A microscopic parasite that originates from contaminated food is causing quite a disruption this summer across the United States, marking the largest outbreak of its kind in the country’s history. Health authorities are still investigating the source, although Michigan, which has seen the highest infection rates, has indicated that lettuce or salad greens could be involved.
As of May 1, there have been confirmed cases of 1,645 infections due to the parasite Cyclospora cayetanensis, with over 5,100 additional cases currently under investigation. These numbers, collected over just a few weeks, have already exceeded the usual annual total, according to Joel Barratt, a molecular parasitologist at Emory School of Medicine in Atlanta. Over 100 individuals have required hospitalization, but thankfully, no fatalities have been reported.
Barratt notes that one major challenge in the investigation might be staffing, as “the number of people working on these outbreaks isn’t what it used to be.” He previously worked at the US Centers for Disease Control and Prevention (CDC) for eight years, and left ten months ago following cutbacks made under the Trump administration.
In a conversation with Barratt and Jitender Dubey, a microbiologist at the US Department of Agriculture, insights about the outbreak and the response from health officials were shared.
Understanding Cyclospora’s Effects on Health
C. cayetanensis is an intracellular parasite that invades the host’s cells, particularly those lining the intestines. Inside, it rapidly multiplies, causing damage. Symptoms can take a week or more to surface.
The primary symptom of this infection is watery diarrhea, which results when the parasite inflames the intestinal lining, disrupting the body’s ability to absorb fluids and nutrients. While the immune system usually manages to flush out the parasite, the illness can persist for weeks or even months.
Doctors typically use the combined antibiotic trimethoprim-sulfamethoxazole (known as Bactrim) to treat infections. While antibiotics are usually ineffective against parasites, Bactrim restricts Cyclospora from obtaining a necessary vitamin for replication.
How Cyclospora Contaminates Food
People get infected with Cyclospora by consuming food or water tainted with human feces. The parasite reproduces via oocysts — egg-like structures found in stool. However, these oocysts need to mature in warm conditions (between 22 °C and 32 °C) for about one to two weeks before they can cause infections, which is one reason outbreaks often happen in summer.
Although C. cayetanensis is commonly found in tropical regions, recent outbreaks in the US linked to domestically grown produce indicate the parasite’s expanding presence. Contamination generally stems from poor sanitation practices, such as raw sewage running into farmland or farm workers lacking proper access to facilities.
Barratt expresses concern over the rising number of outbreaks, noting, “They seem to be getting larger year by year.” He suggests that climate change may be contributing by providing warmer conditions conducive to the maturation of the parasite’s oocysts. Research indicates further investigation into how latrines are utilized on farms and monitoring of farm workers’ stool might shed light on the origins of these outbreaks.
Investigating the Outbreak’s Source
Pinpointing the outbreak involves collaboration between state and federal health officials. Initially, state labs gather fecal samples from symptomatic individuals and forward them to federal facilities. Upon confirming Cyclospora in a sample, health officials track the symptoms’ onset and document what the individual consumed in the preceding weeks.
