What is the New World Screwworm, and should you take precautions in Illinois?
The U.S. Department of Agriculture has reported 12 cases of New World Screwworm infestations in animals so far in June, and while it hasn’t yet been seen in Illinois, screening and monitoring is recommended.
The New World Screwworm, or NWS, is a parasitic fly whose larvae require living flesh to feed, according to the University of Illinois Urbana-Champaign extension office.
“While NWS is not in Illinois or our region, it would be worthwhile to inform yourself of what to look for and keep a heightened awareness of where NWS has been detected,” UIUC Extension Commercial Agriculture Educator and Beef Cattle Specialist W. Travis Meteer told the News-Democrat in a recent email.
The NWS was eradicated from the U.S. in 1966, but moved north from South America through every country in Central America and Mexico since 2023, according to the U.S. Centers for Disease Control and Prevention.
The USDA reports as of June 16 there were 11 active NWS cases in the U.S., as well as one inactive case. Eight active cases are in cattle, two are in goats and one is in a dog. The inactive case affected sheep.
Eleven of the 12 reported cases have been in Texas, and the other is in New Mexico.
NWS is not contagious like a virus, but instead spreads through flies that lay eggs in open wounds, Meteer wrote in a June 8 article.
What is a NWS infestation like?
Because NWS larvae eat living tissue, they can cause pain, enlarging wounds and secondary infections, according to Meteer. Animals that don’t receive treatment can die within one to two weeks.
All livestock, pets, horses, birds and wildlife can be at risk of NWS.
Humans can be infested with NWS, but it’s “very rare,” Meteer wrote.
“Infection would present as a painful wound that can be easily treated. The risk of death in humans is extremely low, especially if they seek treatment,” Meteer continued.
The adult NWS fly is the same size as a housefly but has a metallic blue and green body, and the larvae are a cream white maggot, according to Meteer. On an infected animal, you would see maggots inside wounds or wounds that get larger instead of healing.
Should you take precautions in Illinois?
The daily care of animals does not need to change at this point, Meteer said, but additional screening and monitoring is warranted.
“I think the greatest risk to Illinois would be that an animal would enter from an infected area,” Meteer said. “So, animals that are being transported into the state from the south and areas that are much closer to the confirmed cases should be screened and monitored closely.”
Meteer recommended speaking with your veterinarian if your animals will be traveling or coming from areas with reports of NWS.
The U.S. Food and Drug Administration recently issued an emergency use authorization for a generic over-the-counter drug, Nitenpyram tablets, to treat NWS infestations in dogs and cats at least four weeks old and weighing at least two pounds.
The risk of NWS coming to Illinois could increase, but USDA staff are working to stop it before it moves north, so the risk is currently low, Meteer wrote. The USDA uses a sterile insect technique to mitigate NWS populations. Some states, including Missouri and North Carolina, have instituted veterinary inspection requirements for animals entering the state that are coming from states with NWS infestations.
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