This Podcast Will Kill You
This Podcast Will Kill You

Ep 216 Cyclospora: Explosive Diarrhea Everywhere

July 21, 2026

AI Summary

5 min read

In 1979, a British parasitologist in Papua New Guinea found an unfamiliar parasite in routine stool samples from three patients. He could not name it. For the next decade and a half, researchers struggled to classify the organism—some thought it looked like fungal spores, others called it "cyanobacterium-like bodies." It was not until 1994 that the parasite received its official name: Cyclospora cayetanensis. The genus Cyclospora had been known since 1881, but every species described before 1994 infected only non-human animals—voles, reptiles, insectivores. The human-infecting species was a late discovery, and its recent recognition helps explain why most people have never heard of it, even as it now causes record-breaking outbreaks in North America.

The parasite’s life cycle and why it is so hard to kill

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What you'll learn

  • 1 (02:30) **Welcome & Episode Premise** - The hosts introduce a rapid-fire episode on Cyclospora, prompted by current news and listener requests, recorded on July 12th.
  • 2 (05:21) **What Is Cyclospora?** - The disease cyclosporiasis is caused by the parasite *Cyclospora cayetanensis*, an apicomplexan related to malaria and toxoplasmosis that only infects humans.
  • 3 (09:30) **The "Old Poop" Mystery** - The oocysts shed in stool are not immediately infectious; they must sporulate and mature in the environment for at least a week before they can infect a new host.
  • 4 (12:02) **Symptoms and Timeline** - After an incubation period of about one week (range 2-14 days), symptoms include explosive, foul-smelling, watery diarrhea, often described with the word "explosive" in the literature.
  • 5 (16:59) **Treatment, Resolution, and Severity** - The illness is usually self-limited and treatable with the antibiotic trimethoprim-sulfamethoxazole (Bactrim), which works by blocking folate synthesis in the parasite.
  • 6 (23:41) **The Surprising Recent Discovery** - *Cyclospora cayetanensis* was only identified as a human pathogen in 1979, and its final name wasn't established until 1994, despite the genus being known since 1881 in animals.
  • 7 (30:18) **The 1996 Wake-Up Call** - The first major North American outbreak in 1996, with at least 1,465 cases across 20 states and Canada, was definitively linked to imported raspberries from Guatemala.

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Show Notes

You’ve seen the headlines: a food-borne parasite is infecting people across the US, leaving them chained to the toilet sometimes for weeks on end, as they are ravaged by wave after wave of gastrointestinal upset. What the heck is cyclosporiasis and where did it come from? How scared should we be of our raspberries or lettuce or cilantro? To dish out the answers as fast we could, we put together this fact-filled episode about the biology of Cyclospora cayetanensis, how this parasite makes you sick, when we first learned about it (more recently than you might think), and what we know about this current outbreak (or outbreaks). We also probe how recent changes to foodborne pathogen surveillance on a national scale are contributing to the challenges in understanding the scope and origin of outbreaks such as this. You don’t want to miss this one!

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