WASHINGTON – The chief veterinary officer of Mexico announced a positive detection of New World screwworm (NWS) in a cow in the southern Mexico state of Chiapas, at an inspection checkpoint close to the border with Guatemala. In response, the Animal and Plant Health Inspection Service (APHIS) of the US Department of Agriculture restricted the importation of animal commodities originating from or transiting Mexico effective immediately pending further information from Mexican veterinary authorities on the size and scope of the infestation.

A complete list of regions APHIS recognizes as affected by screwworm and more detailed information on trade restrictions can be found on the USDA APHIS Animal Health Status of Regions website.

NWS are fly larvae that infest living tissue of warm-blooded animals, causing infection. The maggots can infest livestock and other warm-blooded animals, including people, according to APHIS. They most often enter an animal through an open wound and feed on the animal’s living flesh. While they can fly much farther under ideal conditions, adult flies generally do not travel more than a couple of miles if there are suitable host animals in the area.

“Given the northward movement of NWS, APHIS has in recent months stepped up its efforts in Central America to partner with impacted countries to push this pest out of newly affected areas,” said Dr. Rosemary Sifford, chief veterinary officer of the United States. “With this latest find in Mexico, we will further intensify this work to protect American agriculture and reestablish the barrier in Central America.”

APHIS said the agency has collaborated with Panama to maintain a biological barrier zone in eastern Panama since 2006. The barrier was established to prevent the northward movement of NWS from South America to NWS-free areas in Central and North America. However, in the last two years, screwworm has spread north of the barrier throughout Panama and into Costa Rica, Nicaragua, Honduras, Guatemala and now Mexico, APHIS said. This spread is due to multiple factors including new areas of farming in previous barrier regions for fly control and increased cattle movements into the region.

In response to this movement, APHIS is releasing sterile flies through aerial and ground release at strategic locations throughout Central America.

APHIS is working with partners in Mexico and Central America to stop the spread of NWS into the United States, the agency said. All producers along the southern border are urged to watch their livestock and pets for signs of NWS and immediately report potential cases.

“Screwworm infestations are difficult to detect at first,” APHIS explained. “Check your pets and livestock for draining or enlarging wounds, and signs of discomfort. Also look for screwworm larvae or eggs. Screwworm eggs are creamy and white and are deposited on or near the edges of superficial wounds. If you suspect your animal is infected with screwworm, contact your veterinarian.”