Famed Chincoteague wild ponies face own lethal disease

Pamela A D’Angelo

THE WASHINGTON POST – More than three years ago, members of the Chincoteague Volunteer Fire Company noticed unusual lesions on the legs of one of the shaggy, stocky wild ponies that have made this barrier island a year-round tourist destination.

The bright coral wound was treated and it seemed to be healing, but in a little over a week the mare became too weak to stand and had to be euthanised.

Seven more ponies followed in the coming years – the majority during the very wet 2018 – all succumbing to a deadly disease called swamp cancer.

Spread by a fungus-like microorganism that lives in stagnant water such as swamps, ponds and lakes, swamp cancer has been found worldwide. It frequently infects horses and dogs and thrives in tropical and subtropical regions.

Pythium insidiosum was first documented in the United States (US) in Texas and Florida about 60 years ago (under a different name). Scientists are still learning about how it spreads and infects. But one thing scientists do know is that with a warming climate, it is moving north – including to the island of Assateague, where the wild ponies live.

Wild ponies at Chincoteague National Wildlife Refuge in 2018. PHOTO: THE WASHINGTON POST

“Preliminary results show it’s fairly ubiquitous across the refuge,” said Nancy Finley, refuge manager.

Even so, there may be some good news this year.

Facing a threat to the herd of about 160 ponies and foals, the fire department, which owns the animals, last year turned to an experimental three-phase vaccine to inoculate the animals.

And while it is too early to declare victory, officials say the treatment may have paid off. During the recent annual spring pony roundup for health checks on April 18, all 148 ponies and 12 foals showed no sign of the disease, said Charles Cameron, the veterinarian who treated the ponies for 30 years and still helps during the check-ups.

Richard Hansen, the research veterinarian whose small Oklahoma-based company created the vaccine, is “cautiously optimistic” the vaccine is working.

The Chincoteague refuge sits within Assateague Island National Seashore, a 37-mile-long barrier island that runs from Ocean City, Maryland, south to about six miles beyond the town of Chincoteague, Virginia.

There are woodlands, marshes and miles of pristine beach and dunes that bring wildlife and tourists – especially each July when the ponies are herded across the channel between Assateague and Chincoteague islands and the foals are auctioned off to support the fire department and keep the herd size at about 150 ponies. Puddles of fresh water that attract migratory species of birds can get as hot as 100 degrees during the summer.

That’s a perfect environment for equine pythiosis, said Erica Goss, a scientist from the University of Florida, who specialises in plant pathogens, or oomycetes, such as this one.

Last year, with the pony swim as a backdrop, Goss, refuge wildlife biologist Kevin Holcomb and Gustav Machado, a scientist from North Carolina State University, began taking water samples throughout the refuge.

Machado is using the data to help map the spread of the organism at the refuge. Goss took water samples using horse hair as bait to confirm the presence of pythium.