New World Screwworm Infestations: Understanding the Threat and Response

The New World screwworm (*Cochliomyia hominivorax*) is a parasitic fly larva that causes myiasis, a condition where maggots infest the living tissue of mammals, including livestock, pets, and humans. While the United States eradicated the pest in 1982 through the Sterile Insect Technique, sporadic reintroductions occur, requiring rigorous surveillance by the U.S. Department of Agriculture (USDA) and state veterinary authorities to prevent widespread outbreaks.

How do screwworm infestations affect animals?

The adult female screwworm fly lays eggs near open wounds or mucous membranes on a host animal. Within 24 hours, these eggs hatch into larvae that burrow into the host’s living flesh to feed, creating deep, pocket-like wounds. According to the [USDA Animal and Plant Health Inspection Service (APHIS)](https://www.aphis.usda.gov/livestock-poultry-disease/cattle/screwworm), these infestations are painful and can be fatal if left untreated, as the wounds attract more flies and are highly susceptible to secondary bacterial infections. Unlike common blowfly maggots that feed on dead tissue, screwworm larvae exclusively consume healthy, living tissue.

Why are officials concerned about recent reports?

While the United States remains largely free of established screwworm populations, recent activity in neighboring regions has heightened biosecurity measures. The [Centers for Disease Control and Prevention (CDC)](https://www.cdc.gov/parasites/myiasis/index.html) classifies the New World screwworm as a reportable disease, meaning veterinarians must notify state or federal authorities immediately upon diagnosis. The concern stems from the potential for the parasite to establish a foothold in southern states, particularly in regions with high concentrations of livestock. Federal response strategies involve increased inspections of animals entering the U.S. and the deployment of sterile flies to disrupt the reproductive cycle of any localized populations.

What are the primary symptoms of an infestation?

Owners should monitor pets and livestock for specific signs of myiasis. The [American Veterinary Medical Association (AVMA)](https://www.avma.org/resources-tools/pet-owners/petcare/myiasis) notes that the most common indicators include:

• Persistent, non-healing wounds that appear to be deepening.
• Visible larvae within a wound, which may be mistaken for common maggots.
• Foul-smelling discharge from an open sore or body orifice.
• Animals showing signs of extreme irritation, biting at, or scratching a specific area of the body.
• Lethargy or a sudden drop in appetite.

How is a screwworm infection treated?

Treatment requires professional veterinary intervention to ensure the complete removal of all larvae. Veterinarians typically use specialized antiparasitic medications, such as doramectin or ivermectin, to kill the larvae, followed by the physical cleaning and debridement of the wound. According to the [FDA](https://www.fda.gov/animal-veterinary/animal-health-literacy/get-facts-about-screwworm), early detection is the most significant factor in a successful recovery. Owners should never attempt to treat suspected screwworm cases with home remedies, as improper removal can leave larvae embedded in the tissue or cause further trauma to the animal.

Key Takeaways for Pet and Livestock Owners

• Report Suspicions: If you find maggots in a living animal, contact your veterinarian or state animal health official immediately.
• Maintain Wound Care: Keep all animal wounds clean and protected from flies until they are fully healed.
• Travel Awareness: Be cautious when transporting animals from regions known to have screwworm activity, as this is the most common path for reintroduction.
• Prevention: Use fly control measures in barns and kennels to reduce the population of adult flies.

The USDA continues to monitor international trade and movement to ensure the screwworm does not regain a permanent presence in North America. By maintaining strict surveillance and rapid reporting protocols, the veterinary community aims to contain individual cases before they evolve into broader environmental threats.