GoKawiilThe diarrhoea-causing parasite Cyclospora cayetanensis reproduces through egg-like structures called oocysts (stained orange in this microscope image).Credit: CDC/DPDx - Melanie Moser
A microscopic parasite found in contaminated food products is ruining summer meals across the United States in the largest outbreak of its kind in the country’s history. And health officials have yet to identify the source, although the state of Michigan, which has reported the highest number of infections, has signalled that lettuce or salad greens might be the culprit.
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Since 1 May, 1,645 infections with the parasite Cyclospora cayetanensis have been confirmed, and more than 5,100 further cases are under investigation. These figures — which have accumulated in just a few weeks — have quickly surpassed the total number of cases typically seen in a year, says Joel Barratt, a molecular parasitologist at Emory School of Medicine in Atlanta, Georgia. More than 100 people with C. cayetanensis infections have been hospitalized, but no deaths have been reported.
One issue that is probably impeding the investigation is that “the number of staff working on these outbreaks is not what it used to be”, says Barratt, who worked at the US Centers for Disease Control and Prevention (CDC) in Atlanta for eight years and led the parasite surveillance team there. Barratt left the agency ten months ago, after the administration of US President Donald Trump fired employees or encouraged them to leave in a bid to downsize the government.
Nature spoke to Barratt and Jitender Dubey, a microbiologist at the US Department of Agriculture in Beltsville, Maryland, to learn more about the outbreak and how health officials are responding.
How does Cyclospora make people unwell?
C. cayetanensis is an intracellular parasite, meaning that it invades and then hijacks a host’s cells, especially those in the lining of the intestines. Once inside, it rapidly begins to multiply, which damages the cells. It can take a week or more for the parasite to complete its life cycle and inflict enough harm for symptoms to appear.
The hallmark symptom of watery diarrhoea occurs because the parasite inflames the intestinal lining. This disrupts the body’s ability to absorb water and nutrients, and causes the body to flush excess fluid through the gut. Although the infection usually runs its course when the immune system expels the parasite from the body — meaning that most people will not require treatment — the illness can last for weeks or even months.
The main treatment that physicians use to fight the parasite is the combined antibiotic trimethoprim–sulfamethoxazole (sold as Bactrim). Antibiotics are not typically used against parasites, but Bactrim starves Cyclospora of an essential vitamin it needs to replicate.
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