Photo courtesy of Terry Neal

Fever Tick Outbreak Prompts Harvest of Exotic Nilgai

An outbreak of fever ticks is prompting the United States Department of Agriculture (USDA) to harvest an infested population of exotic nilgai antelope on wildlife refuge property near the mouth of the Rio Grande. The disease these ticks sometimes carry does not affect humans but can be fatal to cattle. The helicopter hunt is set for the last week in March, weather permitting, and targets all nilgai on United States Fish and Wildlife Service land encompassing some 20,000 acres between the Brownsville ship channel and the river.

"On February 15 a nilgai was shot on private property near Fish and Wildlife land, and it ended up on the refuge," said Ed Bowers, USDA Director of Field Operations for the Cattle Fever Tick Eradication Program. "They called an inspector, and he found fever ticks."

The southern cattle tick (Boophilus microplus) is the pest responsible for disease in the Rio Grande Valley. The adult ticks are small and vary in color from olive green to mottled yellow or olive brown. They cluster on grass and other plants where they wait for a host to pass by.

"It could spread like wildfire if we do not take action," said Jim McAllen, cattle rancher and local Director of the Texas and Southwestern Cattle Raisers Association and Chairman of the Fever Tick Committee. "It could be devastating to cattle and horses."

Livestock affected with the chronic form of cattle fever develop a mild fever and stop eating. They lose weight rapidly, become anemic and some die. Infected cattle frequently relapse and often become susceptible to other diseases.

Cattle fever ticks are thought to have been introduced to the New World on livestock owned by Spanish colonists. The ticks are capable of carrying and transmitting bovine babesiosis, once called "Texas fever." In 1868 a disastrous outbreak of cattle fever killed some 15,000 head of cattle in Illinois and Indiana. The importation of cattle to these states from Texas is thought to have caused the outbreak. At the time, Texas cattle had apparently developed some immunity to the disease due to frequent exposure to fever ticks. However, cattle being driven to northern markets brought infected ticks. Resident cattle had no immunity and thousands became infected and died.

Bovine babesiosis led to the creation of a National Fever Tick Eradication Program in 1906. Texas and 13 other southern states participated in quarantines and chemical dipping of cattle. By 1943 the eradication campaign had been completed north of the border. However, according to the USDA, fever ticks remain widespread in Mexico and continue to pose a threat to United States livestock. Therefore, a permanent quarantine zone remains along the Rio Grande in South Texas, ranging in width from several hundred yards to approximately 10 miles.

While there have been numerous outbreaks of fever ticks on cattle in South Texas in recent years, a 1998 outbreak in Zapata County was the last instance where cattle were infected. "It was a small herd of a dozen or so cattle, and I recall two or three died, but we took care of it immediately," Bowers said.

A 500 mile swath of land stretching form the mouth of the Rio Grande to Del Rio is patrolled by 61 "tick riders". These men on horseback are employed by the USDA, and they are the nation's first line of defense against an outbreak of cattle fever.

The mounted inspectors conduct range inspections of premises within the quarantine zone, and roundup stray cattle that may have crossed the river from Mexico. Inspectors "scratch" suspect livestock for ticks, using their fingers to search the skin of an animal form head to tail. Tick inspections are also performed at seven South Texas livestock markets near the quarantine zone to help ensure that cattle from the border are free of ticks before being sold and transported to northern markets.

Before leaving the quarantine zone all cattle must be scratched and declared tick-free and dipped in coumaphos, an organophosphate acaricide. Horses leaving the zone are also inspected and treated prior to movement, but they are sprayed rather than dipped.

When fever ticks are found on livestock the property of origin is considered infested and placed under quarantine. According to the USDA, the owner is given two options: (1) Leave the cattle on infested pasture and scratch and dip them every 14 days for six to nine consecutive months to ensure that all ticks are removed from the pasture; or (2) Process the cattle with two successive 'clean' dippings, 10 to 14 days apart, where no ticks are fond prior to dipping. The pasture is then vacated of all livestock for a period of 6 to 9 months or longer to break the lifecycle of the ticks.

Due to the cost and trouble of successive dipping most ranchers decide to vacate their pasture. However, as a result of emptying pastures, there has been an apparent increase in the occurrence of ticks on wildlife, most notably white-tailed deer and nilgai. Although cattle are the preferred host of fever ticks, the parasites are capable of surviving on deer and some exotic ungulates such as nilgai.

Nilgai antelope are native to India and were introduced to South Texas by the King Ranch in the 1930's. Adult males can top 600 pounds, and in their adopted country they have no natural predators. The large animals are adept at going under or thru fences. They have gradually increased their range from north of Raymondville south to the Rio Grande. These exotic animals have adapted so well to the coastal prairie that on some ranches along the coast east of Highway 77 they outnumber native whitetail deer and in time of stress compete with whitetails for available browse.

They are hunted aggressively on South Texas ranches but are extremely wary and difficult to stalk. Sportsmen admire them for the challenge they pose. Mature bulls command a price of $2,000 plus and provide a valuable source of income to ranchers. Nilgai are highly regarded table fare, and their lean and tasty meat is becoming increasingly popular. Despite conventional hunting pressure, nilgai have continued to multiply. The cows, or females, in particular are annually harvested on a commercial basis by helicopter on several coastal spreads.

"They moved into the area near the river about six or seven years ago and probably crossed the ship channel," Bowers said. "We have had a tick rider or two see them go across the river. Nilgai are considered livestock under Texas law and the owner of the land where the animal's occurring are required to vacate the property of those animals that are capable of carrying the fever ticks or present them 100 percent for treatment every two weeks for six months."

The wild and elusive antelope are not candidates for dipping and consequently harvest by helicopter is the only viable means to eliminating them and the ticks they carry. Last year the USDA harvested 22 nilgai by helicopter form refuge land near Boca Chica and no fever ticks were found. Nearly 2,000 pounds of field dressed meat was delivered to the Valley Food Bank.

"We fully support the efforts of the USDA to eliminate nilgai from refuge property," said Ken Merritt, Project Leader for the South Texas Refuge Complex. "We do not want to be a conduit for disease, and we want to be good neighbors to the cattle industry."

The plan is to eliminate all the nilgai between the ship channel and the river where some 20 animals are thought to reside. The USDA has contracted the harvest to a private helicopter hunting service, and the animals will be quickly butchered by ground crews and refrigerated on location in specialized trailers for distribution once again to the Rio Grande Valley Food Bank. Bowers hopes to complete the harvest in a day and estimates the cost will run approximately $5,000 to $6,000.

No hunting is planned on private land. "Since the refuge owns the bulk of the property that should take care of the problem since these are herd animals," Bowers explained.

Nilgai will not come to feed, but white-tailed deer on refuge property will be fed treated corn from feeders placed near freshwater sources. The ivermectin-treated corn is very effective in preventing the ticks from infesting deer.

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Copyright 2007 Richard Moore