As USDA halts animal imports, UF experts explain New World screwworm risk

The Florida Department of Agriculture and Consumer Services (FDACS) is urging veterinarians, livestock producers and animal health professionals to remain vigilant about recognizing signs and symptoms of the New World screwworm as the threat of its spread to the U.S. increases.

The screwworm could pose a threat to U.S. livestock, wildlife and domestic animals, especially those involved in U.S. food systems like beef and dairy cattle, according to FDACS. The threat is most serious to states with warm climates and abundant animal populations, such as Florida.

In light of the spread of the New World screwworm from Panama up through to Southern Mexico, the USDA has suspended live cattle, horse and bison imports into the U.S. from Mexico as of Sunday.

To help understand this insect, University of Florida experts explain what New World screwworms are, why they're a problem the U.S. has faced successfully before and how to be aware of signs of screwworm infections in your animals.

What is the New World screwworm?

The New World screwworm is a type of fly, scientifically known as Cochliomyia hominivorax. Its maggots are the main concern because they feed on the living flesh of warm-blooded animals.

A maggot is the larval stage of a fly — the small, worm-like insects that hatch from fly eggs. Unlike most maggots, which eat dead tissue and are helpful for decomposition, the New World screwworm maggot eats live, healthy tissue. Using an existing wound as a point of entry, they can burrow into a living animal with an existing open wound and cause serious, sometimes deadly, damage to the animal, said Andrew Short, UF/IFAS chair of the department of entomology and nematology.

The screwworm can infest livestock, pets, wildlife, sometimes birds, and — in rare cases — people.

All warm-blooded animals are at risk for a screwworm infection, especially if they have a recent, exposed wound or have just undergone surgery.

When is the last time the U.S. had a screwworm outbreak?

New World screwworms were in the U.S. since before the Civil War until they were eradicated in 1966, Short said.

In 2016, an infection spread in a population of Key deer in the Florida Keys. The infection continued until early 2017, when sterile fly treatment was successful in eliminating the screwworms from the environment.

There are currently no reports of New World screwworms in the U.S.

Is a screwworm infection treatable?

Yes, New World screwworm infections are treatable. In humans and domesticated animals, treatment usually involves medical or veterinary procedures to physically remove the larvae. In wildlife, control efforts focus on eliminating screwworm flies from the environment.

How do you get rid of New World screwworms in an area?

The eradication of New World screwworms is done through releasing sterilized flies into the environment, which mate with the local New World screwworm populations, stopping further reproduction. The population of New World screwworms then dies out.

What are the symptoms of a New World screwworm infection in animals?

The symptoms in animals with a screwworm infection include irritated behavior, especially related to a wound, head shaking, biting at an open wound, the smell of tissue decay, maggots in the wound, a large red bump caused by fly strike, signs of depression such as not eating, decreased milk production and seclusion from the rest of the herd.

The early symptoms can be difficult to see, but the most obvious sign is a change in the wound's appearance, where the wound gets larger and deeper. It may also smell and have some bloody discharge, according to FDACS.

Animal and livestock owners who suspect a screwworm infection should isolate the animal and contact their veterinarian immediately, said Dr. Fiona Maunsell, clinical associate professor in the UF College of Veterinary Medicine. Concerns should also be reported to the State Veterinarian's office. Owners should never treat a maggot-infested wound without contacting their veterinarian or the State Veterinarians' office first, as this could delay rapid detection and control of an outbreak, Maunsell said.

While any animal can be infected, animals that spend the majority of their time outside — and especially those that give birth outside — are at a greater risk due to open wounds. To prevent this, keep wounds dry and covered and report any signs of disease to your veterinarian.

How can I report a New World screwworm infection?

Early detection and reporting are essential, said Florida State Veterinarian Dr. Michael Short in an FDACS press release.

"The earlier we catch a potential case, the better chance we have of containing it. We're asking everyone who works with animals, whether in private practice or in the field, to take a second look at any wound that is unusual or doesn't heal as expected," he said.

To report cases of New World screwworm infection in livestock or pets, contact:

· Phone: 850-410-0900 (during office hours) or 800-342-5869 (after hours)

· Email: RAD@FDACS.gov

· Online: www.FDACS.gov/RAD

To report a suspected screwworm infection in wildlife, call the Florida Fish and Wildlife Conservation Commission (FWC) at 888-404-FWCC (3922) or email the Wildlife Health Team at WildlifeHealthTeam@MyFWC.com.

For more information, resources and updates, visit FDACS.gov/NWS.

Provided by University of Florida