** ADVANCE FOR MONDAY, AUG. 22 ** Schistosoma mansoni worms, the cause of schistosomiasis, a microscopic worm that plagues more than 200 million across the globe, are seen through a microscope at the lab of University of Georgia professor Dan Colley on the school's campus in Athens, Ga., July 27, 2005. Colley's study of the deadly parasite just won him the Brazilian Presidential Medal for Scientific Merit, the country's highest scholarly honor. (AP Photo/Ric Feld)

ive years after the launch of an international effort to combat the burden of tropical diseases, global health leaders say enormous progress has been made toward freeing some of the planet’s poorest people from some of nature’s most gruesome and debilitating threats.
The effort to ease the burden of neglected tropical diseases has been led by the World Health Organization and a host of other institutions and nonprofits, notably the Bill and Melinda Gates Foundation. They have worked with pharmaceutical companies to arrange large-scale drug donations — 1.5 billion treatment courses in 2015 alone — and cultivated political support for action in affected countries.
On Tuesday, backers of the initiative are gathering in Geneva to mark five years since the signing of the London Declaration on Neglected Tropical Diseases, a commitment to try to rid the world of scourges like Guinea worm — in which people become infected with worms that bore …