For U.S. livestock producers facing New World screwworm, the treatment and prevention toolbox is limited but defined. There is no silver-bullet label today — because, legally, it doesn’t exist.
According to Brian Lubbers, veterinarian and board‑certified clinical pharmacologist, “There are no products currently that have full approval” for screwworm in cattle. That reality forces veterinarians and livestock owners to navigate a tightly regulated toolbox built on conditionally approved drugs and emergency use authorizations, all of which must be used exactly as labeled and under veterinary supervision.
“Extra label drug use only applies if a drug has full approval,” Lubbers explains.
Because all current NWS options in cattle are conditionally approved or under emergency use authorization, they cannot be legally used outside their specific labeled directions, including route, dose and species. That makes veterinary guidance and strict label adherence central to any treatment plan.
Blanket use may do more harm than good in the fight against NWS. As the number of NWS confirmations increases, so does the temptation to “stay ahead of it” with mass treatments. That approach worries veterinarians and entomologists.
“Anytime we use these products, whether it’s an antimicrobial or anti‑parasitic, there are always concerns of resistance,” Lubbers stresses. Echoing that message is Cassandra Olds, Kansas State University Extension entomologist, who adds that in regions with long‑term NWS problems, “there are cases of resistance developing.” She urges producers to “make sure that we use our products as we need them” and “not prophylactically, because we’re scared about what might happen in 5 months from now.”
Current NWS Toolbox Is Small But Defined
For cattle, the NWS toolbox consists of two conditionally approved products for prevention and treatment and several emergency use authorization products, all requiring veterinary oversight.
“All of these product uses have to be authorized by a veterinarian, and so for specific product recommendations, you really need to consult with your veterinarian,” Lubbers stresses. “Making the correct diagnosis is going to be important for both correct identification of larvae and treatment recommendations. They [veterinarians] can help work through the specific regulations that apply, and the products that, in their experience, are the most effective.”
The U.S. Food and Drug Administration (FDA) provides information to support veterinarians with the identification of FDA-regulated products to prevent and/or treat NWS myiasis. This includes FDA-approved animal drugs labeled for indications other than NWS myiasis that may be effective in preventing or treating NWS myiasis.
“We are not using these products to necessarily control the spread, right? That’s what the sterile fly release programs are about,” Lubbers explains. “This is about managing individual cases, and so we want to make sure we’re using these products in a judicious and limited fashion. We’re not going to treat our way out of the spread of New World screwworm.”
What Insecticides and Pesticides Are Registered for Screwworm Control?
Lubbers drew a clear line between drugs and pesticides and noted that several pesticides are registered specifically for screwworm control: “There’s a distinction here — insecticides are regulated by a different pathway, they’re not FDA‑regulated, they’re EPA and USDA‑regulated. So there are several pesticides that are registered for the prevention or control of screwworm. Some of those are on‑animal use, and some of those are essentially premise-use products.”
A list of pesticides to potentially use against NWS.
Neogen recently announced FIFRA Section 2(ee) recommendations for the use of Prozap® Insectrin X Concentrate and Prozap® Screw Worm and Ear Tick Aerosol. These recommendations provide ranchers, livestock producers, and horse owners with an additional option to support fly management efforts.
In Texas, the Texas Department of Agriculture has approved Section 2(ee) recommendations for these products. Neogen is also making Section 2(ee) recommendations available in Florida, providing producers in both states with additional tools to incorporate into broader fly management programs.
FIFRA refers to the Federal Insecticide, Fungicide and Rodenticide Act. Users must be in possession of the applicable recommendation at the time of pesticide application and comply with all product label directions and applicable state requirements.
Dr. Kirk Ramsey, Neogen professional services veterinarian, framed the expanded recommendations as one part of a broader integrated fly-control strategy rather than a stand-alone fix, noting that producers continue to manage routine pressure from horn flies, stable flies, face flies, ticks, and lice even as NWS draws new attention.
What’s Moving Off the Shelves
On the ground in the first infested zone, demand has been immediate and steep. Speer Ag, the family-owned feed and ranch supply business in Uvalde, Texas, reports animal health product sales in its NWS-relevant aisle ran 300% to 400% above normal in the week following the first confirmed case — with roughly 70% of customer transactions including some form of screwworm prevention or treatment product.
