Rare emerging disease claims Texas girl's leg: PCR plus sequencing identified culprit

The girl, otherwise healthy, presented to an urgent care facility with a 2-week history of a continuously enlarging erythematous bump on her lower leg, having reported recently swimming in an algae-filled pool. "Over the course of several weeks, what started as a very small lesion grew to involve most of her leg," says first author Stephen J. Salipante, of the University of Washington, Seattle. "Initial cultures of the wound suggested that this was a bacterial infection, and it was treated as such, but without success."

"She eventually needed to be hospitalized," says Salipante. Her treatment team at Cook Children's hospital tried increasingly aggressive medical and surgical management, including different antibiotic regimens, antifungals, and surgical debridements, but the infection simply didn't respond. "Given the microscopic appearance of the organism, our working hypothesis was that this was some kind of unusual, and very aggressive fungus," says Salipante.

However, sequencing a segment of DNA that is useful for categorizing fungi, the ITS1 sequence, "revealed that this was not a fungus at all -- rather, the DNA sequence very closely matched… P. insidiosum," says Salipante. This microbe has long been known to be a veterinary pathogen, primarily affecting horses and dogs, disfiguring them, often fatally. Only about 150 human cases have been reported in the literature -- nearly all of them in Thailand. "Needless to say, this was an unexpected result, as this young woman had not left Texas," says Salipante.

But "this organism did not demonstrate sensitivity in vitro to any of the antifungals or antimicrobials that had some activity for other isolates," says Murphey. Efforts at treatment even included trying an experimental therapeutic vaccine for Pythium-afflicted horses," says Murphey. "When it became clear to all of us that we were not going to clear the advancing local infection, we went on to amputation."

The amputation "undoubtedly saved this young woman's life," says Salipante. Now, nearly six months later, there is no vestige of infection.

"Pythiosis is believed to be an emerging human pathogen, meaning that the number of cases are expected to go up in the future," says Salipante.

"We have demonstrated that molecular identification by PCR screening and DNA sequencing provides a strategy to allow definitive identification of a range of pathogens, even unsuspected ones," says Salipante.

"DNA sequencing is a not just a tool for discovery anymore -- it provides critical data for making decisions impacting patient care," says coauthor Brad T. Cookson of the University of Washington. "I would add that medical care currently offers patients something very special -- our report demonstrates the vitality and utility of collaborative, transdisciplinary approaches for solving challenging medical problems."