The death toll from the tornado that destroyed much of Joplin has risen to 151, and three of the latest victims suffered from a rare fungal infection that can occur when dirt becomes embedded under the skin, authorities said.

Coroner Rob Chappel said Friday the three had been hospitalized with the unusually aggressive infection sometimes found in survivors of other natural disasters. He said it was difficult to identify the fungus as a cause of death since the people infected also suffered other severe injuries.

'We could visibly see mould in the wounds.'— Dr. Uwe Schmidt

"These people had multiple traumas, pneumonia, all kinds of problems," said Dr. Uwe Schmidt, an infectious disease specialist at Freeman Health System in Joplin. "It's difficult to say how much the fungal infections contributed to their demise."

Schmidt said his hospital treated five Joplin tornado victims for the infection, known as zygomycosis (zy'-goh-my-KOH'-sihs).

Jacqueline Lapine, a spokeswoman for the Missouri Department of Health and Senior Services, said the department has received reports of eight suspected deep-skin fungal infections among survivors of the May 22 twister. She said all of the victims had suffered multiple injuries and developed secondary wound infections.

Zygomycosis, also known as mucormycosis, is a sometimes-fatal infection that spreads rapidly and can be caused by soil or vegetative material getting under the skin. It's more prevalent in people with weakened immune systems or untreated diabetes but can affect healthy people who get badly hurt.

Schmidt said he had seen only two cases of zygomycosis in his 30 years of practice, and both of those cases involved people with untreated diabetes.

Extensive wounds

Among the tornado survivors, some wounds that were stitched up had to be reopened because they had not been adequately cleaned, Schmidt said.

Overall infection numbers were not available. The health department in Springfield-Greene County, where some patients were treated, declined to release information about patients sickened by the fungus, citing patient privacy concerns.

The Springfield News-Leader reported that the department sent a memo Monday to area health providers warning them to be on the lookout for the infections.

In the aftermath of the tornado, Freeman Health System treated more than 1,700 patients. Doctors from St. John's Hospital, which was badly damaged by the twister, treated patients at makeshift facilities.

"These were very extensive wounds," Schmidt said. "They were treated in the emergency room as quickly as possible."

A week after the tornado, patients began arriving with fungal infections.

"We could visibly see mould in the wounds," Schmidt said. "It rapidly spread. The tissue dies off and becomes black. It doesn't have any circulation. It has to be removed."

Schmidt said the infection is sometimes seen in survivors of mass trauma such as the 2004 tsunami in Indonesia.

"This fungus invades the underlying tissue and actually invades the underlying blood vessels and cuts off the circulation to the skin," he said. "It's very invasive."