Illegal horse trafficking across the U.S.-Mexico border is raising concerns that gaps in border enforcement could make it harder to contain the return of the New World screwworm, which is a flesh-eating parasite that threatens livestock.

A Reuters investigation found that horses and other animals continue to cross the border illegally, bypassing the veterinary inspections, health certificates and quarantine procedures required for legally imported livestock.

In one case, Texas sheriff's deputies intercepted a trailer near Redford in May carrying six horses that had been smuggled across the Rio Grande. 

The horses were not infected with screwworm, but authorities have said that the incident illustrates how animals can enter the country outside of the safeguards designed to prevent the spread of disease.

The New World screwworm was eradicated from the United States decades ago, but it has recently returned to the region. 

More than 2,000 equine cases have been reported in Mexico since the current outbreak began in 2024, Reuters reported.

The parasite is particularly dangerous because its larvae feed on the living tissue of animals, potentially causing severe wounds and death. 

Experts warned that infected animals that are moved across borders could allow the pest to spread faster than it would naturally.