Should KY residents be concerned about New World screwworm detections in the US?

The U.S. Department of Agriculture announced on June 3 that the New World screwworm, a “serious pest” that affects livestock, pets and wildlife, has made its way to the United States

So far, the worm has been confirmed in Texas and New Mexico by the USDA. Kentucky Commissioner of Agriculture Jonathan Shell released a statement on June 10 emphasizing that no cases have been detected in Kentucky as of June 10, but the department is monitoring the situation.

Is the New World screwworm a threat?

Less commonly posing a threat to humans, the USDA said, the current risk to people in the United States is low. In animals, an infection can be fatal if left untreated.

Screwworm infestations occur when an adult female screwworm fly lays eggs in a wound or body opening causing larvae to hatch, burrow in the wound and feed on living tissue. Their feeding behavior is how they earned the name “screwworm,” the CDC said.

After approximately one week, the larvae detach from the host, turn into a pupa and go through metamorphosis. Depending on climate, after anywhere between seven and 54 days, the adult fly emerges.

Are screwworms contagious?

Screwworms can only spread through larvae infestation and are not contagious. They cannot spread from animal to human or human to human.

The USDA said screwworms cannot be transmitted through meat, poultry, fruits, vegetables or dairy products and are not a safety issue.

In Texas, the USDA confirmed that four cases of infected cattle and one case of an infected goat were across Gillespie, La Salle and Zavala counties. In New Mexico, one case of an infected dog was confirmed in Lea county.

Screwworms were deemed endemic in South America, parts of southern Central America and some Caribbean islands by the CDC, thriving in tropical and subtropical climates.

“Safeguards” were put in place in Mexico and the United States to ensure livestock do not carry screwworms across the border and patrol inspectors intercept and treat infected livestock if they do.

Watch for screwworm symptoms in animals

The USDA advises keeping an eye out for these symptoms in your livestock as a possible sign of screwworms:

• Smell of decay, foul odor
• Signs of pain such as irritated behavior, not eating, depression, or isolating themselves from other animals or people
• Maggots, white egg masses in wounds or body openings such as ears, genitalia, nose or the navel of newborn animals

How is New World screwworm treated?

Infested livestock are to be treated and quarantined until all wounds are healed and the animal has no evidence of reinfestation after 21 days, according to the USDA. Euthanasia will only be used in humane cases when treatment of the infestation is not feasible.

The Food and Drug Administration is currently working with animal drug sponsors to identify a possible drug to prevent or treat screwworms in livestock.

American Veterinary Medical Association livestock treatment steps:

• Remove all visible eggs and larvae in and around wound
• Provide wound care
• Prevent secondary infections
• Administer approved or otherwise authorized topical or antiparasitics through the bloodstream for affected species
• Reexamine animal after 24 hours and repeat treatment if live larvae persist

Next steps in Texas and Kentucky

The USDA said they are taking immediate action jointly with Texas officials to “contain and eradicate” screwworms using strategies previously outlined in a response playbook published in April 2026.

The USDA and Texas will do the following according to the playbook:

• Form unified Incident Command Team with Texas Animal Health Commission and deploy response personnel to infected area
• Establish 20 kilometer infested zone around detection and implement quarantines, movement controls, and surveillance in area
• Immediately deploy ground release chambers of sterile screwworm flies to expedite target release in addition to weekly 4 million screwworm flies released aerially
• Increase screwworm fly trapping just outside and along border of dispersal area
• Implement screwworm fly surveillance and management in wildlife
• Conduct targeted outreach in area

On June 5, the Kentucky Department of Agriculture issued guidelines of large animal movements from Texas to Kentucky to prevent the spread of screwworms to the Commonwealth.

• Any animal with clinical signs of screwworm infestation are prohibited from entering Kentucky. Large livestock originating from Texas must have a certificate of veterinary inspection 72 hours before entry, a Kentucky permit number and screwworm treatment notation.
• A signed statement saying livestock were free of screwworms by the Kentucky USDA Veterinary Services, Kentucky Office of Veterinary Services and a private Kentucky attending veterinarian is also required.
• If livestock from “Texas counties of concern,” are to be moved to Kentucky, they will require a special application alongside heightened requirements.

The guidelines are effective through Aug. 1 and may be amended after that date. Details are subject to change prior to Aug. 1.

Where did the screwworm come from? It is not new to the US

In 1933, the USDA said screwworms made their way to the Southeast United States within one year, ranchers reported cases in Alabama, Georgia, Florida, Mississippi, North Carolina and South Carolina.

The USDA’s 1931 annual report detailed the Entomology Research Branch conducting studies starting in 1929 regarding fly trapping as a way to reduce the number of screwworm cases in livestock.

Screwworms were eradicated in the Southeastern United States in 1959 through the sterile insect technique, which the International Atomic Energy Agency said is an environmentally-friendly sterilization technique using radiation on the insect’s reproductive cells.

The Southwestern United States followed suit introducing eradication programs in 1962 and officially declaring the program a success in 1966.

Prior to eradication, livestock producers in the Southeast lost an estimated $10-20 million per year due to screwworm infestations, the USDA reported. Producers in the Southwest lost approximately $50-100 million per year. Texas livestock producers were still sustaining approximately $132.1 million in losses each year due to screwworm infestations in the 1970s.

Livestock producers garnered $796 million per year in benefits from the 1990s through 2016, the USDA reported, as a result of eradication programs.