Flesh-Eating Maggots Invade Mexico: USDA Issues Emergency Alert to Protect U.S. Livestock
On November 22, 2024, Mexico’s Chief Veterinary Officer informed the United States Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) about the detection of New World screwworm (NWS) in Chiapas, a southern Mexican state bordering Guatemala. This alarming find involved a cow at an inspection checkpoint, raising concerns about the pest’s potential spread into the United States.
New World screwworms are the larvae of a parasitic fly species that infest the living tissue of warm-blooded animals, including livestock, pets, and even humans. The infestation begins when the maggots enter open wounds, feeding on the host’s flesh and causing severe infections.
USDA Responds to the Growing Threat
Dr. Rosemary Sifford, Chief Veterinary Officer of the United States, emphasized the seriousness of the situation. “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,” she stated. “With this latest find in Mexico, we will further intensify this work to protect American agriculture and reestablish the barrier in Central America.”
In response to the detection, APHIS has immediately restricted the importation of animal commodities from or transiting Mexico. These trade restrictions will remain in place until Mexican veterinary authorities provide further information on the extent of the infestation. A complete list of screwworm-affected regions and trade restrictions is available on the USDA APHIS Animal Health Status of Regions website.
What to Watch For: Signs of Screwworm Infestation
Screwworm infestations can be challenging to detect early. Livestock producers, pet owners, and veterinarians along the U.S.-Mexico border are urged to monitor animals for signs of infection. Key indicators include:
Draining or enlarging wounds
Visible discomfort or restlessness
Screwworm eggs, which are creamy white and often found at the edges of superficial wounds
Screwworm larvae, which appear as small maggots in the wound area
If screwworm infection is suspected, producers and pet owners should contact a veterinarian immediately. Humans are rarely affected, but individuals who notice suspicious skin lesions should seek medical attention without delay.
A Northward Spread Fueled by Multiple Factors
Since 2006, APHIS has collaborated with Panama to maintain a biological barrier preventing NWS from moving northward from South America. However, the screwworm has steadily spread beyond the barrier, reaching Costa Rica, Nicaragua, Honduras, Guatemala, and now Mexico. Factors contributing to this expansion include increased farming in former barrier zones and higher cattle movements throughout Central America.
To combat the spread, APHIS has deployed sterile fly-release programs in strategic areas, utilizing aerial and ground methods to suppress screwworm populations. This method, proven effective in the past, remains a cornerstone of the eradication effort.
Protecting U.S. Livestock
APHIS is intensifying its collaboration with Mexican and Central American authorities to contain the infestation and reestablish the barrier in Panama. Meanwhile, livestock producers along the U.S.-Mexico border should remain vigilant, report potential cases promptly, and adhere to strict import regulations.
The fight against New World screwworm is critical to safeguarding American agriculture, livestock health, and public safety. APHIS continues to monitor the situation closely, deploying resources to ensure the pest does not gain a foothold in the United States.
