New World Screwworm: What Beef Producers Need to Know

The New World Screwworm (NWS) is a deadly parasite that attacks warm-blooded animals, including cattle. Though eradicated from the U.S. in 1966, recent outbreaks in Central America and Mexico show it’s still a threat.¹ The current situation regarding NWS can change rapidly.

Why it matters now:

• NWS is regularly found in Cuba, Haiti, the Dominican Republic and South America with cases now spreading as far north as Mexico.¹
• The U.S. and Panama are maintaining a barrier zone in eastern Panama to stop its northward spread.²
• In 2023, an unprecedented number of NWS cases were reported in Panama, followed by confirmed cases in every Central American country and Mexico.²
• NWS can cause millions in production losses and is harmful to humans as well.²
• Prior to eradication, the pest cost the U.S. livestock industry over $100 million annually³, and reintroduction could lead to major economic and animal health impacts.⁴

What to watch for:

• Irritated behavior, head shaking or the smell of decay.
• Maggots in wounds and visible egg masses or larvae by day 3.⁴
• NWS maggots burrow into live tissue, causing severe pain, withdrawal and loss of appetite.⁴

If you suspect NWS:

• Report it immediately to a veterinarian, State Animal Health Official or the USDA.⁴

Quarantine risk:

• USDA response plans include quarantines and movement restrictions in affected areas.⁵
• Permits may be required to move livestock, with inspections for wounds and myiasis.⁵
• Control decisions will be based on science, spread risk and environmental factors.⁵

Bottom line:

Early detection and prevention are key. NWS poses a serious threat to livestock, wildlife and even people. Staying informed and reporting concerns helps protect U.S. cattle herds and ranching livelihoods.

For USDA updates regarding NWS, visit NCBA’s website for more information.