‘Swamp Cancer’ Is Killing Chincoteague’s Famous Wild Ponies

by | 01.02.2019 | 9:34am

Wild ponies that have made the Chincoteague and Assateague islands famous are in a fight for their lives — literally. To date, seven horses have died after developing serious infections from stepping in wetlands contaminated with Pythium insidiosum.

This bacteria causes pythiosis, a fungus-like infection of the hooves and legs. The organism enters small cuts on horses legs when they step into infected waters; some horses then grow lesions that swell into tumor-like growths. If not treated, the infection is fatal.

Dubbed “swamp cancer,” the malady usually strikes dogs and cats in subtropical areas, but the organism that causes it is moving north with climate change. The disease has been seen sporadically in the past, but not at current levels. Managers of the 150-horse herd are concerned that warmer weather will increase infections.

Complicating treatment is the fact that the ponies range on over 4,000 acres, making initial detection of the small sores nearly impossible. Once detected, managers have been using intensive treatment to try to help the infected horses, including surgically removing the infected tissue and immunotherapy. However, the affected animals were still euthanized when the infection could not be gotten under control.

A particularly bad case of pythiosis. Photo courtesy Danette Wells

An experimental vaccine is thought to be the herd's best chance at warding off pythiosis. While this vaccine would protect the herd of ponies, it would not take the pathogen out of the environment.

Read more at The Washington Post.

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