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With Screwworm Protocols in Place, US Resuming Livestock, Equine Imports From Mexico

A two-month suspension on cattle and bison imports from Mexico is expected to be lifted soon.

The change comes after implementation of a comprehensive pre-clearance inspection and treatment protocol meant to prevent New World screwworms (NWS) from entering the United States. The U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) made the announcement February 1.

APHIS temporarily suspended livestock imports from Mexico after that country detected NWS on November 22, 2024. The NWS fly, Cochliomyia hominivorax, is a species of parasitic fly whose tissue-eating larvae can infest any living mammal and cause severe damage, infection, and often death.

As part of the new protocol, cattle and bison will be inspected and treated for NWS—in addition to being dipped in a solution to ensure they are otherwise insect- and tick-free—by trained and authorized veterinarians prior to entering pre-export inspection pens in the Mexican cities of San Jeronimo and Agua Prieta, which have been APHIS inspected and approved.

There, the livestock will again undergo inspection by Mexican National Service for Health, Safety, and Food Quality (SENASICA) and APHIS officials before crossing at the Santa Teresa and Douglas ports of entry, respectively, according to the announcement.

Additional pre-export inspection pens and trade reopening through other ports of entry may come in the near future.

In the last two years, screwworm has spread north of the biological barrier established in Panama and into Costa Rica, Nicaragua, Honduras, Guatemala, El Salvador, Belize, and, most recently, Mexico. Multiple factors are behind the increase, according to APHIS, including new areas of farming in previous barrier regions for fly control and increased cattle movements into the region.

To eradicate NWS, APHIS is releasing sterile flies through aerial and ground release at strategic locations, focusing on southern Mexico and other areas throughout Central America. A complete list of regions APHIS recognizes as affected by screwworm, along with more detailed information on trade restrictions, can be found on the APHIS Animal Health Status of Regions website.

In related news, on January 21, APHIS resumed equine imports from Mexico with the implementation of a similar NWS safety protocol.

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Pat Hoffmann, Swine Technical Consultant at Elanco Animal Health tells us about the impact of New World Screwworm. The emergence of New World screwworm in the U.S. creates a threat for veterinarians, livestock producers and pet owners that has not been seen north of the Florida Keys since the fly was eradicated from the United States more than 50 years ago. New World screwworm (Cochliomyia hominivorax) larvae feed on living tissue and can affect a wide range of warm-blooded animals, including livestock, companion animals, wildlife, and even humans.
“New World screwworm could have a devastating impact on animal health, welfare, and producer livelihoods,” said Jeff Simmons, President and CEO, Elanco Animal Health. “We want to thank the FDA, EPA and USDA, for all their work to prepare for this threat. We’re committed to supporting our customers during this challenging time by delivering innovation, scientific expertise, and available resources to help treat New World screwworm and support the health and well-being of animals.”
Elanco is working alongside the U.S. animal health industry to help them fight against this parasite, offering a portfolio of options for pets and livestock that can help treat New World screwworm larvae infestations.