Three new cases of New World screwworm have been confirmed in the U.S., with one appearing outside the main cluster in Texas.
Officials say the spread is making people worry about how hard it could be to get the parasite under control so that it wouldn’t affect the cattle industry.
What is Screwworm?
Despite its name, screwworm isn’t a worm at all – it’s actually the larval stage of a fly.
Unlike typical maggots that feed on dead matter, these larvae invade living tissue.
The adult flies lay eggs in open wounds on animals like cattle, and in some cases, can also affect wildlife, pets, and even humans.
So far, there are five confirmed screwworm infections in total.
Four of the cases are in Texas and involve three calves and a goat, while the fifth case involves a dog in New Mexico. The dog was first reported as a Texas case but officials later confirmed that it actually lives in New Mexico.
Since the dog hadn’t recently been in Texas or Mexico, investigators are now focusing on its local surroundings to figure out where the infection came from.
The earliest cases were found in two calves in South Texas, just a short distance apart. More recently, two additional infections were reported; one involved a calf in La Salle County while one involved a goat in Gillespie County.
In attempts to slow things down, officials have set up quarantine zones of about 12 miles around each confirmed location.
While cattle are the main concern, experts warn that wildlife could also be affected.
Texas, in particular, has large populations of white-tailed deer, and a wider outbreak could potentially cause serious harm to them as well.
Researchers believe more cases might show up soon, however, they emphasized that that doesn’t automatically mean the worm is spreading at a quick pace.
The screwworm gets its name from the way the larvae burrow deep into wounds as they feed. Left untreated, infections can become severe and even fatal within weeks.
The good news is that there are approved treatments available for livestock.
Federal agencies and the cattle industry have been on alert since the parasite first reappeared in Mexico in late 2024.
One key strategy being used is the release of sterile male flies, since female flies usually mate only once; pairing them with sterile males will help stops reproduction.
In fact, officials have already been releasing sterile flies in South Texas since February.
They also plan on boosing production capacity by building a new facility in Texas.
Other countries are reacting as well, with Canada temporarily pausing imports of cattle, horses, and other livestock from Texas.
Since the flies prefer warm and humid conditions, experts expect the risk to rise as temperatures increase in the summer.
According to scientists, the sterile fly program is still the most effective long-term solution, though it may take some time before it fully works. The idea is to release enough sterile males so that the population collapses.
In the meantime, Texas officials are urging ranchers to keep a close watch on livestock and wildlife.
They’ve also rolled out a hotline and tracking tools so suspected cases can be reported quickly.