Top sellers, according to Cline Speer, include permethrin-based aerosol wound sprays, injectable doramectin (Dectomax) and other macrocyclic lactone pour-ons, and Exzolt, the conditionally approved fluralaner pour-on. Wound-care supplies — sealants, antibiotic sprays, and antibiotics such as LA-200, LA-300, and Excede to manage secondary infection — are also moving quickly, since an open wound left untreated after fly larvae are removed can still threaten the animal.
Supply has tightened correspondingly. Name-brand products have gone on allocation in some cases, according to Speer, with distributors substituting comparable alternatives to keep shelves stocked. Speer says his suppliers have been responsive given the region’s status as ground zero for the outbreak, but he’s watching the situation closely as demand continues across cattle producers, hunting-ranch operators, and even pet owners concerned about backyard animals.
AABP Opposes Ivermectin in Feed, Backs Existing Regulatory Pathway
American Association of Bovine Practitioners (AABP) recently shared a letter regarding NWS.
“AABP members will be on the front lines to address the recent incursion of New World Screwworm (NWS). Although many of the products that may be used to treat these infestations in cattle are over-the-counter, AABP encourages all producers to work with their veterinarian to develop identification, treatment and prevention protocols for their operations,” the letter says. “It is critical that veterinarians work with producers to ensure that animals are inspected daily to identify cattle infested with NWS. Identification of infected animals will allow for individual animal treatment as well as reporting to state and federal animal health authorities so that prevention measures based on the USDA New World Screwworm Playbook can be implemented. Reporting affected premises will allow for sterile fly dispersals and other interventions to control the spread of NWS.”
Here are some key takeaways:
- AABP Does Not Support Authorizing the Use of Ivermectin in Feed or Other Products Meant to Be Consumed Free-Choice by Range Cattle
“Currently, AABP does not support the use of this delivery method,” the letter stresses. Concerns listed include:- Bioavailability and dosing
A core scientific objection is pharmacokinetic. The letter notes there is a dramatic reduction in bioavailability of ivermectin delivered orally versus injectable ivermectin. Beyond that, free-choice feeding compounds the variability problem: in-feed ivermectin available free choice will also result in increased systemic ivermectin concentration variability due to variation in both oral bioavailability and feed intake differences between individual animals. AABP warns this combination “may result in animals receiving a subtherapeutic dose, which can result in therapeutic failure.” - Resistance risk
AABP frames this as a parasitology issue with long-term consequences, noting there is an increasing resistance to anthelmintics in cattle generally. Specifically for NWS, the letter cautions that widespread ivermectin use may increase resistance pressure of parasites and the development of resistance to ivermectin for NWS, which could potentially select for cross-resistance to other NWS therapeutics — a risk AABP backs by referencing numerous studies demonstrating widespread ivermectin resistance in Central and South America. - Regulatory and surveillance concerns
AABP points out a legal gap: in-feed ivermectin does not currently have FDA authorization for this use, and extralabel drug use in feed is prohibited. There’s also a behavioral/epidemiological concern — free access to ivermectin on open range may create a false sense of security, resulting in underreporting of cases, undermining the individual-animal inspection and reporting system the USDA playbook relies on.
- Bioavailability and dosing
- AABP Supports the Existing Regulatory Pathway
The organization supports products that have been conditionally approved or are under emergency use authorization for NWS. - AABP Supports Continuing Research on Treatment Modalities
This includes research on the effectiveness and consequences of delivery of these medications through feed and other delivery methods.
What Does This Mean for Your Operation?
- Work with your veterinarian before treating. Every currently available NWS product — conditionally approved or EUA — requires veterinary authorization, and dosing, frequency, or route outside the label isn’t permitted the way it would be for a fully approved drug.
- Inspect animals daily. Early identification allows individual treatment and is the basis for reporting to state and federal animal health authorities, which in turn triggers sterile fly dispersal and other containment measures in your area.
- Report suspected cases. NWS is a reportable disease; delaying identification doesn’t just risk the individual animal; it slows the broader containment response.
- Watch FDA’s website for product updates. Emergency use authorizations are tied to the federal emergency declaration — if conditions change, so could product availability under that pathway.
The spread of NWS this summer remains the central unknown. Warm, wet conditions across much of Texas this season are favorable for the fly, and absent a hard freeze, affected areas farther south may not see natural die-off at all. For now, the message from veterinary and regulatory experts alike is consistent: Use what’s approved, use it as labeled, inspect early and report fast.
