Mexican cattle banned from Texas due to screwworm threat

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A single cow in Mexico and a pest the size of a housefly have held up pens full of Texas-bound cattle worth millions of dollars for the past six weeks.

The U.S. Department of Agriculture has banned Mexican cattle imports since November after a parasite known as screwworm, which wriggles into the flesh of livestock and kills them if left untreated, was discovered on a cow near Mexico’s border with Guatemala. The ban on imports is a bigger problem than the screwworm itself, according to Texas Agriculture Commissioner Sid Miller and some Texas cattle ranchers, who say closing cattle imports damages their livelihoods, bottlenecks beef production and could increase beef prices for consumers.

“I get calls every single day from people asking for cattle,” said Alvaro Bustillos, president of Vaquero Trading, a livestock procurement company in El Paso. “Key steps in the production value chain are being stopped because people cannot source cattle.”

Miller remembers a time when screwworm wreaked havoc in Texas — $132 million in damages in 1976 — but said the USDA prematurely closed imports and is hampering an industry still trying to recover from two years of widespread drought.

“There’s no way we are going to get screwworm,” Miller told The Texas Tribune. “We have a very strict import process for these cattle.”

About 3% of U.S. cattle come from Mexico. But Mexican cattle play a disproportionate role in southern states’ beef production. Approximately two-thirds of Mexican cattle imports remain in Texas, New Mexico or Oklahoma, according to an estimate from Ben Weinheimer, the president and CEO of the Texas Cattle Feeders Association, which represents the industry across those three states.

Cattle crossing between Mexico and the U.S. remains on hold while the USDA installs new inspection pens and enhanced safety protocols to ensure cattle are healthy. Keeping the U.S. free of screwworm saves livestock producers close to $1 billion a year, said Texas Animal Health Commission spokesperson Erin Robinson, pointing to a USDA estimate that accounts for costs of labor, treatment, veterinary care, eradication efforts and loss of production.

Shutting off Mexican cattle imports has contributed to a recent increase in cow prices, said David P. Anderson, a professor of agricultural economics at Texas A&M University AgriLife Extension. Prices of feeder steers, which make up a large portion of Mexican cattle imports, are forecast to rise by 8% in 2025, a USDA report states. If import restrictions continue for much longer, beef production could drop, pushing up prices for consumers.

“Fewer cattle mean higher beef prices, increasing inflation at the checkout line,” Miller wrote in a Dec. 23 editorial, adding that the ban “could send shockwaves through the beef market.”

Screwworm infestations occur when a female fly lays her eggs on an animal’s open wound or another area such as their eyes or mouth. The female can lay up to 300 eggs at a time, and any warm-blooded animal, including humans, although rare, can be affected. The eggs hatch into larvae that dig into the animal and feed on living flesh.

Screwworm was declared eradicated from the U.S. in 1966, but Texas experienced a more recent outbreak in 1976 that affected 20% of cattle.

Farmers disrupted

When Bustillos found out the weekend before Thanksgiving that imports of Mexican cattle were to be halted because a single cow had screwworm, he was upset.

“Based on what is happening 3,000 kilometers down south, they are shutting us down,” Bustillos said. “I don’t think it’s fair.”

Bustillos has a stake in both exporting and importing cattle. He’s board chairman and president of the Chihuahua Cattlemen’s Association, which represents Mexican cattle producers. He also leads Vaquero Trading, which imports more than 200,000 Mexican cattle a year and supplies cows to feedlots in several states.

Bustillos says he has worked hard to build trust between the U.S. and Mexico, putting in place millions of dollars worth of sanitation practices that keep livestock safe and pest free on both sides of the border. Cattle entering the U.S. must have health certificates, vaccinations and testing to prevent diseases from entering the U.S, per requirements from the USDA’s Animal and Plant Health Inspection Service.

November and December are typically when the U.S. imports the largest number of cattle from Mexico. Most of those imports are small cows headed to ranches or feedlots, where they are fattened up before getting sent to packing plants for beef production.

The U.S. has steadily increased Mexican cattle imports over the years. In 2023, about 1.1 million cattle entered from Mexico, up from about 870,000 the year prior. An extended drought coupled with higher U.S. cattle prices contributed to that increase, said Anderson, the economist.

“We have the smallest cow herd in the U.S. since 1961, so we have higher prices here,” Anderson said about Texas’ cattle industry. “That makes us an attractive market for Mexico to sell to.”

Federal officials have not specified when cattle shipments will resume, but a USDA spokesperson said in late December that shipments would resume “incrementally after the New Year, with full resumption sometime after that.”

“Protecting American livestock from foreign pests is our top priority,” the spokesperson said in an email.

Anderson said he does not expect consumers to see significant increase in beef prices if trade resumes this month.

For Bustillos, the longer the shutdown continues, the more concerned he grows about the market. Cows are imported at certain times of year based on their weight and the availability of grass for them to graze. If the border does not reopen soon, he says, cattle could start to lose value.

For now industry leaders are hopeful trade opens up soon.

“The hope is that in January we’ll start to see some semblance of normal trade,” Weinheimer said.

‘We don’t want them back’

Anderson has heard enough stories about screwworm from his father to know the damage they can bring.

“Every day they had to grab each pig and look for wounds and sores,” he said. “They’d clean them out and put medicine on…It was horrible.”

So Anderson says it makes sense for the USDA to address screwworm before it’s anywhere near the U.S.

“It would cost more to eradicate them if you let the problem grow bigger,” he said.

The screwworm is eliminated by dropping sterile male flies from airplanes over large areas. Female screwworm flies mate only once in their lifetime, so the loads of sterile male flies caused the population to eventually die out. That method is the only way to eradicate the screwworm today, according to the USDA.

Jim Schwertner, who operates a ranch in Williamson County, was a young boy helping run his family business when the sterile fly technique was introduced in Texas. He said it was a game changer and eliminated the screwworm within a year.

“When they finally eradicated it, life was a whole lot easier for my dad and his cowboys,” Schwertner said.

Schwertner recalled treating cattle hit by screwworm. “You’d put insecticide on with a paintbrush to keep the screwworm off the cattle,” he said. “It was a lot of work and really expensive.”

The technique has been used to create a biological barrier against the screwworm in Panama. But the pest has exploded there and crept northward in recent years, spreading through Costa Rica, Nicaragua, Honduras and Guatemala. Texas and U.S. animal health officials attribute the spread to new areas of farming and increased cattle movement. Federal officials approved a $165 million emergency investment last month to stop screwworm from entering the U.S. and to help partners in Mexico and Central America eradicate it.

The eradication of screwworm has likely preserved Texas’ wildlife population. As recently as 2016, a resurgence of screwworm in the Florida Keys killed more than 130 deer before the pest was eliminated from the region the following year using the sterile fly technique.

The Texas Parks and Wildlife Department has asked hunters and outdoor enthusiasts in South Texas to monitor for animals affected by screwworm. Any wildlife with signs of screwworm are to be reported to a local biologist. No cases have been confirmed in Texas, a spokesperson for the Texas Animal Health said.

Disclosure: Texas A&M University, Texas Cattle Feeders Association and Texas Parks And Wildlife Department have been financial supporters of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune's journalism. Find a complete list of them here.