These cowboys aren't after the wave of drug smugglers or illegal immigrants who cross the border daily: They're inspectors on the lookout for border-crossing, blood-sucking parasites that feed on the region's cattle and deer – small black ticks, or garrapatas.

The fever tick was all but stricken from the U.S. more than 50 years ago, after wreaking havoc on the state's beef industry.

But experts warn that they are back and stronger than ever after developing a resistance to pesticides that had been used effectively for decades. And left uncontrolled, the parasites could result in losses to the beef industry of up to $1 billion a year, the experts warn. They spread a debilitating disease that destroys red blood cells.

Enter the 61-person Fever Tick Force, a group of modern-day cowboys funded by the U.S. Department of Agriculture who patrol a thin quarantine line along the Rio Grande.

Earlier this month, the Tick Force temporarily expanded the quarantine zone – which stretches from Brownsville to Del Rio – to include portions of Eagle Pass stretching to Carrizo Springs after seeing more and more ticks outside the zone.

It was the second such expansion this summer.

The tiny black ticks from northern Mexico, along with the dreaded "Texas fever," are spreading to new hosts – the European red and Mexican white-tailed deer and nilgai, which are abundant in South Texas – said Ed Bowers, the head of the Agriculture Department's fever tick eradication program.

"Deer don't have pastures. They don't respect fences," Mr. Bowers said. "They just have territories which might cross the borderline."

At the turn of the century, cattle drives through Texas were nearly wiped out by piroplasmosis, or "Texas fever."

Some Texas cattle, particularly along the border with Mexico, were mostly immune. But cattle bred in North Texas and beyond were not. At its height, the Texas fever killed 90 percent of yearling and adult cattle herds in a matter of days.

Source: Dallas Morning News