06/09/2026
If looking at these creepy vampire-looking things bothers you, imagine what they feel like literally chewing and worming their way into your pets' skin....
The U.S. Department of Agricultureās (USDA) Animal and Plant Health Inspection Service (APHIS), alongside State partners in Texas and New Mexico, continues to lead an aggressive response to New World screwworm (NWS) in the United States.
USDAās National Veterinary Services Laboratories has confirmed another new case of NWS in a calf in La Salle County, Texas, bringing the total cases of NWS in the United States to five. USDA is working closely with the Texas Animal Health Commission (TAHC) to respond and further investigate the case. The joint federalāstate field teams have already expanded surveillance and response measures in the area.
New World screwworm is a parasitic fly that causes severe, potentially fatal infestations by feeding on the living tissue of warm-blooded animals. Quick detection, treatment, and reporting are vital to safeguarding livestock, wildlife, and pets.
The name screwworm refers to the maggots' feeding behavior as they burrow (screw) into the wound, feeding as they go like a screw being driven into wood. Maggots cause extensive damage by tearing at the hostsā tissue with sharp mouth hooks. The wound can become larger and deepen as more maggots hatch and feed on living tissue. As a result, NWS can cause serious, often deadly damage to the animal.
Adult screwworm flies are about the size of a common housefly (or slightly larger). They have orange eyes, a metallic blue or green body, and three dark stripes along their backs.
Report mammals and birds with the following signs to your veterinarian:
⢠Irritated behavior
⢠Head shaking
⢠The smell of decay
⢠Presence of fly larvae (maggots) in wounds
USDA and TAHC are conducting a coordinated response that includes:
⢠Joint epidemiological investigations and case tracing
⢠Additional surveillance, testing, and trapping in the affected areas
⢠Releasing sterile insects and adjusting these operations as needed for the most effective coverage
⢠Conducting outreach to animal owners
⢠Ongoing coordination with local officials, veterinarians, ranchers, and community partners
Guidance for Animal Owners and Veterinarians:
The MOST important thing animal owners can do is to know what to look for and how to report suspected cases of NWS. USDA urges everyone in the area to check animals for:
⢠Draining or enlarging wounds
⢠Maggots or egg masses
⢠Signs of discomfort
⢠Lesions in body openings (nose, ears, genitalia, umbilical area)
Anyone who suspects a screwworm infestation should immediately contact their veterinarian, state animal health official, or USDA. Early reporting is essential to ensure animals receive prompt treatment, so they fully recover.
Though rare in people, anyone who notices a suspicious lesion should seek immediate medical care.
Treatment & Preventatives for Dog & Cat Owners:
The U.S. Food and Drug Administration has issued Emergency Use Authorizations (EUAs) for Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, pyrantel) chewable tablets, and NexGard (afoxolaner) chewable tablets for the treatment of New World screwworm (NWS) infestations (myiasis) in dogs.
They have also issued an EUA for NexGard COMBO (esafoxolaner, eprinomectin, and praziquantel topical solution) for the treatment of NWS myiasis in cats.
Credelio Quattro CA-1, NexGard and NexGard COMBO are available only by prescription from a licensed veterinarian because professional expertise is required to monitor for and respond to potential adverse reactions.
In addition to the EUA, Credelio Quattro CA-1 and NexGard chewable tablets are already FDA-approved for flea and tick-related indications in dogs and puppies. NexGard COMBO topical solution is already FDA-approved for flea, tick, and worm-related indications in cats and kittens.
Conditionally approved animal drugs have been shown to be safe and have a reasonable expectation of effectiveness, and the conditional approval is valid for one year, and the drug sponsor can ask FDA to renew the conditional approval annually for up to four more years, for a total of five years of conditional approval. Credelio Quattro-CA1 is sponsored by Elanco US Inc., and Nexgard and Nexgard Combo are sponsored by Boehringer Ingelheim Animal Health USA.
Calm Animal Care carries all three of these preventatives, and recommends that pet owners keep their dogs and cats on parasite preventatives year-long, due to the 4 million plus visitors that visit the Flathead Valley annually, that may or may not treat their own pets. Veterinary appointments are legally and medically required for most preventative care. The FDA and the state of Montana both mandate that Veterinarians must establish a valid Veterinary-Client-Patient Relationship, and an in-person annual exam to legally write or renew prescriptions, including preventatives.
Food Safety:
The U.S. food supply remains safe. NWS does not infest meat, fruits, vegetables, or other food products. Any affected animal would be identified during USDA Food Safety and Inspection Service inspection, and no contaminated product would enter commerce.
Travel Restrictions:
Both Canada and Mexico have placed restrictions on the export of live animals from the United States due to the New World Screwworm (NWS) detections, effective immediately. At this time, we do not know if Canada will add restrictions on animals from New Mexico in response to the announcement by the USDA of the detection of NWS in a dog located in Lea County, New Mexico. Affected species include dogs, cattle, equine, sheep & goats, swing, ferrets, and birds. Dogs entering the U.S. from Mexico still require screwworm inspection/certification. This is a constantly changing story, and updates will be posted regularly at screwworm.gov.