Sleeping sickness: An experimental drug cleared the parasite from the body in a clinical trial


In a small trial, an experimental medicine was 100 per cent effective at ridding the parasite that causes sleeping sickness from the bodies of people with an early to intermediate infection


29 November 2022

A species of the Trypanosoma brucei parasite, which can cause sleeping sickness, in blood

A Trypanosoma brucei parasite, which can cause sleeping sickness, in blood

Kateryna Kon/Shutterstock

A single pill may be 100 per cent effective at treating early-to-intermediate stage sleeping sickness. In a small trial, people with this stage of sleeping sickness showed no signs of having the parasite 18 months after receiving the experimental treatment.

The drug was even 95 per cent effective at clearing the parasite when it may have already spread to the brain, a sign of an advanced infection.

Sleeping sickness, also known as African trypanosomiasis, is a parasitic infection that is endemic to West and central Africa. Fifty-five million people were at risk between 2016 and 2020, of whom 3 million were at moderate or higher risk.

The condition, caused by Trypanosoma brucei, typically spreads via tsetse flies, which pick up the parasite when consuming the blood of an infected mammal, such as dogs, livestock or humans. Early symptoms include fever, weakness and itching. Although often mild initially, the infection can quickly become severe and even fatal.

The main way to treat the infection is via a drug called fexinidazole. Although up to 91 per cent effective at removing the parasite, fexinidazole must be taken orally once a day for 10 days with food. It also has several common side effects, including vomiting. According to the European Medicines Agency, fexinidazole must be taken under medical supervision.

To test the potential of a one-off drug called acoziborole, Anthoine Tarral at the Center for Neglected Diseases in Switzerland and his colleagues analysed 208 people over the age of 15 in the Democratic Republic of the Congo and Guinea. The participants were diagnosed with sleeping sickness between October 2016 and March 2019.

More than three-quarters of the participants were given acoziborole while in a late stage of the infection, defined as the sleeping sickness parasite being in their cerebrospinal fluid, suggesting that the infection may have reached their brain.

The remaining participants were treated during an early to intermediate stage of the infection, defined as the parasite being in other bodily fluids, but not cerebrospinal fluid. All participants were followed for 18 months after treatment.

Acoziborole wasn’t compared against fexinidazole due to there being relatively few people in the study areas who had been diagnosed with sleeping sickness, says Tarral. The sample size in each treatment group would therefore have been too small to give a meaningful comparison, he says.

Among the participants with late-stage sleeping sickness, acoziborole had a 95 per cent success rate, defined as no parasite being found in various bodily fluids at 18 months post-treatment. This rose to 100 per cent among those with an early to intermediate infection. The researchers didn’t measure at what point in the 18 month follow-up period the parasite was cleared from the participants’ bodies.

If not treated properly, the parasite can linger and cross the blood-brain barrier, invading the central nervous system and causing severe symptoms.

According to Tarral, acoziborole could help the World Health Organization (WHO) achieve its target to eliminate the transmission of a common form of sleeping sickness worldwide by 2030.

“This drug can change the world of this disease,” he says. Acoziborole could be available in two years, says Tarral.

Acoziborole caused just a few mild-to-moderate side effects. Thirteen of the participants reported vomiting. It is unclear whether this was a result of the drug, the infection or an unrelated factor.

“The findings show acoziborole to be a safe, effective, oral therapy for the treatment of human African trypanosomiasis,” says David Horn at the University of Dundee, UK.

“The target set by the WHO is to interrupt disease transmission by 2030 and the challenges here must not be under-estimated, but the improvements that acoziborole offers over current alternative therapies could prove pivotal in helping to reach this goal.”

Journal reference: The Lancet Infectious Diseases, DOI:

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