Screwworms impacting cattle trade

On November 22, 2024, Mexico’s Chief Veterinary Officer confirmed the detection of New World Screwworm (NWS) in Chiapas, a southern Mexican state. This finding signals an alarming northward movement of this highly destructive pest (Cochliomyia hominivorax).

The North American Invasive Species Management Association (NAISMA) called the detection NWS a serious threat to the United States as well as Mexico. In the last two years the screwworm has spread from Colombia throughout Panama and into Costa Rica, Nicaragua, Honduras, Guatemala—and now Mexico.

USDA responded by immediately closing the U.S./Mexico border to all movement of northbound live cattle.

“The discovery of NWS in Mexico poses a severe threat to the U.S. livestock industry, wildlife, and public health,” said NAISMA. “Left unchecked, NWS infestations could spread further north, jeopardizing ecosystems and causing devastating economic impacts.”

NWS larvae infest the tissue of warm-blooded animals, including livestock, wildlife, and even humans. Larvae enter through open wounds and feed on the host’s flesh, causing infections that can be fatal if untreated.

Infestations of NWS are notoriously difficult to detect, and larvae appear only after significant damage to an animal has occurred.