Screwworm: What Dog Owners Need to Know

New World screwworm is back in the news—and if you’re a dog owner, it’s completely reasonable to feel concerned. This parasite was eradicated from the United States decades ago, so recent reports can sound alarming at first.

But there’s an important detail that often gets overlooked: increased reporting is actually a sign that surveillance is working. As veterinarians, animal health officials, and pet owners become more aware of what to look for, more cases are being caught early.

Right now, the USDA is tracking confirmed cases and encouraging pet owners to watch for signs like unusual wounds, especially those that are bloody, foul-smelling, or contain visible larvae or eggs. As with any evolving situation, guidance will continue to be updated as experts learn more.

What is New World Screwworm?

New World screwworm is a parasitic fly whose larvae feed on living tissue. Unlike many other pests, this one doesn’t just target dead or decaying matter—it invades healthy skin.

Female flies lay eggs near small wounds or moist areas of the body, including the nose, ears, mouth, navel, or genitals. And it doesn’t take much—something as minor as a tick bite or small scratch can provide an entry point.

Once the eggs hatch (usually within 12 to 24 hours), the larvae begin burrowing into the tissue. This creates a painful wound that can quickly worsen if left untreated. In severe cases, it can become life-threatening.

Why is it reappearing?

The U.S. successfully eliminated screwworm through one of the most effective animal health programs in history. The strategy involved releasing sterile male flies into the wild. Since female flies only mate once, mating with a sterile male stopped reproduction and gradually wiped out the population.

By the early 2000s, screwworm had been pushed as far south as the Panama Canal. However, in recent years, it has started moving north again. Some of that spread is natural, while some is linked to the movement of infested animals across regions.

A key challenge today is infrastructure. Many of the facilities that once produced sterile flies were shut down after eradication. Rebuilding that capacity takes time, which means control—not immediate elimination—is the current focus.

Should dog owners worry?

Screwworm most commonly affects livestock, especially cattle, but it can infect a wide range of animals, including dogs and cats. A recent U.S. case involving a dog highlights why awareness matters.

That said, for most household pets, the overall risk remains relatively low.

Dogs at higher risk include those that are:

• Free-roaming or stray

• Recently rescued or transported

• More likely to have untreated wounds

For the average pet dog, simple habits make a big difference. Regularly checking your dog, keeping wounds clean, and contacting your veterinarian if something looks unusual are highly effective protections.

If you travel with your dog or participate in rescue or transport work, extra vigilance is important. The movement of animals has played a role in spreading the parasite in some areas.

Prevention and treatment

There are tools available to help protect pets. The FDA has issued Emergency Use Authorizations for certain products used to treat or help prevent screwworm infestations in animals, including dogs and cats.

Because recommendations may evolve, your veterinarian is the best source for up-to-date guidance.

In general, prevention comes down to reducing opportunities for flies to lay eggs:

• Keep up with routine parasite prevention

• Prevent tick bites and skin irritation

• Check your dog regularly for wounds or unusual changes

• Treat even minor skin injuries promptly

It’s also a good idea to stay ahead on medications, since demand can increase during outbreaks.

What this means going forward

The reappearance of New World screwworm is a reminder that animal health requires ongoing vigilance, even after past successes. The encouraging news is that we’re not starting from scratch—there’s strong awareness, established response systems, and experienced veterinarians who know how to identify and treat this condition.

For dog owners, the takeaway is straightforward: stay observant, act quickly if something seems off, and keep up with preventive care.

These simple steps don’t just protect your own dog—they also help limit the spread and support broader public and animal health efforts.

For the latest official updates, visit screwworm.gov and follow guidance from your veterinarian and local animal health authorities.