This summer, tiny Cyclospora parasites have wreaked havoc on the digestive systems of thousands of people in the U.S.It's the biggest outbreak of this parasite the U.S.has ever seen.
In a July 28 update, the Centers for Disease Control and Prevention counted 45 states reporting cases of cyclosporiasis — the disease caused by the parasite.Michigan is ground zero for cyclosporiasis, where more than 10,000 people have eaten something, likely lettuce, contaminated with microscopic pods containing Cyclospora parasites.These parasites rely on the digestive tracts of humans — and only humans — to reproduce.To get there, they've likely been hitching rides on crops from places where the parasite is relatively common, to the unwitting mouths of hungry people across the U.S.
Their complex biology contributes to why they're so hard to kick, leading to infections that can last for weeks or months.On the surface of an herb, vegetable or berry, Cyclospora parasites lie dormant in pods — called oocysts — that are virtually invisible to the human eye."It would take about a hundred of them, linked end to end, to fit across the head of a pin," says Vernon Carruthers, professor of microbiology and immunology at the University of Michigan Medical School.Once swallowed by a human, the oocysts make their way down the esophagus, to the stomach and then the intestines.
"The [oocysts] respond to signals in the gut, like body temperature, probably bile, digestive enzymes.This causes the parasites to be released," Carruthers says.For the latest stories on the science of healthy living, subscribe to NPR's Health newsletter.The parasites go straight for the lining of the small intestine, where they burrow in, taking over the cells to make copies of themselves.
"These grow from just a few of the parasites we would take in, to millions of parasites replicating inside our intestinal cells," Carruthers says.After a while, some of those parasites begin to differentiate into egg- and sp...