Scientists Stalk a Microscopic Monster Killing Chincoteague's Famous Ponies

Aug 6, 2019

Veterinarian Richard Hansen inspects ponies.
Credit Pamela D'Angelo

For the past three years, a mysterious microorganism has been infecting the famous wild ponies of Chincoteague National Wildlife Refuge.

The infection is known as swamp cancer and it has killed eight female ponies so far.

The volunteer fire department that owns the herd and the U-S Fish and Wildlife Service, which oversees the refuge, have brought in scientists and veterinarians to try to eliminate the culprit and cure the disease.

At Pony Penning Day, the Chincoteague Volunteer Fire Department brings in the local veterinarian to examine its 142 horses. The next day, the young ponies are auctioned off. Fans crowd around the holding pens. This is the closest they will ever get to the scruffy, feral, and sometimes laser-blue-eyed Chincoteague ponies, some of which have lineages going back 400 years.

Fans of the Eastern Shore's wild ponies watch a vet check.
Credit Pamela D'Angelo

People come from all over the world for the annual event. Some watch the auction via livestream. Jeannie Zurich moved to Hebron, Maryland from New Jersey this year just to be closer to the ponies.  "So, now I'm only an hour away from here. That was the whole plan," Zurich admits.

Like Zurich, most here are hyper aware of the mysterious disease that has infected only fillies and mares. It was a park visitor who, last month, reported seeing an injured filly, the most recent victim of pythiosis, or swamp cancer. She didn't survive, despite receiving a series of a new vaccine meant to ward off the disease.

Richard Hansen is a research veterinarian from Oklahoma who developed the vaccine has vaccinated nearly all of the herd.  Like other scientists he's is trying to figure out why some horses don't get the disease.  "They seem to be, need to be, immunocompromised in some way for them to be susceptible," Hansen explains. "You could have two horses that may have wounds on them walk in the same pond and only one develop the disease because of some reason that we're still investigating."

University of Florida scientist Erica Goss works on Virginia's Eastern Shore.
Credit Pamela D'Angelo

Erica Goss is a scientist from the University of Florida where she specializes in plant pathogens like this one. It’s called an oomycete. It's basically a water mold but can behave like a fungus. It lurks in the refuge's shallow freshwater ponds and standing water used by migrating birds and the ponies.

To hear her describe the micro-organism, pythium insidiosum, is like listening to a science fiction horror story.   "It has these long filaments, so almost like these fingers that reach out into the tissue it infects to pull in nutrients, like plant roots. That's how it feeds itself," Goss says. "When it's reproducing it produces spores that swim in water. And so they swim until they find a host, and then they infect that host."

Hansen is using the same vaccine the Chincoteague ponies received to treat three human cases in Texas, Illinois and Georgia. A 3-year-old-girl and a 26-year-old man are cured, while a 14- year-old girl is still being treated.   "What you're trying to do is reverse the immune system so that it recognizes the infection," Hansen says.

At the refuge, the horses all check out healthy, but it may be too soon to know if the vaccine is working. As crowds watch the ponies, across the way, people wade in canals along the access roads catching crabs. Others head to the marshes across from the beach to fish.  "What we found in Florida is that this pathogen is really common in the environment," Goss notes. "It's in most of the lakes and ponds we sampled and I think that is probably true across the Gulf Coast. People use the lakes for recreation in Florida and it's not something we worry about."

As the fire department prepares for the next day's auction, Goss goes with a Fish and Wildlife biologist and a scientist from North Carolina State University to collect water samples throughout the refuge. They will use the data to build a map of infected waters.

This report, provided by Virginia Public Radio, was made possible with support from the Virginia Education Association.