New World Screwworm

NWS, Cochliomyia hominivorax - a devastating parasitic fly

USDA Confirms Presence of New World Screwworm in the United States

Animal Health Officials Working Quickly to Protect U.S. Livestock and Wildlife

WASHINGTON, D.C., June 3, 2026—The U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed the detection of a New World screwworm (NWS) in a bovine in Zavala County, Texas. NWS is a serious pest that affects livestock, pets, wildlife, and less commonly, people and birds. NWS larvae (maggots) burrow into the flesh of living animals, causing serious damage to livestock and economic losses.

The affected animal is a 3-week-old calf and larvae were identified in its umbilical area. To date, there have been no further detections.

“All models showed New World Screwworm entering the country in 2025; however, thanks to the hard work across the entire Trump administration and our industry, state, and local partners, we were able to buy time for this moment. Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action,” said Dudley Hoskins, Under Secretary for Marketing and Regulatory Programs. “USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before, and we will do it again.”

USDA and Texas officials are taking immediate action to contain and eradicate NWS from the United States, following the strategies and actions outlined in the NWS Response Playbook (884.59 KB). This includes:

Forming a unified Incident Command Team with the Texas Animal Health Commission and deploying response personnel to the area;
Establishing a 20 km infested zone around the detection and implementing quarantines, movement controls, and surveillance in this area;
Expediting targeted release of sterile NWS flies (423.58 KB) by immediately deploying ground release chambers in the area, in addition to the 4 million sterile flies per week already being released aerially in the area;
Increasing trapping for NWS flies along the border and just outside of the dispersal area;
Implementing NWS surveillance and management strategies in wildlife; and
Conducting targeted outreach in the local area.

Read the Full Article on USDA Website Here . . .

USDA-FDA Screwworm Announcement Timeline

FDA Issues Emergency Use Authorization for Over-the-Counter Injectable Drug

to Prevent New World Screwworm in Cattle

CVM Updates

February 5, 2026

Today the U.S. Food and Drug Administration issued an Emergency Use Authorization (EUA) for Ivomec (ivermectin) injectable solution against New World screwworm (NWS). The agency has concluded that based on the scientific evidence available, it is reasonable to believe that Ivomec may be effective for the prevention of infestations caused by NWS larvae (myiasis) in cattle when administered within 24 hours of birth, at the time of castration, or when a wound appears, and the known and potential benefits of the product outweigh its known and potential risks.

Ivomec is not for use in female dairy cattle producing milk for human consumption and calves that will be processed for veal. The slaughter withdrawal period for cattle is 35 days.

This EUA will be effective until it is revoked or the HHS Secretary terminates the declaration that the potential public health emergency presented by NWS justifies the emergency use authorization of animal drugs for NWS.

Ivomec is available over the counter without a prescription. Producers are responsible for using Ivomec in accordance with the product labeling and fact sheet. To reduce the risk of antiparasitic resistance and preserve drug effectiveness against both NWS and other parasites, producers are encouraged to use antiparasitic drugs like Ivomec only when medically necessary and as part of a comprehensive parasite management strategy.

The FDA has previously approved Ivomec to treat and control other parasites in cattle, swine, reindeer and American bison.

Ivomec is sponsored by Boehringer Ingelheim Animal Health USA, Inc. based in Duluth, Georgia.

New World Screwworm

NWS, Cochliomyia hominivorax - a devastating parasitic fly

Domestic Readiness and Response Policy Initiative

The New World Screwworm (NWS, Cochliomyia hominivorax) is a devastating parasitic fly native to the Western Hemisphere. When NWS fly larvae (maggots) burrow into the flesh of a living warm-blooded animal, it lays eggs in the living tissue of fresh wounds. The larvae (maggots) feed on the host’s flesh, causing severe wounds and often death if untreated. NWS can infest livestock, pets, wildlife, occasionally birds, and in rare cases, people.

The pest was eradicated in the U.S. in the 1960s. Since then, it occasionally reemerges and has resurfaced in Central America and Mexico. They are controlled only through the release of sterile males, known as the sterile insect technique (SIT). This approach, along with regular active surveillance and livestock inspections, has proven highly successful.

As of May 2025, renewed attention to this parasite is crucial, as it may pose future risks to livestock and wildlife. This is a fast-moving issue, as we have seen the border close, then open, now closed again. With a reported case in Veracruz in Mexico, the screwworm is 370 miles south of the U.S./Mexico border (see map below). It will be very important for us in Arizona to track these developments.

Secretary of Agriculture Brooke Rollins has been transparent in the plans the Department has created to fight this pestilence. They are focusing on three strategies to strengthen our response:

Effective controls on the movement of animals
Strong surveillance systems and public outreach
The use of sterile insect technology and exploring additional innovative methods of eradication.

Click this link to read and/or download the Domestic Readiness and Response Policy Initiative 5-Prong Strategy from USDA. This site will be updated as new information is available.