Invasive Flesh Eating Pest in U.S. Puts South Dakota on Alert

A major agricultural threat has officially re-entered the United States, prompting regional livestock officials to urge local producers to ramp up herd inspections.

The U.S. Department of Agriculture (USDA) recently confirmed a case of the New World screwworm in Texas, marking the first locally acquired case of the invasive, flesh-eating pest in the continental U.S. in decades. With summer grazing and interstate livestock shipping entering peak season, South Dakota officials are warning ranchers that vigilance is critical to keeping the destructive parasite out of the state.

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What is the New World Screwworm?

Credit: Canva

Unlike typical fly maggots that only feed on dead or decaying tissue, the New World screwworm is an aggressive parasite that feeds (almost entirely) on the live flesh of warm-blooded animals.

A female screwworm fly will target any open wound on an animal, ranging from a fresh branding mark on cattle or a minor tick bite to the unhealed navel of a newborn calf. She lays her eggs at the wound's edge, and within 12 to 24 hours, the larvae hatch and use sharp mouth-hooks to burrow deep into the living muscle tissue. If an infestation goes unnoticed and untreated, it can easily turn fatal for an adult animal in less than two weeks.

Why South Dakota is on Alert

Credit: Canva

The U.S. successfully eradicated the pest way back in 1966 by using an immense sterile insect breeding program. However, in the past year, a series of outbreaks pushing north through Central America and Mexico ultimately led to this week's confirmed case in Zavala County, Texas.

Because the adult flies have a limited natural flight range, the primary threat to South Dakota isn't the insect flying north on its own. Instead, state veterinary officials are concerned about interstate livestock transportation. An animal could easily be loaded onto a trailer in a southern state with an unnoticeable, early-stage infestation of the screwworm fly, then be transported across state lines into the Upper Midwest before the larvae are even visible. This is the concern that has health officials across the entire country on high alert.

While the screwworm cannot survive a harsh South Dakota winter, a localized outbreak during the peak summer grazing season could cause severe economic damage to regional producers before the first hard freeze.

To learn more about potential risks and to hear an interview with South Dakota State Veterinarian Dr. Mendel Miller, visit the South Dakota Cattlemen's Association website.

Story Sources: South Dakota Cattlemen's Association Website, CDC Website