Despite their innocuous resemblance to the common house fly, tsetse flies are the source of a serious public health concern in the Sub-saharan African countries where they most commonly occur. The blood sucking insect is the transmitting vector of trypanosomes, parasites which cause sleeping sickness in humans and animals. 

When left unchecked, human sleeping sickness is deadly, especially to those living in rural communities without effective healthcare access. High mortality outbreaks of animal sleeping sickness among livestock populations, especially cattle, are known to cause agricultural devastation and large economic loss. 

In order to combat these devastating outbreaks, communities deploy traps designed to reduce the population of tsetse flies. To make these traps most effective, they are often imbued with odorous chemical compounds from the 3-alkylphenol family which attract the insects. However, these compounds are usually derived through costly and elaborate chemical processes, making them inaccessible to the areas which need them most. 

A new paper from researchers at Goethe University in Germany details the development of an inexpensive “yeast brew” which produces these chemical compounds that attract the tsetse into traps and can be easily produced locally in the Sub-saharan rural communities most affected by sleeping sickness.

The team set out to modify a strain of the popularly used baker’s yeast Saccharomyces cerevisiae. The microbe is possibly best known as being the key ingredient in bread, beer, and wine for hundreds of years. In addition to being common, there are strains of S. cerevisiae which are capable of fermenting agricultural waste, a possibility which would make the process of developing the attractant incredibly cost-effective. 

The researchers introduced the yeast to a new metabolic pathway so it would produce high concentrations of the chemical compounds 3-ethylphenol and 3-propylphenol (3-EP and 3-PP), members of the 3-alkylphenol family which show the greatest potential as tsetse fly attractants. 

Researchers from Addis Ababa University in Ethiopia previously found that cow urine, which is high in naturally occurring concentrations of 3-EP and 3-PP, is also promising as a sustainable and cost-effective trap attractant. In 2012, researchers from the University of Edinburgh’s College of Medicine and Veterinary Medicine suggested applying insecticide to cattle should be the priority method to control tsetse to animal infection. 

Because there are currently no vaccines or preventative drugs for combating the disease, tsetse fly traps remain a crucial factor in mitigating sleeping sickness infections.  

The disease progresses slowly, often with minimal to no symptoms in the first few months of infection. The average duration of symptom progression in the West African strain of sleeping sickness takes place over the course of three years. Muscle aches, swollen lymph nodes, fever, and extreme fatigue are among the most common symptoms, and immediate intervention is necessary and often includes hospitalization. Recurring check ups may take place over the course of years and even if a person has the disease once, re-infection is possible. 

In recent years, there has been significant progress in reducing the number of sleeping sickness infections in humans. The World Health Organization targeted the elimination of human sleeping sickness as a priority issue in 2012. In 2018, there were 977 reported cases down from 2,164 in 2016.

Now, the researchers are working on getting the yeast to local populations to be tested. They’re also looking into developing the yeast to produce other alkylphenols with potential applications in cleaning products and lubricating oil additives.