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A parasite inflicting bouts of explosive diarrhoea across the US is at risk of going under the radar if it spreads to Australia, a leading expert has warned, due to complacency and a lack of training and research focused on parasitic diseases.
As of last week, 34 US states have recorded 1645 confirmed cases of cyclosporiasis, an infection caused by the microscopic Cyclospora parasite characterised by “loud”, “copious” and “explosive” bowel movements.
Authorities are investigating shredded lettuce used by Taco Bell and grown by Taylor Farms in Mexico as a possible source of a cluster of cases blowing out into the nation’s worst Cyclospora outbreak, months after the Trump administration cut the federal parasitic control lab from 11 staff to three.
While there has never been a widespread outbreak of Cylospora in Australia, the risk of the parasite getting into the country via imported produce or an infected traveller should not be downplayed, Professor Shokoofeh Shamsi, an expert in parasitology from Charles Sturt University, said.
“Geographically, we are a continent, so we have a natural biosecurity border around us – it takes time for things to come here. But it doesn’t mean we are 100 per cent safe,” she said. “We shouldn’t let our guard down.”
The hardy parasite could get into Australia via fresh or frozen produce from regions where the pathogen is common, including Central and South America and parts of Asia. Leafy greens, herbs and berries are often carriers.
Cyclospora and other parasites may not be top of mind for doctors diagnosing gastrointestinal illnesses, which have a broad number of causes, meaning cases may be initially missed, Shamsi said.
“And if we are lucky and there is a medical doctor that gets suspicious and tests for it, there is no obligation to report it because it’s not listed as a notifiable disease.”
Notifiable diseases are illnesses that pose elevated public health risks and must be reported to authorities if detected. No foodborne parasites are listed, said Shamsi, who believes the list requires a rethink.
“We are really good in Australia when it comes to bacteria and viruses, but I just don’t know why we became so complacent when it comes to parasites,” she said. “It’s like an unspoken agreement that we do not talk about them.”
The Department of Agriculture, Fisheries and Forestry is monitoring the US outbreak, a spokesperson said, but there was no current evidence of food linked to the outbreak being imported into Australia.
Julian Cox, an associate professor in food microbiology at the University of NSW, said the risk of cyclosporiasis in Australia is extremely low because of our tight biosecurity, and the fact much of our produce is domestically grown.
However, he said if the disease arrived, there may be a lag in detection or diagnosis. Doctors would only check for something like Cyclospora if the usual viral and bacterial suspects had been ruled out in a patient with gastro-like symptoms.
“They might look for salmonella and campylobacter and norovirus. Basically, a bunch of bad bugs. But Cyclospora would not be part of that routine.”
Parasites are harder to trace and detect compared to viruses and bacteria.
“If we were testing lettuces for salmonella, we can use a process called enrichment. What that does is allow a free-living organism like a bacterium to grow to higher numbers to make detection more reliable,” Cox said.
“The problem with parasites is that they have to grow on living cells, so we can’t use that laboratory enrichment technique to amplify the numbers.”
That’s part of the reason the outbreak spread rapidly in the US for weeks without a clear cause.
The problem of parasite control was also highlighted during a Cyclospora outbreak on two cruise ships out of Fremantle in 2010.
At least 73 people had lab-confirmed cases, and another 241 cases were suspected, possibly caused by fresh produce brought aboard in Malaysia or Singapore.
Scientists later noted cases may have been underreported because there was no “systematic” survey of the outbreak, and no confirmed source of the parasite was ever found.
Australia has also lost research expertise in parasitology over the past few decades, with more experts retiring than training as professors in the field, Shamsi said.
That means less parasitology is taught to student vets and doctors, and there are fewer researchers to answer questions about how well our medical system can respond to parasitic diseases.
It took more than a year for doctors to realise a Canberra woman complaining of fevers and depression had an eight-centimetre python worm in her brain in 2022, Shamsi said.
Scientists have also sounded the alarm over a lack of research attention on Toxoplasma gondii, a brain-invading parasite related to Cyclospora that infects one in three people.
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Angus Dalton is the science reporter for The Sydney Morning Herald.Connect via X or email.From our partners
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