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Animal Drugs for New World Screwworm

New World screwworm (NWS), Cochliomyia hominivorax, is a parasitic fly that lays eggs in and on open wounds and mucous membranes of warm-blooded animals. NWS larvae (maggots) burrow into the flesh of these animals and eat healthy living tissue. This infestation with larvae is called myiasis. NWS can infest livestock, pets, wildlife, occasionally birds, and in rare cases, people. The damage caused by NWS in animals can be serious and is often deadly to the animal. For updates on NWS, visit: New World Screwworm.

The FDA’s Center for Veterinary Medicine (CVM) is working closely with the U.S. Department of Agriculture (USDA), the Environmental Protection Agency (EPA), other U.S. government departments and agencies, and state animal health officials to address the threat of NWS.

CVM is working with drug sponsors, federal and state partners, and international regulators to understand options for U.S. veterinarians to treat NWS effectively and safely. 

On New World Screwworm: Information for Veterinarians, CVM provides information to support veterinarians with the identification of FDA regulated products to prevent and treat NWS myiasis.

The agency has multiple regulatory pathways under which animal drugs for NWS can be reviewed. To learn more about FDA’s pathways, see: FDA Regulation of Animal Drugs.

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Frequently Asked Questions (FAQs)

  1. What role does the FDA’s Center for Veterinary Medicine play in the preparedness and response efforts for NWS?

    CVM’s role is to review data and information submitted by animal drug sponsors to support the safe and effective use of drugs to treat or prevent NWS myiasis in animals, including food-producing animals, companion animals, and wildlife.  

    CVM is working in collaboration with the USDA, which is spearheading the nationwide response to NWS, on developing prevention and treatment strategies for NWS myiasis in animals. Additionally, CVM is coordinating with the Environmental Protection Agency (EPA), which regulates subsets of certain over-the-counter topical antiparasitic products and insecticides as pesticides, to understand potential EPA-regulated products that may be part of a prevention and treatment strategy.

  2. What mechanisms are available to provide for the use of drugs to prevent or treat NWS myiasis in animals?  

    FDA approval, supplemental approval, conditional approval, extra-label use and emergency use authorization are all mechanisms by which animal drugs could be made available for use to prevent or treat NWS myiasis. The appropriate mechanism(s) for each drug depends on factors such as current U.S. approval status, which animal species the drug treats, and data and information submitted for FDA review by a sponsor. It is likely that multiple regulatory mechanisms will be needed to ensure that there are appropriate options available to meet the needs of veterinarians, animal producers and pet owners.

    For example, FDA approval or supplemental approval are typical mechanisms by which animal drugs can be reviewed and brought to market. However, the time needed for sponsors to generate the necessary data in support of drug applications, and for FDA to review these applications, may not be compatible with the urgent nature of the NWS public health threat. Therefore, these typical approval mechanisms alone may not meet all needs. For more detail regarding some of these mechanisms, see: FDA Regulation of Animal Drugs.

  3. How does the HHS emergency declaration help make animal drugs for NWS available?

    After determining that New World screwworm presents a significant potential for a public health emergency that could affect national security, the Secretary of HHS issued a declaration on August 18, 2025. The declaration allows FDA to authorize the emergency use of certain animal drugs for NWS myiasis. This provides FDA with an additional mechanism to make animal drugs available in a way that is tailored to the specific circumstances of NWS and that may be more flexible than standard approval pathways.

    Animal drug sponsors interested in pursuing an authorization for the emergency use of a drug for NWS should email AnimalDrugNWS@fda.hhs.gov. FDA will follow up with sponsors to obtain any additional information needed to assess whether the product is eligible for review under the emergency authorization pathway for NWS.

    Animal drugs may be legally used where they are approved, conditionally approved, indexed, authorized, or, under certain conditions, used in an extra-label manner. 

  4. Can FDA approved products be used extra-label for NWS myiasis?

    Veterinarians may prescribe the use of FDA-approved products for uses that are not on the label, in accordance with the existing regulations (21 CFR Part 530) with a valid veterinary/client/patient relationship.

    CVM encourages veterinarians to review existing regulations regarding the extra-label use of animal drugs. It is particularly important for food animal veterinarians to be aware of the additional requirements for extra-label use in food-producing animals including rules against extra-label use of drugs administered as medicated feed. A helpful reference tool is: The Ins and Outs of Extra-Label Drug Use in Animals: A Resource for Veterinarians.

    On New World Screwworm: Information for Veterinarians, CVM provides information to support veterinarians with the identification of FDA-approved animal drugs labeled for indications other than NWS myiasis that scientific literature indicates may be effective to prevent or treat NWS myiasis.

  5. What products may be approved or authorized by CVM for NWS in animals? 

    CVM is committed to ensuring that animal prevention and treatment options are available to protect the health and safety of livestock, pets, and humans; to ensuring that food from any treated animals will be safe for consumers; and to considering important short- and long-term goals – including continued effectiveness of and potential resistance to different treatment options.  

    CVM is open to considering therapeutics with scientific evidence indicating safety and effectiveness for the prevention and treatment of NWS myiasis.

    While we cannot discuss any drug product or application under consideration, CVM encourages animal drug sponsors to contact us about potential treatments, scientific research, and regulatory pathways. 

  6. What should I know about the use of animal drugs in cattle and wildlife feed to prevent or treat NWS myiasis?

    CVM has received multiple inquiries regarding whether a medicated feed is available for preventing or treating NWS myiasis in cattle or wildlife.  Currently, no medicated feeds have been approved for prevention or treatment of NWS myiasis for any species. No medicated feeds containing ivermectin or doramectin are approved for any indication for cattle or wildlife in the U.S.  

    Although ivermectin and doramectin have been administered orally in limited, specific circumstances by federal and state animal health officials as part of USDA parasite control programs like the one for cattle fever ticks, data on safety and effectiveness for NWS myiasis and for wider use is limited. Federal law does not permit the extralabel use of animal drugs in feed.

    CVM is interested in obtaining data and other information about the safety and effectiveness of medicated feeds for preventing and treating NWS myiasis, as well as other types of animal drug formulations that may address administration challenges faced by the livestock, poultry or wildlife sectors. We are working with federal and state officials to understand animal emergency medical countermeasure needs for potential response scenarios. We encourage animal drug sponsors to contact us to discuss potential animal drugs to prevent or treat NWS myiasis. 

    Animal producers should work closely with their veterinarians and state animal health officials when determining the best plan of care for their animals. Because of antiparasitic resistance concerns, if animal drugs are needed, they should be used judiciously to preserve their effectiveness. For animals raised for food production, it is essential that the meat, milk, and eggs from these animals entering the food supply do not contain unsafe drug residues. 
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Relevant FDA Resources and Regulations

Partner Resources on New World Screwworm
USDA

U.S. Centers for Disease Control and Prevention (CDC)

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