On June 3, the United States Department of Agriculture (USDA) confirmed the presence of New World Screwworm (NWS) in a three-week old calf in Texas.
NWS is a flesh-eating parasite carried by a fly that lays eggs around open wounds in all manner of livestock as well as horses and humans. It can be severe and potentially fatal. Screwworms can be transmitted to animals and people who travel in endemic areas, have open wounds, or are around other livestock. All horses are susceptible to NWS but horses at higher risk for NWS are those with wounds, recent surgical sites, tick bite sites, and foals with fresh umbilical sites.
NWS requires immediate veterinary attention and must be reported to the appropriate state and federal authorities.
The Guidance
US Equestrian has issued a guidance document in which it says that it “expect[s] screwworm to continue to spread in the United States and encourage[s] horse owners to stay informed about its progress, even if the states they live and compete in do not currently have confirmed cases.”
If you arrive at a USEF-licensed competition from a state where screwworm has been confirmed, “your horse will need to be examined for any signs of wounds upon arrival to the competition grounds before they are permitted to enter the stabling area.” If the horse shows signs of a wound, then you will be required to “show veterinary records or a note on your health certificate indicating that you have treated the wound with an FDA authorized product for screwworm already, or treat the horse and provide that documentation to the competition and to USEF.”
These requirements apply to “horses who are hauling into the show but not stabling there.”
Other Resources
The Equestrian Disease Communication Center has created a page dedication to NWS, and you can follow NWS outbreaks on the Disease Alerts page.
The American Association of Equine Practitioners has created a New World Screwworm Working Group to examine preventative and therapeutic treatment options for NWS-infected horses, and also to investigate pesticides to control the screwworm fly around horses.
USDA prepared this graphic depicting the life cycle of the screwworm as we all this poster on what to watch for around the farm.
The USDA Animal Plant and Health Inspection Service produced a pamphlet with more detail including the economic impact of NWS and the history of US eradication efforts.
