Cattle fever tick threatens herds in South Texas
Imported antelope, deer are spreading the parasite
SAN ANTONIO — The nilgai, a once-exotic antelope imported from Asia for zoos and let loose for trophy hunts on Texas ranches, are now being blamed for spreading the potentially devastating cattle fever tick the farthest into the U.S. interior in decades, possibly since it was declared eradicated in 1943.
The Laguna Atascosa National Wildlife Refuge in lower Cameron County, about 2 miles north of the Mexican border at the southernmost tip of Texas, is being called ground zero for infested nilgai and white-tailed deer, which also are hosts. The park came under quarantine after the tick was found on the carcasses of hunted game in 2014.
While the U.S. has strict rules requiring infected animals to be quarantined and treated to keep the ticks from spreading, Mexico does not. And the nilgai, cattle and other hosts for the nefarious fever tick roam unchecked across the border. The situation is especially grave because the animals are free-ranging
and compromise ongoing eradication efforts such as systematic treatment or moving cattle out of infested pastures. According to the U.S. Department of Agriculture, an extended tick outbreak could cost U.S. ranchers and the broader economy more than $1.2 billion in extermination expenses and lost revenue from diseased animals.
It’s estimated that 70 percent of white-tailed deer and nearly 70 percent of nilgai on the refuge are infested, prompting officials to require that animals killed by hunters be tested and skinned on site, freezing the heads that are kept for mounting for 24 hours to kill the ticks. In the last year, the U.S. Department of Agriculture has contracted with helicopters and sharp shooters for aerial attacks that have so far killed about 200 of the nilgai.
More aerial harvests are planned for the nilgai, refuge manager Boyd Blihovde said.
“We’ve already done in my opinion quite a lot and we’re going to continue do our part whenever we can,” he said.
But the damage may already have been done. Without natural wildlife predators, the nilgai population has exploded in South Texas, and female nilgai have been known to migrate as much as 30 miles.
Neal Wilkins, CEO of the East Foundation, said 27,000 acres of the Foundation’s 200,000-acre ranch in South Texas are under quarantine because the parcel is adjacent to an infested property.
“It’s kind of the front lines there in keeping the fever ticks from traveling north,” he said.
He counts the portion of State Highway 186 that runs east from Raymondville to the Gulf Coast town of Port Mansfield, his ranch’s southern boundary, as the last natural barrier to infected nilgai migration. After that, he said, there are no natural barriers until Baffin Bay.
In between are about 2 million acres of large ranchland that’s at risk should the tick spread beyond Highway 186, including parts of the storied King Ranch, which is at 825,000 acres one of the world’s largest ranches and in a twist of irony was one of the first to sport the nilgai.
Cattle fever ticks (Rhipicephalus microplus and Rhipicephalus annulatus) are carriers of bovine babesiosis, or “cattle tick fever,” which in the early 1900s wiped out 90 percent of U.S. cattle from Pennsylvania to California, causing about $130 million in losses.
Infected cattle experience bloody urine, diarrhea, fever and extreme anemia before dying. The antelope were imported from India as zoo animals and released in South Texas as prized game for hunters in the early 1900s, according to the Texas State Historical Commission.
Tick fever was already a problem; The Texas Animal Health Commission was established in 1893 as the Live- stock Sanitary Commission to try to get control of the disease.
Through quarantines and dips — the first was a petroleum solution from the Beaumont oil fields — the fever tick was in 1943 declared eradicated save for a narrow permanent quarantine zone along the Rio Grande.
To aid the effort, a force of federally employed “tick riders” set out each day on horseback, patrolling 8to 10-mile sectors to lasso cattle that swam the Rio Grande from Mexico into the U.S. and were possibly transporting the tick. Those measures helped keep it contained for 56 years.
But in 1999, the ticks started to spread onto ranchland beyond the permanent quarantine lines.
Several factors were blamed. For one, tick riders were redeployed to help fight wildfires and other livestock disease outbreaks in other states, leaving areas unprotected from stray Mexican cattle. For another, the growing trend of stocking ranches with exotic game introduced a new class of hosts for the ticks.
In 2007, the U.S. Department of Agriculture had to expand quarantine zones in three places. The largest, the “Carrizo Zone,” extended deep into Dimmit County, the others were in Starr and Zapata counties. Those outbreaks have since mostly been contained, but the latest outbreak has livestock experts calling for a new approach.
The Texas Animal Health Commission said there were 15 infested properties in Cameron County and eight in Willacy County as of Feb. 16.
The commission issued a proposed rule introducing a fever tick vaccine into the arsenal of dips, patrols and widespread inspections that ranchers say will be onerously expensive and impossible to administer.
Ty Keeling, a Pleasanton rancher, said a single roundup costs about $1,750 per thousand acres. That covers two hours of helicopter time and two days of ranch hands on horseback trying to get what the helicopters miss. The TAHC didn’t respond to requests for comment on the rule language.
The vaccine is derived from the gut of the tick, and produces an antibody response in the cattle that prevents the ticks from absorbing the proteins in the cows’ blood. They essentially starve.
“The reason for the proposed change is to authorize the TAHC to utilize the vaccine,” agency spokeswoman Callie Ward said in an email. “The vaccine is not a silver bullet. The value of the vaccine is in its prolonged ability to kill or impair ticks to the point of not completing their life cycle, thereby greatly reducing the number of ticks in the environment.”
Felix Guerrero, an insect physiologist at the USDA’s Tick and Biting Fly Research Unit in Kerrville, said the ticks are damaging even if the cows don’t manifest the disease.
“The ticks feeding on wild animals or a cow do cause damage and do affect the animal’s productivity and comfort, just from blood loss and irritation,” he said. “They don’t feed. They’re uncomfortable.”
Wilkins, of the East Foundation, said infected cows can do a rancher in.
“The bottom line is if our cattle are positive for fever ticks then it threatens international trade and threatens our ability to trade with other states,” he said.
But while cattle raisers support the vaccination program, they are incensed by language in the TAHC’s rule that requires 100 percent of a rancher’s herd be rounded up and treated with a vaccine that requires two primary doses 28 days apart, with boosters every six months. Ranchers say the requirements aren’t realistic and that it’s time to rethink the rule, especially as the ticks encroach on areas with larger herds.
“It’s not economically possible to gather 100 percent of your cattle in those remote and rough conditions that you find in that big country in that part of South Texas,” he said.
Keeling agreed, saying that even with helicopter and cowboy roundups, some cattle are going to be missed. Periodic roundups are considered a standard cost, but not if they have to be conducted for days on end, he said.
“These are really large pastures,” he said. “You can imagine you have a wet year like this year, you have a lot of vegetation and lots of places they can hide.”