Researchers from the University of the Free State (UFS), the National Health Laboratory Service and the University of Venda have 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, ‘South African brown locusts, Locustana pardalina, hosts fluconazole resistant, Candidozyma (Candida) auris (Clade III)’, highlights, for the first time, the presence of the pathogenic fungal yeast C. auris in the digestive tract of the locusts, and shows their potential in disseminating this emerging pathogen.

“Healthy humans are not at great risk for infection by this yeast and there is currently no proof that ingestion may be harmful to them.

“This is 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,” says UFS Department of Microbiology and Biochemistry Professor Carlien Pohl-Albertyn.

Pohl-Albertyn is also the South African Research Chairs Initiative National Research Foundation (NRF) research chair in Pathogenic Yeasts.

The researchers isolated three C. auris strains from three different adult locusts, two of which also harboured strains of another potentially pathogenic yeast Candida orthopsilosis.

“The fact that we were able to isolate C. auris from 15% of the sampled locusts using non-elective 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,” she notes.

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.

Isolation from the hindgut confirms that C. auris can survive the digestive processes in the midgut and is likely to be released back into the environment via faeces.

Further, 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 is a characteristic of this yeast species, and thus not surprising, and most of the emerging pathogenic yeasts show this intrinsic resistance. This highlights the urgent need to discover and develop new antifungal drugs, she says.

There are treatment options available using other antifungal drugs, but C. auris can become resistant to all the currently available antifungal drugs, Pohl-Albertyn says.

“The fact that locusts are a food source for other animals, such as birds, could lead to eventual distribution of the yeast to people. In some countries, wild locusts are a food source for humans and more direct transmission may be possible,” she adds.

The study tries to answer questions regarding the natural hosts of this emerging pathogen and how it may facilitate the spread of the pathogen to the rest of the environment. The study is one part of the puzzle regarding how new pathogens may 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.

“It is well known as a hospital-acquired pathogen, but it is not known where in the environment it occurs naturally, and which environmental factors may have shaped its evolution and ability to cause human infections.

“This has implications for the prevention of the spread of this specific yeast species, as well as our preparedness for new pathogenic yeasts that may be emerging from the environment,” says Pohl-Albertyn.

The research started in April 2022 when 20 gregarious, or 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, the researchers say.