New Mexico’s Second Screwworm Case Expands U.S. Livestock Surveillance

New Mexico animal health officials confirmed the state’s second case of New World screwworm on September 18, intensifying surveillance around livestock and wildlife as federal and state agencies try to contain a pest with major implications for cattle movement and trade.

The infected animal was a horse in Grant County, according to the New Mexico Department of Agriculture and the New Mexico Livestock Board. Officials said the case was identified on September 17 and that a minimum 12.4 mile infested zone was being established around the affected location.

The response includes additional fly trapping, animal inspections and monitoring intended to determine whether the parasite has spread beyond the affected animal. New World screwworm larvae feed on living tissue and can infest livestock, wildlife, pets and, rarely, people.

USDA’s current screwworm status system shows that animal health controls are now directly linked to livestock movement. APHIS maintains temporary restrictions on some animal and animal product imports from regions affected by the pest, including Mexico.

Cross border cattle trade is also operating under tighter safeguards. USDA reopened the Douglas, Arizona port to cattle imports from Mexico on August 24 under a new joint protocol, while describing the reopening as the first step in a phased process that can be paused if animal health risks increase.

U.S. surveillance has expanded well beyond confirmed cases. USDA says more than 100 screwworm specific traps and lures have been deployed across high risk border areas, alongside existing insect trapping networks, while thousands of wild animals have been examined in Texas.

The trade significance is straightforward. A wider outbreak could affect cattle movements, inspection requirements and cross border livestock flows even where food safety itself is not at issue. USDA states that the U.S. food supply remains safe and that the current risk to people is very low.

For producers and livestock traders, the most important variables now are the geography of new detections, the size of designated infested zones and whether USDA changes port access or animal movement protocols as surveillance data evolve.