The screwworm, like the measles, may have been forgotten by many, but it’s not new. And like the measles, which has cropped up in Texas recently, screwworm was once all but eradicated from the United States.
Infestations occur when a female fly lays eggs, between 10 and 400 at a time, on a fresh animal wound. Within a few hours, the eggs hatch into larvae that burrow and feed on the flesh. As the wound worsens, it attracts more flies, which lay more eggs. After about a week, adult screwworm flies can reproduce and begin the cycle all over again. The parasitic infection can kill a cow within two weeks if left untreated. There is currently no approved treatment.
Livestock, wildlife, pets and in rare cases, humans, can be affected.
In the 1950s, scientists discovered that radiation effectively sterilizes screwworm flies, and the federal government began an eradication program. A small outbreak in a deer population in the Florida Keys was snuffed out in 2017.
Now, a potentially bigger threat is approaching, migrating north from South America, where screwworm is endemic. It has been detected as close as 370 miles from Texas’ border, carried by the surge of animals coming through the Darién Gap, a once largely impenetrable jungle area that separates South and Central America. A joint eradication effort between the United States and Panama has largely kept screwworm south of Central America for decades. Illegal livestock transport and warm weather patterns have also contributed to the worm’s climb north, a spokesman for the Agriculture Department said.
The agriculture secretary, Brooke Rollins, announced in June an $8.5 million initiative based in Texas that will produce sterile male screwworm flies and then drop them into affected areas. Female flies mate only once in their lifetime, so the sterile flies eventually overwhelm and eradicate the pest.
Ms. Rollins also committed $21 million to renovate a fly production facility in Mexico, where 60 million to 100 million sterile male flies would be produced each week for use in Mexico or Texas by the end of the year.
But that effort would yield only about 20 percent of the sterile flies the United States would need to manage an outbreak, experts said. Around 600 million flies were released each week to eradicate screwworm decades ago. Senator John Cornyn, Republican of Texas, introduced legislation that would provide $300 million to construct a facility to breed and sterilize flies, but the House has left Washington for the summer.
Cattle farmers are urging Texas lawmakers, who on Monday gaveled in a 30-day special legislative session, to share the cost of a fly factory in Texas, instead of waiting for the federal government.
In economic terms, the screwworm is already here, modestly at least. About three percent of U.S. cattle come from Mexico, but citing inadequate surveillance of screwworm, the Agriculture Department cut off imports of Mexican cattle in November. Federal officials resumed the trade in February after Mexico put in place more rigorous inspection protocols. But imports were shut off again in May after the pest was detected in Veracruz and Oaxaca.
Even before the fear of pestilence, the industry was facing challenges. Drought and high feed prices have pushed the American cattle inventory to the lowest it has been since 1952, according to the Agriculture Department. Domestic beef prices hit record highs in May, at an average of $5.98 per pound for ground beef, according to the Bureau of Labor Statistics. Beef from Brazil, the world’s largest beef exporter, could bring some price relief, though President Trump has promised to impose a 50-percent tariff on Brazilian imports, beginning in August.
