Livestock health officials say it could cost upwards of $13 million and take as long as two years to stop an incursion of fever ticks into the formerly fever tick free areas of five counties along the Texas-Mexico border. The fever tick, less than a 1/8-inch long, is capable of carrying and transmitting 'babesia,' a blood parasite deadly to cattle.
"For most of the country, the fever tick has been pushed out of sight, out of mind, since the 1940s. This tick, however, is capable of transmitting a foreign animal disease and it's sitting in our backyard," said Dr. Bob Hillman, Texas' state veterinarian and executive director of the Texas Animal Health Commission (TAHC), the state's livestock and poultry health regulatory agency.
"If we do not stop it, the fever tick could spread from coast to coast, except the arid lands of New Mexico and Arizona, and as far north as Washington D.C.," stressed Dr. Hillman. "As the tick spreads, so will the need for personnel and resources. Win the battle along the Rio Grande in Texas, and other states won't have to fight the war."
The TAHC has placed temporary fever tick quarantines on 1116.3 square miles in five Texas border counties, including parts of Starr and Zapata counties, and a contiguous area encompassing parts of Maverick, Dimmit and
Webb Counties. In addition, an 852-square mile permanent quarantine zone
butts up against the Rio Grande from Del Rio to Brownsville and is under the management of the U.S. Department of Agriculture's 60-person Fever Tick Force.
The USDA, which is adding up to 30 temporary tick inspectors, and the TAHC, which has detailed inspectors to south Texas on a rotating basis, are working with ranchers to locate, 'corral' and eradicate the tick. In this area about the size of Delaware, all cattle, horses, penned deer, llamas, camels and any other species that can host the tick are being manually inspected -or "scratched"--by TAHC or USDA inspectors.
If animals in these quarantined areas are moved from their premises, they'll undergo another "scratch" inspection, then be dipped or sprayed, and permitted for movement. Because horses can give ticks a lift, these animals are put under 14-day inspections and treatment, if they're moved routinely from their home base.
When fever tick-infested livestock are detected, the premises are quarantined for six to nine months. As of early October, this included at least 25 premises in the temporary quarantine areas and about 56 premises in the permanent quarantine zone.
Cattle remaining on tick-infested premises must be inspected and dipped every 14 days or treated with doramectin every 28 days. Alternatively, the animals may be moved to a new site, but only after undergoing two consecutive tick-free inspections and dippings. A movement permit then is issued, and the cattle must be transported immediately.
"The USDA has made $340,000 available for immediate fever tick needs in south Texas, and the state legislature granted the TAHC an extra $150,000 to purchase additional Co-Ral, the acaracide used for dipping vats and in spray rigs," Dr. Hillman said. He reported that a USDA assessment concluded that to eliminate fever ticks from the temporary preventive quarantine areas, at least $13 million was needed to hire additional personnel, repair or replace worn out portable tick dipping equipment, purchase new spray rigs and supplies, and procure other essential equipment.
"To get a handle on potential fever tick spread, the TAHC field staff also is tracing the movement of cattle from infested premises in the temporary quarantine area within the past year," Dr. Hillman noted. So far, this has involved nearly 800 animals, of which about 459 have been located, inspected and found to be fever tick-free. Some were found in Kansas or Texas Panhandle feed yards, and others were scattered across the state and to two other states.
"Many of these animals had been moved as calves without any identification, except the livestock market back tag, or clearly defined destination," he said. "This slows down our work, but we don't give up until all avenues are exhausted."
"The fever tick, by itself, will not cause disease. However, cattle tick fever is imminent if the fever tick is carrying babesia, and transmits it to cattle that are 'naïve,' meaning they have no resistance to the organism that quickly breaks down red blood cells," said Dr. Hillman. "There are two potential scenarios with fever ticks that keep the TAHC, the Tick Force and border ranchers awake at night."
The first scenario, explained Dr. Hillman, involves Mexico, where fever ticks and babesia have not been eradicated. Young calves there may be exposed to the babesia, survive the disease and develop immunity, but continue to carry the organism.
"Even if Mexican feeder cattle carry babesia, they will not cause a disease problem unless there is fever tick involvement," said Dr. Hillman, setting the scene for the scenario. "Mexican-origin feeder cattle enter the U.S. under strict USDA fever tick inspection and dipping requirements. To keep them away from fever ticks, the TAHC requires Mexican-imported cattle to have an "M" branded on their hip and prohibits these animals from being maintained in the permanent quarantine zone."
"If fever ticks are moved to sites where Mexican feeder cattle are pastured, the pests may pick up babesia. The babesia infected female tick transmits the disease to the next generation of fever ticks. Only one element then would be missing from the dangerous disease equation U.S. cattle with no immunity to the babesia," noted Dr. Hillman. "If native US cattle, which are susceptible to babesiosis or 'cattle tick fever,' are infested with babesia-infected fever ticks, then disease transmission to the native cattle will occur. Most likely, this will cause significant death loss of native cattle. It's crucial to keep the fever tick pushed beyond the border, and support and fund surveillance activities in the permanent fever tick quarantine zone."
Dr. Hillman said the second scenario involves wildlife as effective alternative hosts and sources for movement of ticks into Texas from Mexico and from the permanent quarantine zone to the free area of Texas. For once, noted Dr. Hillman, the beleaguered feral (wild) hog is not implicated. Fever ticks have not acclimated to swine, goats, sheep or dogs. On the other hand, elk, white-tailed deer, nilgai and red deer, serve as effective hosts for fever ticks, but are not affected by babesia.
"Free-ranging cervids do not respect national borders, shallow rivers, low fences, quarantines, or permits for movement," he said. "Wildlife hosts may crisscross the Rio Grande, hauling in fever ticks. Right now, wildlife presents the greatest risk for fever tick movement."
In spring 2007, more than 30 nilgai were depopulated in the Lower Rio Grande Valley National Wildlife Refuge, due to fever tick infestation. Twenty-eight of the 42 free-ranging white-tailed deer that were trapped and examined this year also were "ticky."
"Treating wildlife is a tricky proposition, because current methods are limited to feeding cervids ivormectin-treated corn or drawing them to 'four-poster' stations where they rub against pyrethrin-treated posts, which transfers the chemical," he said. "Ivormectin use requires a 60-day withholding period prior to slaughter or harvest, so wildlife feeding treatments will be delayed until hunting season ends."
In the meantime, the USDA or TAHC must inspect, treat and permit the movement of hides from deer or exotic hoof stock harvested on tick-infested or exposed premises. (Meat may be moved without inspection.) To avoid the possibility of transporting fever ticks, ranchers and hunters are urged to practice good sanitary measures when leaving a ranch. Brush off clothing to dislodge any ticks that may be on the fabric. Clean off boots and shake out jackets or items that have been on the ground.
"The fever tick is not a human health threat," said Dr. Hillman. "But be careful. Don't transport ticks to new sites. Getting and keeping the fever tick out of Texas and the U.S. is critical for disease control and our continued ability to move livestock without restrictions."
"If we are ultimately to be successful in our battle against the fever tick and 'cattle tick fever,' we must eliminate the current fever tick incursions in the free areas of Texas, then push the pest back into Mexico. To accomplish this, we must acquire resources necessary to fulfill the long-range fever tick eradication plan, fund research and develop additional treatment products and methods. We also must aid our Mexican neighbors in their fight against the fever tick and 'cattle tick fever,'" concluded Dr. Hillman.