GOLDVEIN, Va. – The United States recently imposed a temporary ban on the importation of cattle from Mexico – a major supplier of feeder cattle to the U.S. – following the detection of the New World screwworm at the lakeside town of Catazaja in southern Chiapas state in Mexico.

“Given the northward movement of New World screwworm, the USDA’s Animal and Plant Health Inspection Service (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 Rosemary Sifford, DVM, chief veterinary officer of the United States in Goldvein.

“With this latest find in Mexico, we will further intensify this work to protect American agriculture, and reestablish the barrier in Central America,” she added.

On Nov. 22, Sifford notified APHIS of a positive detection of New World screwworm in Mexico.

“The United States and Mexico are working on implementing measures to resume the normal flow of Mexican exports,” the Mexican government said in a statement.

Francisco Suárez Güemes, Mexico’s chief veterinary officer, notified APHIS, telling the agency the New World screwworm was found in a cow in Chiapas at an inspection checkpoint close to the border with Guatemala.

As a result, APHIS is restricting the importation of animal commodities originating from or transiting Mexico, effective immediately and pending further information from Mexican veterinary authorities on the size and scope of the infestation.

According to APHIS, New World screwworm maggots can infest livestock and other warm-blooded animals, including people. They most often enter an animal through an open wound and feed on the animal’s living flesh.

The name screwworm refers to the maggots’ feeding behavior as they burrow (screw) into the wound, feeding as they go like a screw being driven into wood, APHIS said. Maggots cause extensive damage by tearing at the hosts’ tissue with sharp mouth hooks. The wound can become larger and deepen as more maggots hatch and feed on living tissue.

As a result, New World screwworms can cause serious, often deadly damage to the animal. Adult screwworm flies are about the size of a common housefly, or slightly larger. They have orange eyes, a metallic blue or green body, and three dark stripes along their backs.

Although the USDA eradicated New World screwworm from the United States in 1966, using sterile insect technique, there is a constant risk of re-introduction into the United States, APHIS said.

Since 2006, APHIS has collaborated with Panama to maintain a barrier zone in eastern Panama, working to prevent the northward movement of New World screwworm from South America to New World screwworm-free areas in Central and North America.

In the last two years, New World screwworm has spread north of the barrier throughout Panama and into Costa Rica, Nicaragua, Honduras, Guatemala, and now Mexico, according to APHIS. This increase is due to multiple factors, including new areas of farming in previous barrier regions for fly control and increased cattle movements into the region.

APHIS is releasing sterile flies through aerial and ground release at strategic locations throughout Central America, and will continue working with partners in Mexico and Central America to eradicate New World screwworm from the affected areas, and to reestablish the biological barrier in Panama.

In addition, APHIS is working with partners in Mexico and Central America to stop the spread of New World screwworm into the United States, and is asking all producers along the southern border to watch their livestock and pets for signs of New World screwworm, and immediately report potential cases.

APHIS said New World screwworm infestations are difficult to detect at first. The agency advised producers to check their pets and livestock for draining or enlarging wounds, and signs of discomfort. Also, look for screwworm larvae or eggs.

New World screwworm eggs are creamy and white, and are deposited on or near the edges of superficial wounds, the agency added. If you suspect an animal is infected with New World screwworm, contact a veterinarian.

The newly imposed import ban is expected to have a significant impact on the U.S. livestock market, particularly on the supply of feeder cattle.

Josh Maples, University of Mississippi associate professor of agricultural economics, David Anderson, Texas A&M University professor of agricultural economics, and Charley Martinez, University of Tennessee assistant professor of agricultural economics, discussed this impact in a Nov. 27 joint analysis.

“The market impacts of this announcement are likely to be obvious in the near-term,” they said. “Roughly 5 percent of feedlot placements this year have been imported feeder cattle from Mexico. If the ban on imports of feeder cattle lasts awhile, it would mean a lower supply of feeder cattle going into feedlots. Tight feeder cattle supplies would get tighter, which would mean more support for prices. Right now, there are probably more questions than answers.”

Andrew P. Griffith, University of Tennessee assistant professor of agricultural and resource economics, however, told Farm World, “I do not expect this import ban to have much of an impact at all.

“The U.S. typically imports feeder cattle and calves,” he said. “A quarter of these calves are typically less than 500 pounds, which means they end up in stocker and backgrounding operations.

(Stocker cattle can range from 200-650 pounds, with the goal of providing a consistent pen of cattle to be sold to the next stage of the production line – the feedlot operation. Backgrounding is the growing of steers and heifers from weaning until they enter the feedlot for finishing).

“The main reason I do not expect much of an impact is because I expect the U.S. and Mexico will develop a protocol to continue cattle trade in a rather quick manner,” he added. “Thus, most of the cattle that get backed up will still make their way to the U.S. The quantity of cattle imported from Mexico is only about 3 to 4 percent of the U.S. calf crop size.”

When asked if the import ban will continue to affect all imported cattle from Mexico, he said, “It will affect all cattle until the two countries have established a protocol to reduce the risk of animals carrying New World screwworm.

“I just do not expect it to last long,” he added. “I would venture to guess they will have something figured out by the first of the year.”