A University of Washington medical professor who moved to Botswana to alleviate a doctor shortage was killed when a crocodile dragged him from a canoe, his family and colleagues said.

Richard K. Root, 68, was on a wildlife tour Sunday of the Limpopo River after visiting a clinic in the area.

He was in a lead canoe with tour guides when the crocodile thrust from the water, grabbed him and pulled him under, said Steve Gluckman, medical director of the Botswana program. He was not seen again.

The tour guides were wary of hippos, but there had been no reports of crocodile attacks in the area, Gluckman said.

Root was a nationally known expert in infectious disease and the former chief of medicine at Seattle's Harborview Medical Center.

He had moved to the southern African nation only this month to train health care workers to deal with AIDS.