Senate Judiciary Chair Chuck Grassley urged Agriculture Secretary Brooke Rollins to develop a vaccine for New World screwworms after the parasite returned to the United States for the first time in six decades. Grassley said he had discussed the vaccine proposal with Rollins months before the recent outbreak confirmed in Texas.
Rollins rejected the suggestion from the Iowa Republican. The New World screwworm is a parasite that infests livestock and other animals, causing significant damage to agricultural operations.
The screwworm outbreak marks a major concern for the nation's cattle industry. The parasite was confirmed in a calf in south Texas, approximately 50 miles from the Mexico border, late last week. The last confirmed detection in Texas occurred in 1966. Federal officials have warned livestock owners for over a year about the parasite's progression through Mexico, where it has advanced more than 1,100 miles northward.
The screwworm fly's larvae feed on the blood of warm-blooded animals. While the risk to humans remains low, the parasite spreads quickly where large numbers of cattle and livestock are kept together. It was eliminated from the United States in the 1970s after causing tens of millions of dollars in losses.
Rollins defended her agency's response, insisting there is no threat of widespread infestation. She stated the Texas case represents the only confirmed detection so far and expressed confidence that the outbreak will not become established in the country. The agriculture secretary emphasized the flies pose no threat to food safety, though officials worry about potential shortages if the parasite takes hold in cattle and poultry populations.
In March, Rollins announced the USDA partnered with the Army Corps of Engineers and private company Mortenson Construction to build a new sterile fly production facility at Moore Airbase in Edinburg, Texas. This facility will support efforts to combat the spread.
The existing strategy relies on releasing sterile flies rather than vaccination. Female screwworm flies mate only once during their months-long lives, and eggs from sterile fly partners do not hatch. This approach significantly reduces the screwworm fly population over time.
Texas Agriculture Commissioner Sid Miller urged the Trump administration to intensify deployment of the screwworm adult suppression system, which combines attractants, bait, and targeted insecticides to reduce adult populations before sterile fly releases complete the eradication effort. Miller noted this approach was successfully deployed during previous eradication campaigns.
Past eradication efforts proved so effective that the United States closed its domestic facilities for breeding sterile flies, leaving only one facility in Panama. In Mexico, the high cost of medicines to treat screwworm cases has forced ranchers to use crude homemade measures, such as applying gasoline or lime to open wounds to remove the worms.