Yeast strain in brown locusts can cause severe infections in seriously ill people: study

A new study has confirmed for the first time that common brown locusts are carriers of pathogenic yeasts that can cause severe infections in humans, especially in people with compromised immune systems or who are seriously ill. 

The study was conducted by researchers from the University of the Free State (UFS), the National Health Laboratory Service and the University of Venda.

The study highlights for the first time the presence of the pathogen (disease-producing) fungal yeast C auris in the digestive tract of the locusts. The study also shows the brown locusts’ potential in disseminating this emerging pathogen.

The research started in April 2022, when 20 swarming adult locusts were collected during a large locust outbreak which occurred from September 2021 to May 2022 in the semi-arid Eastern Karoo region in the Eastern Cape. The study is still under peer review. 

Prof Carlien Pohl-Albertyn, National Research Foundation  SARChI research chair in pathogenic yeasts, said three C auris strains were isolated from three different adult locusts, two of which also harboured strains of another potentially pathogenic yeast, Candida orthopsilosis.

“That we were able to isolate C auris from 15% of the sampled locusts, using non-selective media and a non-restrictive temperature of 30°C, may indicate that C auris is abundant in the locusts and that specific selective isolation is not mandatory,” Pohl-Albertyn said.

 She said C auris was isolated from the fore- and hindgut of the locusts.

“Isolation from the foregut, which is dedicated to food intake and storage, filtering and partial digestion, indicates that C auris was probably obtained by the locusts via feeding activities.” 

She said isolation from the hindgut confirmed that C auris could survive the digestive processes in the midgut and was likely to be released back into the environment via faeces. 

Researchers said one of the C auris strains was studied in more detail. This strain was not resistant to disinfectants but showed decreased susceptibility to the common antifungal drug Fluconazole.

This was a characteristic of this yeast species and thus not surprising. Most of the emerging pathogenic yeasts showed this intrinsic resistance. Researchers said this highlighted the need to discover and develop new antifungal drugs. 

Pohl-Albertyn, who is also a professor of microbiology in the UFS department of microbiology and biochemistry, said healthy humans were not at great risk for infection by this yeast and there was no proof that ingestion might be harmful to them.

“This is unfortunately not the case for people with compromised immune systems or who are seriously ill. However, few susceptible people come into direct contact with the locusts in South Africa.” 

She said there were treatment options available, using other antifungal drugs, but C auris could become resistant to all the now-available antifungal drugs. 

She said the fact that locusts were a food source for other animals, such as birds, could lead to eventual distribution of the yeast to people.

“In other countries, wild locusts are a food source for humans and there more direct transmission may be possible,” Pohl-Albertyn said. 

She said the study tried to answer questions regarding the natural hosts of this emerging pathogen and how it might facilitate the spread of the pathogen to the rest of the environment. The study was one part of the puzzle regarding how new pathogens might emerge from the environment and spread to people. 

“One of the questions in the field of pathogenic yeasts is how C auris was able to emerge as a pathogen in several different countries in a relatively short period.”

She said C auris was well known as a hospital-acquired pathogen, but it was not known where in the environment it occurred naturally, and which environmental factors might have shaped its evolution and ability to cause human infections.

Pohl-Albertyn said this had implications for the prevention of the spread of this specific yeast species, as well as preparedness for new pathogenic yeasts that might be emerging from the environment. 

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