In cattle fever tick fight, scientists enlist Vietnam’s help

RIO HONDO — Killing the cattle fever tick in South Texas is going international.

Six ranches east of this city, comprising 40,000 acres of pasture and brush lands, have embarked on a project to use 150 motion-activated sprayers to spritz nilgai with a slurry of nematodes which invade and kill cattle fever ticks.

Yet when it comes to killing cattle fever ticks, researchers are hedging their bets and seeking more firepower from Asia.

John Goolsby is a tick expert with the U.S. Department of Agriculture who has been working on the cattle fever tick problem in South Texas for the past three years, a time frame he calls “not long” by scientific standards.

Now, he says, an international project based in Vietnam at the National Institute of Veterinary Research is moving forward on another frontier when it comes to killing the tick — parasitic wasps.

Cattle fever ticks are smaller than the usual brown dog ticks we commonly see. The tick spends its three life stages — larva, nymph and adult — on cattle and also ungulates like nilgai and white-tailed deer, according to the Department of Animal Science at TAMU.

Females partake of a blood meal, drop to the ground, and lay as many as 4,000 eggs. These hatch into larvae which then attach themselves to cattle, nilgai or deer.

It is in their nymphal stage where the wasp’s larvae strike, invading the tick and killing it.

“We’ve hired a consulting entomologist in Hanoi who’s a Belgian entomologist, a bio-control specialist who was trained at Purdue,” Goolsby said in a recent interview.

Goolsby traveled to Hanoi last fall to see the operation.

“We’re going to do host exposures and collect the ticks and have got the local farmers signed up,” he said. “In February, they’ll start in earnest with repeat exposures to cattle fever ticks.”

Cattle fever ticks, like the nilgai antelope which were brought to Texas on the King Ranch in the 1930s, are both Asian natives and it makes sense to search for tick antagonists in their home range.

They’re back

South Texas is in the middle of one of the periodic irruptions of the cattle fever tick which spread north out of Mexico, where it is endemic.

The fever ticks can carry a disease fatal to cattle called babesiosis, which has been a potentially catastrophic threat to ranchers and to Texas’ $12 billion-a-year beef industry.

In the latest tick foray northward, no “hot ticks” which carry the microscopic parasite which causes cattle fever have been found.

But with the stakes so high, all of Cameron and Willacy counties are at present in a temporary cattle fever tick quarantine zone.

Researchers learn

Goolsby said research in Vietnam already has brought forth some surprises.

“We also found out that the parasitoid actually emerges from the engorged nymph,” he said. “What you’ve seen are the big and engorged females, they’re all females. I met the scientist from Germany who’s been doing the same thing over there on black-leg tick in Germany so she’s been rearing them.

“They almost all emerge from this engorged nymph stage,” despite what one sees in the scientific literature, Goolsby said.

The Vietnamese project will infest cattle there with the cattle fever tick and the wasps will be released to do their damage.

If successful, the plan is to bring these wasps to the United States, and gain approval to release them in areas now under quarantine to create a second front against the cattle fever tick.

In addition to the ranchers in eastern Cameron County, partners in the spraying project are the conservation group Las Huellas, the Caesar Kleberg Wildlife Research Institute at TAMU-Kingsville and the U.S. Department of Agriculture.

Cattle fever tick facts

In the late 1800s, Texas cattle fever caused extensive livestock losses. To combat this deadly disease caused by ticks, the Bureau of Animal Industries, predecessor of the USDA, developed the first tick eradication program in 1906. When ticks were controlled across the southeastern U.S., the USDA and Texas Animal Health Commission established a permanent quarantine zone along the Texas-Mexico border in 1943. Tick eradication was the preferred control method.

Two ticks, Rhipicephalus annulatus and R. microplus, can carry microscopic protozoan parasites, Babesia Bovis or B. bigemina, which cause Texas cattle fever. The parasites attack red blood cells, causing the animal to develop anemia, high fever and enlargement of the liver and spleen. It is fatal to some 90 percent of susceptible cattle. Although the protozoan is not in the United States, they are active in Mexico and other countries. Mexican cattle are more resistant to the parasite.

Source: Department of Animal Science, TAMU