What is Fusarium graminearum, the fungus 2 Chinese researchers are charged with smuggling into the US?

The fungus spends the winter on infested crop residues like corn stalk or wheat straw.

(CNN) — Two Chinese researchers were charged with smuggling a fungus classified “as a potential agroterrorism weapon” that could decimate crops and impact human health into the US last summer in a wad of tissues, according to an FBI affidavit in support of the criminal complaint filed Tuesday.

Testing at an FBI laboratory discovered a sample containing the DNA sequence that “would allow a researcher to propagate live Fusarium graminearum,” a fungus that causes “head blight,” in the biological materials that Yunqing Jian, 33, and Zunyong Liu, 34, allegedly smuggled into the US, according to the complaint.

Fusarium head blight, or FHB, is a devastating disease for staple crops like wheat, barley, maize and rice. The fungus’ toxins can lead to “vomiting, liver damage, and reproductive defects in humans and livestock,” according to a news release from the US Attorney’s Office for the Eastern District of Michigan.

Jian and Liu were charged with conspiracy to commit offense or to defraud the United States, smuggling goods into the United States, false statements and visa fraud for bringing in the fungus Fusarium graminearum from China, the US Attorney’s Office for the Eastern District of Michigan said on Tuesday.

The criminal complaint does not allege that the defendants – who investigators say were in a relationship – had any plans to spread the fungus beyond the laboratory, but it said Liu was aware of the restrictions on the material and deliberately hid it in his backpack.

A devastating disease for staple crops

Fusarium graminearum is the most common cause of Fusarium head blight in North America and in many other parts of the world. The destructive disease, also called “scab,” has the capacity to “destroy a potentially high-yielding crop within a few weeks of harvest,” according to an article from the journal Molecular Plant Pathology published in 2004. It forms discolored lesions on the crops.

The US Attorney’s Office for the Eastern District of Michigan said the fungus “is responsible for billions of dollars in economic losses worldwide each year.” It is estimated that the losses for all crops in the Central United States and the northern Great Plains totaled $2.7 billion between 1998 to 2000, according to the article from the journal Molecular Plant Pathology.

The fungus spends the winter on infested crop residues like corn stalk or wheat straw.

Wet weather during the growing season causes the fungus to sprout spores, which are then windblown or water-splashed onto the spikes of wheat and barley, according to Gary Bergstrom, emeritus professor in the School of Integrative Plant Science Plant Pathology and Plant-Microbe Biology Section at Cornell University, who has previously published research on the head blight.

If wheat is infected during flowering, the fungus colonizes, killing the florets, and kernels don’t develop. If it is infected later, those plants produce diseased kernels that are shriveled and wilted.

Bergstrom told CNN the impact of the disease and the toxin each year is “like looking at the stock market. It goes up and down,” depending on weather patterns and other environmental details.

“But it has not gone away. The risk is still there. We do get losses every year,” he said Wednesday.

The United States Department of Agriculture (USDA) regulates the importation of organisms that might negatively impact agriculture in the United States, prohibiting anyone from importing any organism that “directly or indirectly injures, causes damage to, or causes disease in a plant or plant product” without first applying for and obtaining a permit from the USDA, according to the complaint in the case.

The USDA requires a permit for the importation of Fusarium graminearum. According to records maintained by the USDA, the Chinese researchers now charged never applied for, nor were issued, a permit to import the pathogen, the complaint said.

USDA permitting “is a mechanism that’s used all the time,” Bergstrom said. “We’ve used it in labs in our university and across the United States. It just takes a little time, like you’re applying for any application.”

Bergstrom said the danger with a pathogen being brought into the United States uncontrolled “would be if some new trait was introduced with a new strain that got out into the system.”

“Maybe it’s less sensitive to the fungicides we use, or maybe it has a particular strain, has a different spectrum of these fungal toxins that it produces,” Bergstrom said, noting that there is a tremendous variation in the fungus Fusarium graminearum in North America and across the world.

Bergstrom said that while he thinks the fungus is “kind of unlikely to be selected as an agent” for agroterrorism, “a lot of things are possible.”

“Some other things that don’t occur at all in the United States, that are on APHIS (Animal and Plant Health Inspection Service) watch list we are worried about … and would be an immediate serious concern,” Bergstom said. “I wouldn’t put that (Fusarium graminearum) in this category.”

Impacts on human and animal health

Grains infected with Fusarium graminearum have mycotoxins and eating them is “known to cause gastrointestinal disorders, skin irritation, and neuroendocrine changes,” according to a recent study by researchers in Poland.

In humans, the fungus has been linked to effects on the digestive system, including nausea and vomiting, Bergstrom said, and chronic exposure “has wide-ranging effects, including neurological disorders and immunosuppression,” according to the journal of Molecular Plant Pathology article.

The mycotoxins also impact animals, causing them to refuse food or develop diarrhea, haemorrhaging and irritated skin, the article said.

The predominant toxin associated with FHB infections in the United States is deoxynivalenol (DON), which is also known as vomitoxin because consumption can cause vomiting. The US Food and Drug Administration has established guidelines for DON levels in human food and animal feed. “Milling and baking further reduce vomitoxin levels. Brewing companies will not purchase grain with even a trace of a vomitoxin,” the USDA says. “In the unlikely event that vomitoxin ends up in the food supply despite all the industry safeguards, a person will have to eat enormous quantities of the product for the toxin to have any effect.”

Resistance to fungicides

Some research has shown that Fusarium graminearum is becoming “increasingly resistant” to fungicides, prompting the search for new fungicides “to effectively target FHB and reduce the pathogen’s ability to biosynthesize mycotoxins.”

“That’s something we need to monitor very closely,” Bergstrom said.

The researchers in Poland also noted that this increasing resistance warrants further research “to improve molecular methods for detecting fungicide-resistant strains and strains with a modified ability to produce mycotoxins,” and to introduce resistant wheat varieties that can effectively suppresses the development of Fusarium graminearum infections.

“We basically take an integrated management approach to these diseases,” Bergstrom explained. “There’s no one silver bullet. We don’t have a completely immune variety of plant, but we have some that are way more resistant than others.”

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