New World Screwworm: Information for Livestock & Animal Owners

In early June, USDA APHIS announced the detection of New World Screwworm in a 3-week-old calf in Zavala County, Texas. Additional cases have since been identified. View the USDA APHIS case dashboard.

What is New World Screwworm?

New World screwworm (NWS) is a type of parasitic fly that lays its eggs in open wounds or body openings (eyes, nose, mouth, etc.) of warm-blooded animals, including livestock, pets, wildlife, occasionally birds, and in rare cases, people.

When the eggs hatch, the larvae (maggots) burrow into the flesh like screws, hence the name, and feed on living tissue. This causes painful, dangerous infections called myiasis. NWS may be fatal if left untreated.

What to Look For

While these cases should not cause undue alarm in Oregon, animal owners and veterinarians should always watch for signs of any illness in their animals. 

Signs of NWS:

• Maggots or white egg masses in wounds or body openings, such as the nose, ears, genitalia, or the navel of newborn animals
• Foul odor or the smell of decay
• Signs of pain including irritated behavior, depression, not eating, and animals isolating themselves from other animals or people
• The flies are the size of a typical house fly with orange eyes and green iridescent bodies.
• Wounds as small as a tick bite can be infested with NWS.Treat for ticks and keep pets on flea/tick preventives year round to avoid open wounds.
• View USDA's New World screwworm photo gallery for images of flies, maggots, and infested wounds.

Prevention for Livestock Owners

• Wound prevention: Delay dehorning, branding, castration, shearing, and vaccination until after fly season.
• Inspect pens for sharp objects.
• Treat for ticks.
• Treat wounds promptly, including the umbilical stump of young animals. Use fly spray and bandage when possible.
• Closely monitor the herd for wounds around face and genitals.
• Check your vehicle for screwworm flies if you are in an NWS-infested area.

What to Do if You Suspect NWS

Immediately report any suspicious wounds, maggots, or infestations to your local veterinarian or the Oregon State Veterinarian’s office at 503-986-4711. Animals infested with NWS, myiasis, or a secondary infection should be immediately treated by a veterinarian.

ODA Rules

The Oregon Department of Agriculture (ODA) published final rules restricting the movement of animals from any area that is actively infested with New World Screwworm, and requiring enhanced inspection and preventative treatments prior to entry into Oregon. These requirements are in alignment with the USDA’s New World Screwworm Playbook, and include:

• All animals must be inspected by a veterinarian and obtain a Certificate of Veterinary Inspection within 5 days prior to departing an area infested with New World Screwworm.
• All animals departing an area infested with New World Screwworm must be treated with an accepted NWS treatment between 1 and 14 days prior to departure.
• Veterinarians must obtain an import permit at least 48 hours prior to animals departing an area infested with New World Screwworm.

For NWS resources and more information, visit ODA’s New World Screwworm page. If you suspect an infestation of NWS in your animal, immediately contact your local veterinarian or call the ODA Disease Reporting Hotline at: 503-986-4711.

Source: Oregon Department of Agriculture