Scientists have found a kind of drug that can kill the parasites that cause three tropical diseases that sicken millions of people in Africa, Asia and Latin America - Chagas disease, leishmaniasis and sleeping sickness.

The medical journal Nature, reports that scientists at the Novartis Research Foundation found a chemical that can cure all three diseases in mice, and what is more it does not hurt normal human cells in tests, so far. This will be a good starting point for making new drugs to replace the old treatments that cost a lot, often don't work very well, and can have side effects.

Chagas, leishmaniasis and sleeping sickness kill more than 50,000 people every year, but possibly because they mostly happen in very poor parts of the world, not much money has been spent on research into new drugs.

The three diseases show up differently, but they are all caused by very similar parasites called kinteoplastids. Hoping to find a "weak spot" in the parasites, the scientists tested around 3 million chemicals on them. They found one that worked, then they refined it to make it stronger and then it was tested on mice.

The fact that the drug seems to have no bad effects in mice shows that it might have fewer side-effects than the drugs used now, but the researchers say this will need to be tested in human studies.