Changing Climate May be Moving a Subtropical Disease North

Aug 7, 2019

Pythium Pathogen grown from Chincoteage water samples.
Credit Erica Goss

At Chincoteague National Wildlife Refuge on the Eastern Shore, a herd of wild ponies is under attack by a deadly infection.

So far, eight female ponies have died, and the volunteer fire department that owns the herd is fighting to prevent additional deaths.

The microorganism that causes the disease known as pythiosis thrives in wet, warm regions of the world.

Local veterinarian, Charles Cameron has been treating the ponies since the disease first appeared three

Veterinarian Charles Cameron
Credit Pamela D'Angelo

years ago. He says another pony began exhibiting the disease's tell-tale lesions in July.  "This was unusual," Cameron notes. "Normally it's the latter part of August and September in the past that we've seen the lesions. It's a factor of temperature, warm weather and stagnant water. The last few years we've had pretty wet springs, a lot of standing water and warm weather."

Erica Goss, a scientist from the University of Florida, is taking water samples throughout the refuge to help map the spread of the micro-organism known as pythium insidiosum.  "We got some samples from Chincoteague in June, and some of the water temperatures where those water samples were taken were up to 100 degrees. And this pathogen thrives in the wet. It can only reproduce and spread when there's available water. So, as the summers become hotter and wetter, we do expect it to be more prevalent in the environment," Goss predicts.

Refuge Manager Nancy Finley is counting on science and medicine to prevent more cases of the disease. "There's two fronts. We're trying to find out where the organism is, what habitat it might hang out in. And then there's the other front the fire company is taking the lead on, which is to find out what's going on with the health of the horses and what we can do to prevent the disease through vaccines or treatments."

Researcher Gustavo Machado examines a water sample.
Credit Pamela D'Angelo

Scientists are also sampling fresh water reservoirs the refuge built to provide habitat for migratory waterfowl. Gustavo Machado, a scientist from North Carolina State University who studies the evolution and spread of infectious diseases in swine, poultry and horses, is assisting the effort.

Machado says the microorganisms living in the refuge may enter a pony's body through a bug bite or a cut. "It's super hard to tell, exactly. There's not much research on that. That's one of the reasons why we're here trying to understand more or less how this is actually spreading in this area."

Machado, Goss and Finley believe the organism may be found naturally throughout the Eastern Shore.  "It's an organism that's in the environment," Finley notes.  "So, there may be the same organism here as there may be in Chincoteague itself or anywhere else in the Eastern Shore."

Just an hour's drive north of Chincoteague, in Assateague Island National Seashore, a park ranger waves wild ponies away from the state road that leads into the park. Here, the ponies have free range.

Wild ponies on Assateague Island.
Credit Pamela D'Angelo

Allison Turner is a biological technician who helps maintain the herd. She says they've had no cases of equine pythiosis here.  "We do monitor the horses, do a complete survey six times a year. And we have so many people that out there very interested in them and they're looking at them all the time. So, if this was to show up in our population we would see it," Turner believes.

She says the habitat is different here. Water holes are small and widely spaced, and salt water washes in. Pythium can't live in salt water.  "So that would prevent the spread of it. That's speculation,," Tuner admits. "We don't know that for a fact but that could be the reason we don't have it up here. We don't know, we really don't know."

Back at the Chincoteague Refuge, Gustavo Machado has already used data to map out areas he considers hot spots for the microorganism. Pythiosis is normally found in tropical and subtropical places like Brazil, where Machado is from. He will look at how climate change might affect the spread of the organism along the Eastern Shore.  "With climate change there is a possibility to try to project to the future to see where within this region this is going to be more likely to be present. So still a lot of work to be done one that," he admits.

The team hopes to return to continue their research in the fall.

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