Old drug is new weapon against tsetse flies

A drug that combats a rare human genetic disease is lethal to blood-sucking insects...

Tsetse flies are blood-sucking insects found in parts of Africa south of the Sahara Desert. Like some other insects that feed on blood, they can spread disease. In this case, they transmit African trypanosomiasis, known more colloquially as sleeping sickness. Infected tsetse flies introduce the trypanosome parasite that causes the disease when they feed.

Sleeping sickness affects 3500 people per year, many of them lethally. There is no vaccine, and drugs to treat the infection can be expensive and difficult to obtain. Insecticides can control tsetse fly numbers to some extent, but they also have negative effects on other insects including essential pollinators. And despite decades of efforts to control it, the disease is still prevalent. 

Now there is fresh hope. In a research paper published this week in PLOS Biology, a global collaboration of researchers have shown how a drug called nitisinone, which is already used in humans to treat a rare genetic disease, kills these insects when they feed on blood that contains the drug.

Study author Álvaro Acosta-Serrano said, "flies that are exposed to that drug, they quickly die."

Tsetse flies fed with drug-laced blood in the lab died within 18 hours. This also happened even if the insects just touched the drug. According to the researchers, the drugged insects develop a killer case of indigestion.

This is because, when they feed, tsetse flies can routinely consume more than twice their own body weight in blood. This liquid lunch is rich in proteins, which are toxic to the insects if they accumulate. Usually, they are broken down and detoxified, but the drug stops this happening, so the flies die.

Only a very small amount of the drug is lethal for the flies, the team have found. And because is has very few side effects in humans, and is non-toxic to pollinating insects, like bees, it could be a useful lead for the control of tsetse flies in sleeping sickness endemic areas. Admittedly it is expensive at the moment, but other, cheaper drugs that work in a similar way could be developed to work along the same lines.

"I think there is great potential to exploit these compounds depending on the biology and depending on the kind of insect that we try to control," Acosta-Serrano says.