India, July 8 -- A parasitic infection known for triggering severe, "explosive" diarrhoea has surged past 700 confirmed cases in Michigan alone, according to state health officials, marking one of the largest and fastest-moving outbreaks of its kind in years and prompting a multistate investigation by federal authorities.

The outbreak of cyclosporiasis, caused by the microscopic parasite Cyclospora cayetanensis, has spread rapidly since it was first flagged in late June, when the Michigan Department of Health and Human Services reported roughly 170 cases across seven counties. By July 4, that count had jumped to 572. Two days later, it climbed again to 681, and by Tuesday, the state's tally had surpassed 700, a more than fourfold increas...