The New World screwworm, a parasitic fly whose larvae consume living tissue, is advancing northward with the warming climate. British entomologists from the University of Southampton are pioneering genetic control methods to halt its spread, even as Canada imposes an emergency ban on cattle imports from Texas, where an outbreak has infected livestock and a handful of humans.
Dr. Helena Vance, Science & Climate Correspondent: The situation is a textbook example of how climate change amplifies biological threats. The screwworm, Cochliomyia hominivorax, was historically confined to tropical Latin America. But rising minimum winter temperatures have allowed it to establish footholds in the southern United States. In June, a rancher in Hidalgo County, Texas, reported a calf with a weeping wound. Beneath the surface, 200 screwworm larvae were consuming its flesh. The U.S. Department of Agriculture confirmed the first U.S. outbreak in 30 years.
Canada’s response was swift. On Tuesday, the Canadian Food Inspection Agency halted all live cattle imports from Texas, fearing the parasite could decimate its own beef industry. But the problem cannot be contained by borders alone. The screwworm fly can travel 200 kilometres in a single migration, and its larvae hitches rides in animal wounds. Climate models project the species will reach the Canadian prairies within two decades if emissions continue unabated.
This is where British science enters. Researchers at the University of Southampton’s Institute for Life Sciences have developed a gene drive that targets the screwworm’s female fertility. The technique, published in Nature Communications last month, uses CRISPR to insert a gene that makes female flies sterile. When released into the wild, these modified insects mate with normal males, and the sterility gene spreads through the population. In laboratory trials, the gene drive achieved 95 per cent population collapse within five generations.
Dr. Emma Lockwood, lead author of the study, put it simply: ‘We are giving evolution a nudge. The screwworm is a brutal creature, but it is also vulnerable. Its life cycle is short, and it breeds fast. We can turn that against it.’
The method is not without controversy. Environmental groups have raised concerns about unintended ecological impacts, but Lockwood is adamant: ‘The alternative is a world where screwworm infests cattle, dogs, and humans from Texas to Toronto. We cannot afford paralysis.’
The urgency is underscored by the human toll. In Texas, three cases of cutaneous myiasis have been reported in farm workers, with larvae burrowing into wounds and natural openings. Without treatment, the infestations can lead to sepsis and death. The current outbreak has been contained with insecticide sprays and sterile insect technique releases, but these are stopgap measures.
The broader pattern is clear. As the planet warms, pathogens and parasites are shifting poleward. The screwworm is just one of many. The British team’s work offers a template for dealing with such threats, but it requires a commitment to field trials and regulatory approval. The Canadian ban buys time, but time is precisely what we are running out of. The science is sound. The tools exist. The question is whether our political systems can deploy them fast enough.
For now, the world watches a small team in Southampton as they prepare for the next phase: a controlled release on a Caribbean island to test the gene drive in the wild. If it works, the screwworm’s northward march may be halted. If it fails, the cattle industry of North America faces a future of perpetual vigilance. The climate does not negotiate. Neither should we.
