A 16-year-old daredevil inadvertently demonstrated the incubation period of a common roundworm-caused disease after she swallowed an earthworm at a friend's behest. The earthworm harbored larvae of the parasite, her doctors later concluded.
It took about 4 weeks for the young woman to develop a cough, wheeze, nausea, fever, and facial swelling.
Roundworms of the genus Toxocara are common in dogs and cats and annually infect about 10,000 people in the United States, mostly children who play in yards fouled with pet feces. Because infected kids are usually in frequent contact with the contaminated dirt, the parasite's incubation period in people has been difficult to assess.