A drug-resistant strain of the parasite that causes malaria has been identified by scientists in Rwanda.
The study, published in Nature, found the parasites were able to resist treatment by artemisinin - a frontline drug in the fight against the disease.
This is the first time scientists have observed the resistance to the drug artemisinin in Africa.
The researchers warns that this "would pose a major public health threat" in the continent.
Scientists from the Institut Pasteur, in collaboration with the National Malaria Control Program in Rwanda (Rwanda Biomedical Center), the World Health Organization (WHO), Cochin Hospital and Columbia University (New York, USA) analysed blood samples from patients in Rwanda.
They found one particular mutation of the parasite, resistant to artemisinin, in 19 of 257 - or 7.
4% - of patients at one of the health centres they monitored.
Evolution of parasites In the journal article the scientists warned that malaria parasites that developed a resistance to previous drugs are "suspected to have contributed to millions of additional malaria deaths in young African children in the 1980s".
When the first malaria drug, chloroquine, was developed, researchers thought that the disease would be eradicated within years.
But since the 1950s the parasites have evolved to develop resistance to successive drugs.
This is a deeply worrying and highly significant moment.
Today marks a setback in the fight against the malaria.
Resistance to artemisinin is not new as it has been in parts of South East Asia for more than a decade.
In some regions there, 80% of patients are now infected with malaria parasites that resist treatment.
But Africa has always been the biggest concern - it is where more than nine in 10 cases of the disease are.
It appears as though the resistance evolved in malaria parasites in Africa rather than spreading from South East Asia to the continent.
The result, however, is the same - malaria is getting harder to treat.
Malaria infection is now commonly treated with a combination of two drugs - artemisinin and piperaquine.
But then malaria parasites started developing a resistance to artemisinin as well - this was first recorded in 2008 in South East Asia.
At the time scientists they feared that resistance to artemisinin could also occur in Africa and have devastating consequences The research indicates that these fears may have been realised.
In 2018, African countries accounted for over 90% of the more than 400,000 deaths from malaria recorded.
Professor Lang Linfu, who was one of the scientists involved in its discovery of artemisinin, explains how he made the breakthrough.