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Dear Veterinarian Letter: Use of FDA-Authorized Animal Drugs Against New World Screwworm Myiasis

June 5, 2026

Dear Veterinarian,

FDA’s Center for Veterinary Medicine is writing to follow up USDA’s announcement that New World screwworm (NWS), Cochliomyia hominivorax, has been detected in Texas near the U.S.-Mexico border.

This letter is intended to share resources to help you identify FDA-authorized or conditionally approved drugs for NWS myiasis and to explain veterinarians’ responsibilities when prescribing drugs with Emergency Use Authorizations (EUAs) for the prevention and/or treatment of NWS myiasis. FDA has been diligently working to prepare for NWS, including by issuing EUAs for animal drugs for the first time. We appreciate this is uncharted territory for you, and CVM stands ready to help veterinarians.

FDA-Authorized Drugs for NWS Myiasis

FDA has authorized several prescription and over-the-counter (OTC) animal drugs to treat and/or prevent NWS myiasis through two regulatory pathways: Conditional Approval and Emergency Use Authorization (EUA). Currently, no animal drug has received full FDA approval for NWS myiasis. Before issuing each EUA or conditional approval, FDA carefully reviewed data regarding animal safety, effectiveness, and in the case of food-producing animal species, human food safety, for each product.  

As of the date of this letter, the FDA has issued three conditional approvals and nine EUAs for animal drugs for NWS myiasis. We expect this count to grow as we receive and review additional drug applications and EUA requests.

For an up-to-date list of all FDA-authorized products for NWS myiasis, including links to Fact Sheets, Letters of Authorization (LOAs), and Freedom of Information (FOI) Summaries, visit: New World Screwworm: Information for Veterinarians.

Important Information for Veterinarians Using EUA Products

Veterinarians prescribing EUA products must inform clients that the products are authorized for emergency use but are not FDA-approved for the treatment or prevention of NWS myiasis. You are responsible for discussing the potential risks and benefits of EUA drugs with your clients, as well as any available alternatives. For food-producing animals, you must also make clients aware of any applicable withdrawal times specified in a product's LOA.

Veterinary facilities using or dispensing EUA products must maintain records that include client and patient information (name, age, disease manifestation); product information (number of doses administered or prescribed, lot number, and co-administered drugs); and the specific EUA condition for which the product is used. Please refer to each product's LOA for specific recordkeeping requirements.

Veterinarians should carefully review the labeling and use these products as indicated in the EUA or conditional approval. Veterinarians should carefully select products to match an animal’s clinical needs.  

Using FDA Authorized NWS Products and Reducing the Risk of Antiparasitic Resistance

Some countries dealing with NWS have seen antiparasitic resistance in NWS develop over time.  To ensure antiparasitic animal drugs continue to work when we need them most, FDA urges veterinarians to use FDA-authorized or conditionally approved products as indicated and only when medically necessary. Misuse, overuse, and use of drugs that have not been authorized or conditionally approved by the FDA could jeopardize the future effectiveness of antiparasitic drugs against NWS and other parasites. Products without conditional approval or an EUA for NWS have not been reviewed by FDA to verify their safety or effectiveness. Use of these products could also result in drug residues in the meat or milk of food-producing animals, which creates food safety concerns.

Extralabel Drug Use

Veterinarians may prescribe FDA-approved products for uses that are not on the label, in accordance with the existing regulations (21 CFR Part 530) in a valid veterinarian/client/patient relationship. CVM encourages veterinarians to review these regulations.

Food animal veterinarians should pay special attention to the additional requirements for extralabel use in food-producing animals, including rules against extralabel use of drugs administered as medicated feed.

Extralabel use of drugs in animals is limited to drugs with a full FDA approval, which means it does not include conditional approvals, index listed products, or products with an emergency use authorization (EUA). A small number of animal drugs have full FDA approval for non-NWS indications and conditional approval or an EUA for NWS myiasis. These animal drugs can be used in an extralabel manner because they have a full approval.

Adverse Event Reporting

FDA encourages veterinarians to report adverse events, including lack of effectiveness, associated with the use of any NWS-authorized product. Adverse events may be reported to the product's sponsor (contact information is available in a product's Fact Sheet or LOA) and/or to FDA directly (see How to Report Animal Drug and Device Side Effects and Product Problems). Reporting adverse events helps animal drug sponsors and FDA monitor product safety and effectiveness in real-world use.

If you have questions about FDA-authorized products for NWS myiasis, please contact FDA's Center for Veterinary Medicine at AskCVM@fda.hhs.gov. The FDA encourages veterinarians to contact their state veterinarian for region-specific risk information and recommendations.

Sincerely,

FDA’s Center for Veterinary Medicine

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