The Department of Livestock Development and Thailand Equestrian Federation said zebras may be the source of the outbreak.
They asked everyone who owns a zebra to help prevent the spread of the disease.
All zebras must now be quarantined in covered stables with a very fine wire screen, 32 holes for an inch, to prevent disease carriers such as gnat and horsefly.
Owners of zebras can request the screen from the federation via 02-710-3166 or http://tefthailand.com website.
The department has told the zebra owners to strictly follow suggestions to protect the lives of horses in the country.