New World Screwworm (NWS) in Dogs: September 2025

What is New World Screwworm?

New World Screwworm (NWS) is a type of fly whose larval stage (maggots) burrow into the living flesh of an animal as they feed. This is different from most types of maggots that only feed on dead tissue. NWS can infect livestock, pets, wildlife, birds (occasionally), and humans (rarely).

Why is NWS in the news?

NWS is not usually found in the United States. Preventing the spread of NWS into the United States is critical for protecting the livestock industry, economy, and food supply. Recent outbreaks of NWS in Central America and Mexico have caused the United States Department of Agriculture (USDA) to implement an aggressive NWS outbreak prevention program, including limiting the movement of livestock across the US southern border.

Has there been NWS in the United States before?

NWS was eradicated from the United States in 1966 using sterile flies that cannot reproduce. This technique remains one of the most successful and important tools to preventing NWS from spreading back into the United States. NWS is still common in parts of South America, Cuba, and the Dominican Republic and is spreading northward into Central America and southern Mexico. It is important to keep NWS from reentering the United States. In 2017, there was a small outbreak of NWS in the Florida Keys that was eliminated using sterile flies that cannot reproduce.

What species can get NWS?

NWS can infest livestock, pets, wildlife, birds (occasionally), and humans (rarely). NWS is most often detected in cattle, swine, horses, sheep, goats, and dogs.

How do animals get NWS?

Animals get NWS when a New World Screwworm fly lays eggs on the animal, which then hatch into larvae. The larvae eat into the flesh of the animal, causing wounds which may attract more flies and may become infected. NWS flies are attracted to wounds. Animals that have recently suffered an injury, had a surgical procedure, been bitten by a tick, or given birth are most vulnerable.

What are the symptoms of NWS?

NWS infection is most often associated with the presence of a pre-existing wound, but may also be found in mucous membranes, such as around the eyes, nose, gums, and genitalia. NWS maggots may be visible in the affected area. Affected areas may have a bad smell, bloody discharge, or pus.

How can I keep my pet from getting NWS?

The risk of NWS to pets is minimal in the United States. The best way to prevent NWS is to pay attention to your pet and seek care with a veterinarian any time you notice a wound, or your pet is showing signs of pain including depression, irritability, not eating, or isolating away from other animals or people.

Can NWS be treated?

Yes. NWS is treatable but may require extensive and painful wound care. Wounds left untreated may develop serious infections. The sooner a case of NWS is identified, the easier it is to treat.

Can animals die from NWS?

If left untreated, NWS infections can become bad enough to cause death. You should seek veterinary care right away if your pet has an open wound, maggots, or is showing signs of pain including depression, irritability, not eating, or isolating away from other animals or people.

Can people get NWS?

In rare cases, there have been cases of NWS in people. Seek care with a healthcare provider if you have a wound or injury or are concerned that you may be infected with NWS.

What do I do if I think my pet has NWS?

You should seek veterinary care right away if your pet has an open wound, maggots, or is showing signs of pain including depression, irritability, not eating, or isolating away from other animals or people. Tell your veterinarian if you have seen maggots on your pet so that they can provide proper treatment. To find your nearest VCA, visit our hospital locator.

Isn't NWS just a livestock disease?

No. While NWS poses the biggest threat to livestock and our agriculture industry, NWS can affect all mammals, including pets and, rarely, humans.

Additional questions about New World Screwworm?

For additional details and the most up-to-date information about NWS, visit the USDA and CDC websites.