Increased Vigilance Needed for Potential New World Screwworm Infestation in the United States

By Leslie Barlow, EDCC Communications Manager

The detection of New World Screwworm in November of last year in a cow in the southern Mexico state of Chiapas has set off cautionary alarms on this side of the border. 

According to the United States Department of Agriculture Animal Plant & Health Inspection Service (APHIS), New World Screwworm (NWS) is a devastating pest of livestock. It is not currently in the United States, but it is present in Central and South America and has been recently moving northward. 

NWS maggots can infest livestock and other warm-blooded animals, including people. They most often enter an animal through an open wound or mucous membranes and feed on the animal’s living flesh. NWS larvae do not feed on dead tissue or carrion. Untreated screwworm infestations can be fatal. 

The Equine Disease Information Center (EDCC) has created an NWS page and Owner Factsheet at https://www.equinediseasecc.org/new-world-screwworm.

APHIS is currently restricting the import of livestock, including horses, into the United States from Mexico. Import requirements for horses, once established, will reflect the current import screwworm protocol for horses from other screwworm-affected countries to mitigate introduction of this disease.  However, there are other ways this infestation could be introduced into the United States. For example, APHIS is aware that equids are illegally transported or stray into the United States from Mexico.  To protect livestock, APHIS is encouraging horse owners to be aware of the signs of NWS infestation. 

• Check pets and livestock for draining or enlarging wounds, and signs of discomfort such as irritated behavior and headshaking.
• Also look for screwworm larvae (maggots) or eggs in wounds. Screwworm eggs are creamy and white and are deposited on or near the edges of superficial wounds. 
• This pest can infest a wide variety of wounds, from tick bites to cuts and dehorning or branding wounds. 
• Infestations are very common in the navels of newborn animals, nasal or eye openings, and genitalia.
• If an animal is suspected to be infested with screwworm, immediately contact your veterinarian, state animal health official, or an APHIS veterinarian. 

The EDCC is an industry-driven information center which works to protect horses and the horse industry from the threat of infectious disease in North America. The center is designed to seek and report real-time information about diseases similar to how the Centers for Disease Control and Prevention Center (CDC) alerts the human population about diseases in people. The EDCC is based in Lexington, Ky., at the American Association of Equine Practitioners headquarters, with a website hosted by US Equestrian. The EDCC is funded entirely through the generosity of organizations, industry stakeholders, and horse owners. To learn more visit www.equinediseasecc.org