Equine infectious anemia, also known as swamp fever, spiked in the 1930’s and again in the 60’s and 70’s—and it was during the 70's when it infected almost half of the wild Chincoteague pony herd. The disease, spread primarily through biting flies, is characterized by episodes of fever, as well as swelling, weight loss, and loss of stamina. Some infected horses can go up to a year without displaying symptoms after their initial infection, which would make the disease difficult to observe in wild ponies. EIA has been around for centuries, but to this day there is no successful treatment and no vaccine available in the United States.
In 1973, the Coggins test, which determines if a horse is infected with EIA, was approved by the US Department of Agriculture. The Coggins test was used on Chincoteague ponies the very next year on two foals that were bought at Pony Penning and taken to New Jersey, where they began showing symptoms.
Upon this news, both the Chincoteague Volunteer Fire Department (who owns the ponies) and the Virginia Department of Agriculture moved quickly to assess the health of the wild herd. About 50 wild ponies came back with positive Coggins tests, and they were immediately quarantined in a pen near the fire station.
The Virginia Department of Agriculture wanted all of the infected ponies immediately euthanized, but the CVFD fought back. The destruction of the sick wild ponies would be devastating for the herd numbers and the size of the gene pool, not to mention the toll it would take on the image of the ponies and on the island’s tourism.
Virginia state veterinarian Dr. G.B. Estes was sympathetic to the situation and negotiated a deal between the CVFC and the Department of Agriculture.
“The foals from diseased horses will be tested in fall and winter, and if we can salvage the foals, then we have an agreement that the original ponies will be destroyed,” Estes told reporters.
The 35 surviving ponies with equine infectious anemia were put back on Assateague, but fenced off on the north part of Assateague. There was a “buffer zone” of three miles between them and the healthy ponies.
Two ponies infected with EIA and quarantined on Assateague in 1975. Photo by the Philadelphia Inquirer. |
In 1975, Estes reported that 24 foals had been born to the infected ponies, and none of them had signs of the disease. However, the damage to the herd had already been done: that year, only 25 foals were sold to private homes, down from 54 the year before.
Numbers began to bounce back in 1976, when about 40 foals were sold at Pony Penning. In reaction to the EIA outbreak, two Spanish mustang colts were donated to the herd by restaurant owner Bob Evans to strengthen both the population and the bloodline, and in 1976 the CVFC purchased more mustangs to released on the refuge.
The CVFC became vigilant about EIA. Early in 1992, one mare got a positive Coggins test, sparking concern, but tests of the other 140 members of the rest of the herd came back negative. Thanks to Coggins testing, EIA in the United States has decreased significantly—the swamp fever used to kill thousands of horses a year, but now the incidence rate is less than 0.01%.
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