New World Screwworm (NWS) is an infestation of individual animals, not a herdwide infection like many diseases. Finding one infested animal does not automatically mean the whole herd is infested.
“This is not infection,” explains Adis Dijab, DVM and veterinary services associate deputy administrator for USDA’s Animal and Plant Health Inspection Service (APHIS). “When you talk about infection, there is a potential that every single animal is infected. In this case, it’s [the] infestation of one animal; you can check the rest of your animals and they can be fine.”
What does this mean for operations? If NWS does cross the border, quarantine and movement controls will be designed to inspect and treat affected animals. Dijab says this means producers can clear the rest of the herd as quickly as possible, and there will be a pathway to continue business, not a blanket, long‑term stop on all movement — assuming cooperation and inspections.
APHIS will try to avoid blanket shutdowns by targeted zoning and quick pathways out of quarantine after inspection and treatment.
Dijab gave a NWS update during the cattle health and well-being committee at CattleCon. Here are four key points from his presentation:
1. What NWS is and why it’s dangerous
- NWS is a parasitic fly whose larvae require living tissue to feed.
- Its life cycle is 21 days but can be longer in colder climates.
- The fly is not active around 40°F.
- NWS flies prefer water, shade greenery and hosts.
- They typically move only about 3 km (approximately 1.6–1.7 miles) per day if they must; they are not strong long‑distance flyers.
Dijab shares the top 10 conditions leading to myiasis in Mexico, with umbilical being No. 1.
2. Current NWS Spread Pattern in Mexico Strongly Suggests Illegal Movement of Animals, Not Just Fly Movement
“One of the primary modes of movement of this fly is not flying of the fly; it’s a set of 18 wheels doing probably 60 or 70 [mph] down the road,” Dijab says. “Southern Veracruz had a pretty healthy number of the cases. Then suddenly it jumped into the middle of Tamaulipas, which clearly showed there was illegal movement.”
Due to this concern, USDA took the proactive action to start dispersing sterile flies in the southeast corner of Texas as well.
3. Sterile Insect Technique Is Key
- The U.S. has long relied on sterile insect release as its primary eradication tool.
- Panama facility (COPECA) currently produces approximately 100 million sterile pupae a week.
- “This is what’s keeping us alive right now,” Dijab says. “This is the reason that we don’t have a New World Screwworm on the U.S. soil.”
- A new U.S. facility is planned at Moore Air Base in South Texas. Dijab says the construction award is targeted for March/April, with an operational goal of 300-million sterile flies a week by 2027. He adds they expect a six-to-eight-month ramp‑up.
- The U.S. is collaborating with Mexico in remodeling a fruit-fly facility in Metapa, Chiapas. The U.S. is investing approximately $21 million. The goal is 100 million sterile flies a week, with first output expected late summer.
- The combined goal is approximately 500 million sterile flies a week, similar to volumes used in the 1990s’ eradication to the Darién Gap.
Dijab summarizes that APHIS is rebuilding and expanding sterile fly capacity to historical eradication levels, which is essential for long‑term regional control and eventual border reopening.
4. The U.S. is Using a Layered Defense: Strict Import Controls, Active Surveillance and Border Trapping to Detect Any Incursion Early
The two main surveillance streams are:
- The Foreign Animal Disease Diagnostician (FADD) network of 400 trained federal and state veterinarians.
- Trap lines along the U.S.-Mexico border, placed near water, livestock and greenery.
Dijab says that, since June, there have been more than 300 FAD NWS investigations, with zero findings so far and more than 900 hide/wildlife inspections. He adds that what scares him the most regarding NWS is wildlife.
Read More: The Importance of Wildlife Monitoring for New World Screwworm
