New World Screwworm: Symptoms, Treatment & Prevention Guide

📌 New World Screwworm Kwik Summary

New World Screwworm (NWS) is a serious parasitic infestation caused by the fly Cochliomyia hominivorax. The screwworm parasite can affect a wide range of animals, including livestock, pets, wildlife, birds, and, in rare cases, people. Left untreated, a screwworm infestation can cause rapidly progressing tissue damage that may become fatal. Pet owners and animal caretakers should therefore understand the warning signs, treatment options, and prevention strategies. Early detection and proper wound management play a critical role in protecting animals from this destructive parasite.

In 2026, the New World screwworm was detected in Texas, raising concerns among veterinarians, livestock owners, and pet owners after decades of successful eradication efforts in the United States.

New World Screwworm Statistics (01/ 2024 to May 16/ 2026)

What Is a New World Screwworm?

The New World screwworm (Cochliomyia hominivorax) is a parasitic fly species that deposits eggs in open wounds and mucous membranes of warm-blooded animals. Unlike other flies that feed on dead tissue, the New World screwworm fly specifically targets healthy living tissue. 

The screwworm parasite spreads when a female fly is attracted to the smell of a wound or body opening - including the nose, mouth, eyes, ears, or genitals. Even something as small as a tick bite can attract egg-laying flies.

A single female can lay 200-300 eggs at a time, and up to 3,000 eggs over her 10 to 30-day lifespan. Those eggs hatch into maggots that immediately begin feeding on living tissue. After roughly 7 days of feeding, the larvae drop to the ground, burrow into the soil, and eventually emerge as adult flies ready to repeat the cycle.

Symptoms of a Screwworm Infestation

Early detection of New World Screwworm (NWS) infestations can save your animal's life. Symptoms of New World Screwworm (NWS) myiasis include visible larvae in wounds or body openings, such as the nose, ears, genital area, or umbilical region, along with egg masses in or around wounds. Infected wounds may produce a bloody discharge with a foul odor and can enlarge or deepen over time if left untreated. Affected animals may also show signs of irritation, including frequent head shaking or rubbing against objects. As the infestation progresses, they may experience pain, leading to depression, irritability, reduced appetite, or isolation from people and other animals. Early recognition of these symptoms and prompt veterinary care are essential to prevent severe complications.

Which Animals Are Most at Risk?

> New World Screwworm can affect any warm-blooded animal:

• Dogs and cats (especially those with untreated wounds).
• Horses and livestock (cattle, sheep, goats).
• Wildlife and birds.

Note : Any animal with an untreated wound is vulnerable. Even small injuries like tick bites can attract egg-laying flies.

Lifecycle: How screwworms spread

The life cycle of Cochliomyia hominivorax (New World Screwworm) takes about 21 days under favorable conditions. Adult flies mate, and the female lays hundreds of eggs in an animal's open wound. The eggs hatch into larvae that feed on living tissue and develop through three larval stages (L1-L3). After feeding for some days, mature larvae leave the wound, drop to the ground, and burrow into the soil. There, they enter the pupal stage and develop into adult flies over the next few days. Once the adult flies emerge, the cycle begins again.

New World Screwworm Lifecycle Stages

Treatment Options for Screwworm Infestation

• Veterinary Examination

A veterinarian will assess the extent of the infestation, identify affected tissue, and determine the most appropriate treatment plan. 

• Larvae Removal

Physical removal of all larvae is a critical part of treatment. Because larvae can burrow deep into tissue, professional removal is often necessary to ensure none remain behind.

• Wound Management

After larvae are removed, the wound must be cleaned and treated to promote healing and reduce the risk of secondary infections. Proper wound management remains one of the most important aspects of recovery.

• Fly Control

Preventing additional flies from reaching the wound is essential. Fly control measures or cleaning areas with veterinary-approved disinfectants help reduce the risk of reinfestation during the healing process.

Suspected Screwworm Cases Should Be Reported Immediately

If you suspect a New World screwworm (NWS) infestation, contact your veterinarian immediately. In the United States, suspected cases should also be reported to USDA-APHIS and state animal health officials as quickly as possible.

FDA-Authorized Treatment and Prevention Option

The U.S. Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) for F10 Antiseptic Wound Spray with Insecticide, which contains benzalkonium chloride, polyhexanide, and cypermethrin topical solution. 

According to the FDA, F10 Antiseptic Wound Spray with Insecticide may be effective for the prevention and treatment of New World Screwworm myiasis in specific animal species under the Emergency Use Authorization (EUA).

Important : F10 Antiseptic Wound Spray with Insecticide is not authorized for use in domestic dogs or cats under the FDA Emergency Use Authorization. Pet owners should consult their veterinarian for appropriate treatment options.

How to Prevent New World Screwworm Infestations

Prevention is far easier than treating an established infestation. Effective prevention focuses on wound management and livestock parasite control.

• Inspect Wounds Regularly

Check your pet or animal frequently for cuts, abrasions, scratches, surgical incisions, and skin irritations. Early identification of wounds allows treatment before flies have an opportunity to lay eggs.

• Clean Wounds Promptly

Even minor injuries should be cleaned and monitored carefully. Prompt wound management reduces the likelihood of attracting flies and lowers the risk of infestation.

• Monitor Surgical Sites

Animals recovering from surgery require close observation. Surgical incisions are considered high-risk wound sites because they can attract flies if not properly protected and monitored.

• Watch Tick Bites 

Tick bites, insect bites, hot spots, and small skin injuries may seem minor, but can create opportunities for flies to lay eggs. Inspect these areas regularly, especially during warm weather.

Conclusion

New World screwworm is a serious condition that requires prompt attention. Protection requires vigilance: regular wound inspection, prompt wound care, consistent fly control, and immediate veterinary attention at the first sign of trouble. By understanding the risks and implementing preventive measures, you can safeguard your animals from this dangerous parasite. Early detection and professional treatment remain your best defense against screwworm infestation.