency above 50%.
"Right now we will test the product's safety and the ideal dose."
Roger Pebody, a treatment specialist at the HIV charity the Terrence Higgins Trust said: "Millions of women are exposed to HIV and cannot ask their partners or husbands to use condoms.
"Microbicides will give many more women the power to protect themselves.
"Many products are already being tested in human trials and could be available in as little as five years.
"Microbicides look set to be the best new prevention technology for vulnerable women in the hardest hit countries of Central and Southern Africa."