The FDA has authorized a wound spray to prevent New World screwworm infestations in sheep, cattle, goats, swine, and camelids, along with several captive and captured wildlife species, including cervids, American bison, bighorn sheep, and Sonoran pronghorn.
CLiK Extra, a dicyclanil topical suspension sponsored by Elanco, received an emergency use authorization on Aug. 7. The authorization covers application on or around wounds, including those associated with birth and following surgical procedures.
One limitation is stated explicitly: the product prevents infestations. Elanco notes that if a wound is already infested, or an infestation develops after application, alternative treatment is necessary.
The Biology That Makes This Parasite Different
Most fly larvae found in animals feed on dead tissue. Cochliomyia hominivorax does not.
The female fly is drawn to open wounds, including cuts, tick bites, navels of newborn animals and surgical sites, where she lays a batch of eggs at the wound margin. The larvae that hatch burrow into living tissue and feed on it, screwing deeper as they grow, which is the origin of the name.
That behavior creates a compounding problem. The wound enlarges and produces an odor that attracts additional female flies, so a single small injury can accumulate successive waves of infestation. Untreated animals can die within one to two weeks.
The parasite was eradicated from the United States decades ago through sterile insect release, in which sterilized male flies are released in numbers sufficient to outcompete wild males. Its northward movement and the USDA's confirmation of a case in a three-week-old calf in Zavala County, Texas, are the reason the emergency authorizations exist.
"The FDA recognizes that the impact of New World screwworm extends beyond the farm gate," said Timothy Schell, director of the FDA's Center for Veterinary Medicine. The agency concluded that based on the totality of available scientific evidence, it is reasonable to believe the product may be effective when used as authorized and that the known and potential benefits outweigh the risks.
Livestock as the Front Line
Cattle and other livestock carry the practical burden for reasons that have little to do with susceptibility.
Herd animals accumulate wounds constantly, through routine husbandry procedures, fencing, insect bites, and birth. They are numerous, they are outdoors, and they are difficult to inspect individually at the frequency the parasite requires.
That combination makes livestock both the population most at risk and the population whose protection determines whether the fly establishes itself. A screwworm population that cannot find hosts cannot sustain itself, which is why Elanco's technical guidance emphasizes vigilance and early intervention as the way to minimize animal injury and limit spread.
CLiK Extra will be available through standard product channels to animal health professionals, livestock producers, and those managing captive and captured wildlife. The FDA's fact sheet accompanying the authorization contains product information including important food safety information, which producers and veterinarians should review before use.
The Sequence of Authorizations Behind It
CLiK Extra is the latest in a series rather than a standalone action. The HHS Secretary declared in August 2025 that circumstances justified emergency authorization of animal drugs against screwworm, and the FDA has issued authorizations steadily since.
According to the agency's running list, an ointment for multiple species was authorized on April 24, a topical powder on April 27, an over-the-counter injectable covering dairy cattle, horses, swine, sheep and deer on May 19, a generic over-the-counter treatment for dogs and cats on June 11, and a short-term preventive for horses on July 15.
That sequence matters for interpreting the news. Each product fills a different gap: some prevent, some treat, some cover species others do not, and some are available over the counter while others are not. The emergency pathway allows products not otherwise approved in the United States to be deployed quickly, which is why the list has grown.
The authorization remains effective until it is revoked or the HHS Secretary terminates the underlying declaration.
The Rare Route to Human Infection
Human cases occur, and they are uncommon enough that most clinicians will never see one.
The mechanism is identical to that in animals. A fly deposits eggs at an open wound, and larvae invade living tissue. Human infestation, called myiasis, therefore requires an existing wound or an accessible mucous membrane rather than intact skin.
The people at elevated risk are those with untreated open wounds who sleep outdoors or have limited access to wound care, along with travelers to areas with active transmission who have open sores. Cases have also involved the nose, mouth, ears and eyes, particularly in people who are unconscious, debilitated or unable to protect those areas.
Symptoms include a wound that will not heal, visible movement within the wound, a foul odor, discharge and pain that intensifies rather than settling. Treatment involves removal of larvae, wound cleaning, and management of secondary bacterial infection.
The practical guidance for people is unremarkable and effective: keep wounds clean and covered, seek care for wounds that are not healing, and use insect repellent in areas with active transmission. Anyone who has traveled to an affected region and develops a wound that seems to worsen, smells unusual, or appears to contain moving material should seek medical attention and mention the travel history, since clinicians unfamiliar with the parasite may not consider it.
Veterinarians who suspect screwworm should contact their state animal health official or the USDA rather than managing it independently. MedicalDaily has covered the agencies managing multiple concurrent outbreak responses and gaps in imported food oversight.
Key Questions Answered
What was authorized? CLiK Extra, a dicyclanil topical suspension wound spray, for prevention of New World screwworm infestations in sheep, cattle, goats, swine, camelids and several captive and captured wildlife species, under an emergency use authorization issued Aug. 7.
Does it treat existing infestations? No. It has not been shown to treat active infestations. If a wound is already infested, alternative treatment is necessary.
What makes screwworm different from other fly larvae? Most fly larvae feed on dead tissue. Screwworm larvae burrow into and feed on living tissue, enlarging the wound and attracting additional flies. Untreated animals can die within one to two weeks.
How does it reach humans? Through the same mechanism: a fly deposits eggs at an open wound or accessible mucous membrane. It cannot penetrate intact skin. Human cases are uncommon.
Who faces the most human risk? People with untreated open wounds who sleep outdoors or lack wound care access, travelers to areas with active transmission who have open sores, and people unable to protect the nose, mouth, ears or eyes.
What symptoms should prompt care? A wound that will not heal, visible movement within it, foul odor, discharge, and worsening pain. Mention any travel to affected regions, since unfamiliar clinicians may not consider the diagnosis.
Is this the only authorized product? No. It joins a series of emergency authorizations issued since 2025, including an ointment, a topical powder, injectables, and treatments for horses, dogs, and cats.
