Collectively, these so-called “neglected tropical diseases” affect tens of millions of people and claim more than 50,000 lives each year.
Chagas, sleeping sickness and leishmaniasis are caused by infection from parasites sharing a similar genetic profile.
The scientists identified an enzyme common to these pathogens, and then developed a chemical that targets the enzyme and prevents it from functioning.
They reported their results in the peer-reviewed journal Nature.
“It’s a breakthrough in our understanding of the parasites that cause the three diseases, potentially allowing them to be cured,” said Jeremy Mottram, a professor at the Centre for Immunology and Infection at the University of York in England, and co-author of the study.
Before proceeding with human trials, researchers need to test the compounds for toxicity, he said in a statement.
In experiments, mice tolerated the drug well.
To find the potential silver bullet, scientists tested three million compounds — part of a chemical library held by drug giant Novartis — on live parasites.
Using synthetic chemistry, they then tweaked the most promising molecules to find the one most effective against all three diseases.
The most deadly of the trio — trypanosomiasis, commonly known as sleeping sickness — is fatal if left untreated. Transmitted by the tsetse fly, it is widespread in sub-Saharan Africa.
Early symptoms include headache, anaemia and joint pains, while later infection produces severe neurological and hormonal problems.
As the parasite invades the central nervous system, mental deterioration sets in, leading to coma and death.
Finding a drug that can target the disease in the brain is difficult, but the researchers made a breakthrough in experiments with mice.
The first step was to infect the rodents with parasites genetically modified to emit light.
“We were able to detect the parasite in the brain using an imaging system,” explained co-author Elmarie Myburgh, also of the University of York.
“We then tested the chemical developed by Novartis using our imaging method, which showed that it can get into the brain and kill the parasite.”
The compound proved effective against the other two diseases as well.
There are about two million cases of leishmaniasis every year in nearly 90 countries worldwide.
The most severe form — known as visceral leishmaniasis — attacks internal organs, while the more common variant causes face ulcers and disfiguring scars.
More than 120 million people are at risk from Chagas disease, with 300,000 new cases every year.
The disease, caused by the parasite Trypanosoma cruzi, results in high fever and swollen glands to start, especially in young children.
Symptoms can subside, often for years. But during that time the parasite is progressively infecting most of the body’s organs. It can cause fatal damage to the heart and digestive tract.
Although treatments for all three diseases exist, they are expensive and cause side effects, as well as not working very well.
By contrast, when the new compound was tested on mice, it did not appear to disturb the normal functioning of the animals’ cells.
The three illness are all classified by the World Health Organization as “neglected tropical diseases” that mainly affect people living in poverty, without adequate sanitation and in close contact with animals and livestock.