The United States has temporarily suspended imports of cattle from Mexico following the detection of New World screwworm, a flesh-eating parasite that poses a severe threat to animals and, in some cases, humans. The decision was made after an infected cow was identified at a livestock inspection checkpoint near the border with Guatemala, signaling the pest’s northward spread.
The U.S. Department of Agriculture (USDA) has imposed immediate restrictions on the importation of live cattle and bison originating from or transported through Mexico. This suspension is expected to impact U.S. beef production and could influence market prices. The New World screwworm, named for its burrowing behavior resembling a screw being driven into flesh, was last seen in the United States during a 2016 outbreak in Florida.
The U.S. heavily relies on cattle imports from Mexico and Canada to supplement domestic herds, which have suffered declines in recent years. In 2023, imports of Mexican cattle surged by 43%, totaling 1.25 million head and comprising approximately 3.7% of the U.S. calf crop. This new restriction could exacerbate existing challenges in rebuilding cattle herds.
The USDA’s Animal Plant and Health Inspection Service (APHIS) has halted imports while it collaborates with Mexican veterinary officials to assess the extent of the infestation. Efforts are underway to prevent the screwworm from entering the United States and mitigate its spread. APHIS has also intensified regional partnerships to address the pest in areas already affected.
New World screwworm is endemic to regions in the Caribbean and South America but has recently expanded its range, with cases reported as far north as Honduras, Costa Rica, and now Mexico. APHIS has maintained a barrier zone in Panama since 2006 to prevent the pest’s spread into Central and North America. However, detections have surged significantly in recent years, with more than 6,500 cases reported in Panama in 2023 alone, compared to an average of 25 cases annually in previous years.
The screwworm’s larvae are particularly damaging, feeding on warm-blooded animals and causing severe tissue damage with their sharp mouth hooks. They infest wounds, burrowing deeper as more larvae hatch, which can lead to severe injuries, secondary infections, and even death if untreated. The pest’s lifecycle and feeding behavior make eradication efforts complex and resource-intensive.
APHIS has allocated nearly $110 million to combat the pest’s spread and reestablish the protective barrier in Central America. This funding will support eradication campaigns, monitoring, and collaborative efforts with affected countries. The recent detection in Mexico underscores the need for urgent action to protect North American agriculture and prevent further incursions.
The last significant outbreak of New World screwworm in the United States occurred in 2016 in Florida. It was eradicated through an intensive campaign that included the release of 154 million sterile flies, a method that has proven effective in controlling screwworm populations. Sterile insect techniques involve the mass release of sterilized male flies, which mate with wild females, resulting in non-viable eggs and a gradual reduction in the pest population.
The reemergence of the pest highlights the growing challenge posed by changing land use patterns and increased cattle movement in the region. More farmland and livestock transportation have likely contributed to the northward spread of screwworm. Authorities emphasize the importance of proactive measures and regional cooperation to prevent the pest from causing widespread damage to livestock and human health.
Efforts to push the pest back into its endemic range and secure the protective barrier in Central America are ongoing. However, the immediate concern lies in addressing the economic and logistical challenges posed by the suspension of Mexican cattle imports. Balancing the need to protect U.S. agriculture while maintaining a steady supply of livestock will require careful management in the coming months.
