A discovery could lead to drugs to cure 'forgotten' tropical diseases that kill thousands of people each year.
Leishmaniasis is common in parts of Africa
A University of Dundee team discovered a drug target common to three parasitic diseases rife in the developing world.
The Scottish researchers believe this will enable new drugs to be developed to overcome the problem of resistance to current, old-fashioned drugs.
Tropical diseases are 'unprofitable' and thus neglected by drug companies, scientists and charities said.
Professor Alan Fairlamb and his team looked at parasites causing three different diseases - sleeping sickness, Chagas disease and leishmaniasis.
He found the parasites all had one thing in common - they possessed a molecule called trypanothione.
It is this molecule that current drugs to treat Chagas disease and sleeping sickness target.
It was suspected that the drugs to treat leishmaniasis, called antimony drugs, acted on the same target.
Now this has been proven, said Professor Fairlamb.
The problem with existing drugs is that the parasites have found ways to escape treatment.
Knowledge of how treatment resistance occurs should help scientists design more effective drugs, the researchers hope.
They have worked out that trypanothione is vital for parasite survival and now know several enzymes that new drugs will need to target.
Professor Fairlamb said: "Many cases of leishmaniasis in India are now proving resistant to the traditional antimony drugs so new modern drugs are needed soon.
The parasite diseases
Sleeping sickness is spread by the tsetse fly
Chagas disease is spread by bites from beetle-like bugs
Leishmaniasis is spread through bites from sand flies.
"We now have several target enzymes that we are putting into drug screening programmes to try to find better drug treatments."
He hopes such drugs could be available in the next five to 10 years.
Simon Croft, research and development director at the Drugs for Neglected Diseases Initiative (DNDI), which is part of Médecins Sans Frontières, said: "It's interesting news.
"This is an important drug target. DNDI and other organisations are funding people to look for new drugs that will go for this target."
Professor Fairlamb and a spokesman from Médecins Sans Frontières both said pharmaceutical companies did not provide enough funding for these diseases because most of the people affected were from the developing world which was not a profitable market for sales.
Professor Fairlamb said: "If we can come up with a validated drug target and couple that with a lead compound, that would limit the financial risk for drug companies."