The presence of new world screwworm fly (NWS) has been confirmed in the United States by the US Department of Agriculture (USDA).
The US has been trying to keep the pest out of the country since last year and banned cattle imports from Mexico, where it was present, in a bid to do that.
The pest was confirmed in Texas in the navel of a three-week-old calf.
The screwworm is a species of parasitic fly that is known for the way in which its larvae – which are like maggots – eat living tissue.
Affecting livestock, pets, wildlife and, less commonly, people and birds, screwworm fly larvae burrow into the flesh of living animals, causing serious damage to livestock, as well as economic losses.
“Protecting our livestock industry is a national security issue of the utmost importance and USDA is wasting no time in taking action,” said Dudley Hoskins, under-secretary for marketing and regulatory programs.
“USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before and we will do it again.”
Control and eradication
Measures to contain and eradicate the pest include the establishment of a 20km infestation zone around the detection and the implementation of quarantines, movement controls and surveillance the area.
The US has also been releasing four million sterile flies per week into the air. These flies have been sterilised so that when they breed with a female fly, she lays unfertilised eggs and the screwworm population is reduced.
There will now be a targeted release of sterile flies by immediately deploying ground release chambers in the area.
The USDA will also increase its trapping for flies along the border and just outside of the dispersal area.
Food supply
The USDA has communicated that the food supply chain is safe, as screwworms do not infest meat, fruits, vegetables or other food sources.
It said that any evidence of screwworm infestation in an animal would be identified by the USDA’s Food Safety and Inspection Service (FSIS) and any contaminated product from an affected animal would not enter the food supply chain.
The USDA eradicated screwworm flies in the 1960s and it was contained to South America using sterile insect technology.
However, the pest began spreading northward and was detected in southern Mexico in November 2024.
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