Flesh-eating cattle parasite screwworm spreading in US
Two more cases of New World screwworm, hundreds of miles apart, have been confirmed in Texas, the U.S. Department of Agriculture said, illustrating the difficulty of stopping the spread of a pest that could potentially devastate the U.S. cattle industry.
The screwworm is a fly larva that eats live flesh rather than dead material.
Females lay their eggs in the open wounds of warm-blooded animals such as cattle, but wildlife, pets, and sometimes even humans can become infested.
A government program to breed sterile male flies and release swarms of them from airplanes to mate with wild females had kept screwworms in check at the southern tip of Panama for decades.
There are four confirmed cases in Texas so far.
The latest involved a calf and a dog in La Salle and Andrews counties, respectively, the USDA said.
The first cases of screwworm were discovered last week in two calves within a few miles of each other in South Texas.
Edward Burgess, a University of Florida entomologist who studies the fly, said scientists expect a handful of new cases to emerge in the coming days and weeks, but that doesn’t mean the screwworm is spreading rapidly.
“When the first case is seen, everyone is on guard and all eyes are on them more intensely,” Burgess said.
“And when you’re looking for something, you’re more likely to see it.”
In a statement made on Monday, the agriculture ministry said that officials took samples from suspicious cases and were working to completely eliminate the pest.
The USDA and the U.S. cattle industry have been racing to prevent the infestation since screwworm was detected in Mexico in late 2024.
Before screwworm was eradicated from the United States in the 1960s, it was an annual scourge of cattle farmers during warm weather.
So far its reemergence hasn’t greatly affected beef prices, which were already near record levels because there are fewer cows in the United States.
Although the parasite attacks live cattle, it does not infect meat or fruit.
There are also a dozen drugs approved by the government to treat farm animals.
Canada temporarily halted imports of cattle, horses and other livestock from Texas on Friday.
The parasites prefer humid areas where the temperature is 25°C, making them more of a problem in the summer months in the north.
The long-term solution — breeding sterile male flies — is months away, Burgess said.
Because wild female flies mate only once, if that encounter occurs with a sterile male, outbreaks can eventually be stopped as the flies die.
USDA is working to both increase sterile fly production at facilities outside the United States and build a massive fly factory in Texas.
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