Genetic hitchhikers make Aspergillus infections even harder to treat

Lisa Lock

Scientific Editor

Robert Egan

Senior Editor

Resistance to antifungal medicines in the pathogenic fungus Aspergillus fumigatus is proving more persistent than previously thought. Research by Wageningen University & Research (WUR), published in Current Biology, shows that fungicides used in agriculture, even those with a different mode of action from these medicines, can help maintain this resistance. This is because different resistance genes "hitchhike" together.

Under the microscope, Aspergillus fumigatus is a remarkably beautiful fungus. It has a delicate stalk topped by a swollen head, with clusters of tiny spheres on its surface. These spheres are microscopic spores that spread through the air in vast numbers. The fungus naturally grows mainly in plant waste and compost heaps, where it helps break down plant material.

But people with weakened immune systems—for example, those undergoing cancer treatment or who have undergone an organ transplant—can become seriously ill if they inhale the spores. "Once someone develops a serious infection caused by this fungus, the outcome is unfortunately often fatal," explains Eveline Snelders, a medical mycology researcher at Wageningen University & Research.

Since the beginning of this century, treatment with antifungal medicines such as azoles has increasingly failed in patients infected with the fungus. The fungus has developed resistance. About 10% of Aspergillus infections are now caused by a resistant strain. Snelders and her colleagues have discovered that the problem is even more complex than they previously thought, due to combinations of resistance mechanisms in Aspergillus.

A revelation

The problem is growing on two fronts: more fungi are becoming resistant, while the number of vulnerable patients is increasing. Early in her research, Snelders discovered that the medical azoles used to treat Aspergillus infections are similar to the azoles used in agriculture to control other fungal species that threaten crops.

"As medical mycologists, we had no idea that such closely related substances were being used in such enormous quantities. It turned out to be tons, under slightly different names and with slightly different chemical structures. That was a real revelation."

The agricultural and medical products target the same enzyme in the fungus. Hylke Kortenbosch, a Ph.D. candidate supervised by Snelders, discovered that two resistant variants of Aspergillus, TR34 and TR46, differ in their distribution in the air across the Netherlands. TR34 was already found throughout the country, while TR46 was more common in agricultural areas with many flower bulb fields and greenhouses.

Now there is another cause for concern. These resistant variants of Aspergillus often also prove resistant to fungicides from two other chemical classes used in agriculture. These fungicides are not used in medicine, but they can still help maintain resistance to antifungal medicines. According to Kortenbosch, this makes the problem even more complex. "In agriculture, we are creating an environment in which natural selection favors the fittest fungi, those carrying multiple forms of resistance. The genes hitchhike together."

In his own backyard

Kortenbosch then investigated whether different fungicides could maintain resistance. For this, he used mown, unsprayed grass from his own backyard. In glass bottles, he grew resistant and nonresistant Aspergillus fungi on the grass, with and without the addition of different fungicides.

The experiment showed that even fungicides that are not azoles gave azole-resistant fungi an advantage. The researchers conclude that banning azoles in agriculture alone would not be enough to solve the resistance problem quickly. Because different resistance genes hitchhike together, other fungicides can help maintain resistance to medical treatments.

New medicine, same problem

For this reason, Snelders is deeply concerned about the development and use of new fungicides, including a new class that inhibits the enzyme DHODH. The antifungal drug olorofim is being developed to treat serious fungal infections, including those caused by Aspergillus. The agricultural fungicide ipflufenoquin targets the same enzyme. Snelders fears that the pattern of resistance development will repeat itself.

"What you really want is to have a separate class of medicines reserved for treating Aspergillus infections in vulnerable patients, without that same class also being used in agriculture."

According to Snelders, tackling resistance requires a broad approach in which all parties involved need to take responsibility. "Stopping the use of these products is not easy. It is a complex problem, and we are locked into a system. But we want to keep drawing attention to it and continue urging everyone involved to take responsibility. The problem will not go away on its own, and reducing the use of fungicides in agriculture is important."

Publication details

Hylke H. Kortenbosch et al., Non-triazole agricultural fungicides indirectly select for triazole resistance in the human pathogen Aspergillus fumigatus, Current Biology (2026). DOI: 10.1016/j.cub.2026.10.033

Journal information:
Current Biology

Provided by
Wageningen University

Citation: Genetic hitchhikers make Aspergillus infections even harder to treat (2026, November 9) retrieved 9 November 2026 from https://phys.org/news/2026-11-genetic-hitchhikers-aspergillus-infections-harder.html