A microscopic parasite is behind a summer wave of “explosive” diarrhea spreading across the United States. Health officials are tracking a sharp rise in cases, and while it sounds alarming, the illness is usually treatable and rarely dangerous.

Cyclosporiasis, a nasty parasitic infection that causes “explosive” watery diarrhea, has sickened dozens of people in Michigan and other parts of the United States.

Health officials in Michigan are investigating a “sudden and large” increase in cases of cyclosporiasis, the Michigan Department of Health and Human Services said.