New World Screwworm: What Pet Owners Need to Know Before Traveling
- Dr. Vince Rozyczko
- Jul 31
- 4 min read
An important guide for pet owners on New World Screwworm, including how it spreads, warning signs, travel considerations, and the importance of year-round parasite prevention.
With summer travel season upon us, there is a developing risk in the United States that warrants the attention of pet owners, especially those who travel with their pets.
Recently, the states of Texas and New Mexico have reported the presence of New World Screwworm (NWS) in domestic animals. It is a parasitic fly that completes part of its life cycle by feeding on the flesh of warm-blooded animals and even people.
These flies are attracted to wounds and natural body openings such as the nose, eyes, ears, and mouth, where they lay their eggs. The eggs hatch into maggots (larvae) that feed on living tissue, creating painful, foul-smelling wounds that continue to worsen over time.
These are not the common flies that lay eggs on dead tissue or decaying animals. New World Screwworm flies specifically target living animals and do not possess the enzymes necessary to break down dead, decaying tissue.
Because of this, changes related to pain, disease, or aging may not be obvious until the condition has progressed.
Something as small as the site of a tick bite can be enough of a break in the skin's protective barrier to allow a severe and painful maggot infestation to occur.
Even small shifts can indicate underlying medical concerns. If you notice any changes, it is important to contact your veterinarian.
The importance of year-round tick prevention for pets cannot be overstated, now more than ever.
FDA-Authorized Treatment Options
Some encouraging news is that, as of June 2026, the U.S. Food and Drug Administration has issued Emergency Use Authorization (EUA) for the following products to treat Screwworm infestations in dogs and cats:
NexGard® (afoxolaner) chewable tablets for dogs
NexGard® COMBO (esafoxolaner, eprinomectin, praziquantel) topical for cats
Credelio™ (lotilaner) chewable tablets for dogs and puppies
Credelio™ CAT (lotilaner) chewable tablets for cats and kittens
These products are available by prescription through veterinarians in the United States, and the NexGard products are always kept in stock at Brookeside Veterinary Hospital.
We have long recommended year-round tick prevention to help protect pets and families from ticks and the diseases they carry. The re-emergence of New World Screwworm adds another important reason to stay current on preventive care, as it has the potential to affect pets, livestock, people, and ultimately our food supply.
If you have questions or would like to discuss the preventive medications listed above, please call Brookeside Veterinary Hospital at 734-761-7523.
A Brief History of New World Screwworm in the United States
Historically, many years of eradication efforts were required to eliminate New World Screwworm from the United States and other countries. One of the primary methods involved releasing large numbers of sterile male flies, which reduced successful breeding and dramatically lowered the number of viable Screwworm eggs.
These efforts were so successful that the USDA declared the United States free of indigenous Screwworm in 1966.
However, a significant outbreak in 1972 demonstrated that U.S. livestock remained vulnerable through both the natural flight of the flies and the movement of infested animals. Continued international cooperation eventually led to Nicaragua being declared Screwworm-free in October 1999, followed by neighboring countries to the north.
Travel Considerations
Screwworm infestations (the presence of maggots on or within the body) are not regularly seen in the United States today. However, cases have occurred in travelers returning from areas where the flies remain established.
If you travel to affected areas, have an open wound, and spend significant time outdoors, you may be at greater risk of infestation.
Even if you or your pets avoid becoming infected while traveling, there are additional regulations to consider when returning from areas under animal movement restrictions. Some regions are designated as an "Infested Zone" or "Adjacent Surveillance Zone," and additional documentation may now be required when crossing state lines or flying domestically with pets.
Signs to Watch For
Screwworm infestations can be difficult to recognize during the early stages.
Watch for:
Draining or enlarging wounds
Signs of pain or irritation
A foul odor coming from a wound
Creamy white eggs or larvae near the edges of wounds
How to Protect Yourself and Your Pets
In areas where New World Screwworm is present, you can reduce the risk of infestation by:
Keeping all wounds clean and covered, no matter how small.
Wearing loose-fitting long sleeves, pants, hats, and socks to reduce exposed skin.
Using an EPA-registered insect repellent.
Treating clothing and outdoor gear with products containing 0.5% permethrin.
Sleeping indoors or in screened rooms or tents whenever possible.
Michigan Reporting Requirements
In Michigan, Screwworm is an emergency reportable disease in all species.
If you suspect your animal may have signs of a Screwworm infestation, contact the Michigan Department of Agriculture and Rural Development (MDARD) immediately.
Daytime: 800-292-3939
After Hours: 517-373-0440
Key Takeaways
New World Screwworm has recently been reported in domestic animals in parts of Texas and New Mexico.
Unlike common maggots that feed on dead tissue, New World Screwworm larvae feed on living tissue, causing painful, worsening wounds.
Even a small wound, such as a tick bite, can become an entry point for infestation.
Year-round tick prevention is more important than ever to help protect your pets.
If you're traveling with pets, be aware of changing regulations for animals returning from affected areas.
If you have questions about travel or parasite prevention, call Brookeside Veterinary Hospital at 734-761-7523.
Helpful Resources
Michigan Department of Agriculture and Rural Development (MDARD)
Centers for Disease Control and Prevention (CDC)
We encourage you to save this information for future reference and share it with friends and family, especially anyone planning to travel with pets this summer and in the months ahead.
Dr. Vincent Rozyczko
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