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 noted that lettuce or salad greens could be the culprit.

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Since May 1, 1,645 parasite infections Cyclospora cayetanensis More than 5,100 additional cases have been confirmed and are being investigated. These numbers, 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 do. cayetanensis Those infected have been hospitalized, but no deaths have been reported.

One problem that is likely hampering research is that “the number of staff working on these outbreaks is not what it used to be,” says Barratt, who worked at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta for eight years and led the parasite surveillance team there. Barratt left the agency 10 months ago, after U.S. President Donald Trump’s administration laid off employees or encouraged them to leave in an attempt to reduce the size of the government.

Nature He spoke with Barratt and Jitender Dubey, a microbiologist at the U.S. Department of Agriculture in Beltsville, Maryland, to learn more about the outbreak and how health officials are responding.

As cyclospora make people feel bad?

C. cayetanensis It is an intracellular parasite, meaning it invades and then hijacks the host’s cells, especially those found in the lining of the intestines. Once inside, it begins to multiply rapidly, which damages the cells. The parasite may take a week or more to complete its life cycle and inflict enough damage for symptoms to appear.

The characteristic symptom of watery diarrhea occurs because the parasite inflames the intestinal lining. This disrupts the body’s ability to absorb water and nutrients and causes the body to eliminate excess fluid through the intestine. Although the infection usually runs its course as the immune system expels the parasite from the body (meaning most people will not need treatment), the illness can last weeks or even months.

The main treatment doctors use to combat the parasite is the combination antibiotic trimethoprim-sulfamethoxazole (sold as Bactrim). Antibiotics are not usually used against parasites, but Bactrim starves them cyclospora of an essential vitamin that it needs to replicate.

As cyclospora get into food?

TO cyclospora Infection means that someone has consumed food or water contaminated with human feces. DO. cayetanensis It reproduces through egg-like structures called oocysts that are shed in human feces. These oocysts are not immediately infectious: they must first sporulate, or mature, in a warm environment at temperatures between 22°C and 32°C for a week or two, which is one reason why outbreaks tend to occur during the summer.

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Although DO. cayetanensis Although it is most common in tropical climates and past outbreaks in the United States were frequently linked to foods imported from those regions, it is increasingly becoming a domestic problem. Recent US outbreaks in 2018 and 2020 were linked to produce likely grown in the United States, indicating that the parasite’s reach is expanding beyond regions where it has been historically endemic.

Pollution usually occurs from sanitation failures, Barratt says. For example, untreated wastewater could contaminate agricultural soil. Or farmworkers who lack immediate access to toilets may defecate in or near crop fields.

What worries Barratt, however, is the increase in outbreaks that scientists are seeing. “They seem to be increasing year after year,” he says. Research suggests that climate change, which is creating warmer environments for the parasite’s oocysts to mature, could be partly to blame.¹.

More studies on how latrines are used on farms and regular surveillance of farmworker feces could help explain how these outbreaks start, Dubey says, as well as research into whether infected but asymptomatic people can transmit the parasite.

How are researchers trying to determine the origin of the outbreak?

Tracking the parasite requires coordination between U.S. federal and state health officials. First, state laboratories collect fecal samples from people with symptoms of illness and send them to federal facilities. If a sample tests positive for cyclosporaHealth officials will determine when the person started showing symptoms and record what they ate in the previous weeks.