According to a revised and re-issued environmental assessment last week, failure to take action to reduce the population of free ranging and tick-infected Nilgai antelope near the mouth of the Lower Rio Grande River in deep South Texas would likely open the door to re-infestation of cattle fever ticks into other and adjacent parts of lower Texas. Consequences to the state's vibrant cattle industry could be dire.
The new environmental assessment followed a public comment period addressing the wildlife removal. With the new report in hand, the United States Department of Agriculture Animal and Plant Health Inspection Service's (USDA-APHIS) Veterinarian Services (VS) division is more convinced than ever that failure to decrease the number of nilgai population in a small area of Deep South Texas could result in the spread of Texas Cattle Fever on more U.S. soil.
The cattle fever tick (R. annulatus) and the southern cattle tick (R. microplus) (both referred to as “cattle fever ticks”) are agricultural pests of concern for U.S. livestock. Cattle fever ticks infest cattle, and—occasionally—horses, mules, sheep, goats, deer and certain exotic species, including Nilgai.
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The ticks must have blood from an animal host to complete their life cycles. As they feed, these ticks spread protozoan parasites of the genus Babesia (blood parasites), the causative agent of babesiosis, also called Texas fever, tick fever, redwater, or bovine piroplasmosis. Bovine babesiosis is caused by at least two of seven Babesia species that infect cattle—B. bigemina and B. bovis. The ticks acquire Babesia infection from feeding on infected cattle. The infection settles in the ovaries of the ticks so larvae from infected female ticks carry the infection as well.
The ticks and their associated diseases, especially bovine babesiosis, or cattle fever, pose serious problems to warm-blooded animals. Babesiosis is generally characterized by extensive loss of red blood cells due to breakdown of the cellular membrane. This leads to anemia, jaundice, and death. Infected cattle may exhibit neurological disturbances characterized by incoordination, seizures, muscle tremors, hyper excitability, aggressiveness, blindness, head pressing, and coma. In addition, the two cattle fever tick species are capable of causing blood loss, significant damage to hides, and an overall decrease in the health condition of livestock.
As early as last year, animal health officials had become concerned with the growing number of free-roaming Nilgai antelope that populate the Boca Chica area on the tip of Texas where the Rio Grande empties into the Gulf of Mexico. First brought to the King Ranch as a desirable exotic for hunters, the Nilgai are resourceful animals and have spread far and wide across South Texas.
History of cattle fever
The cattle fever tick was first introduced to the New World through livestock brought from other countries by colonists and explorers in the early 1500s. These and related tick species once occurred in large areas of the United States and still occur in a permanent quarantine or “buffer” zone, referred to as the Permanent Tick Quarantine Zone of South Texas. They can readily be found in Mexico and throughout tropical and subtropical regions of the Western Hemisphere.
In the late 1800s, the association between cattle fever ticks and “Texas fever” was identified by scientists. In the early 1900s, when large areas of the United States were affected with the cattle fever tick and the southern cattle tick, the U.S. Congress initiated a tick eradication program. Established in 1906, the Cattle Fever Tick Eradication Program (CFTEP) was the first cooperative State-Federal eradication effort and remains active today, especially in Texas.
Today, a federal "buffer" zone extends more than 500 miles from Del Rio, Texas, to the Gulf of Mexico, and ranges from 200 yards to 6 miles wide. In addition, occasional temporary preventive quarantine areas or temporary buffer zones are placed in other locations as needed.
In spite of some public comments that disagreed with and even criticized a plan to decrease the number of Nilgai antelope in the Boca Chica Beach and surrounding areas south and east of Brownsville, Texas, the latest environmental assessment clears the way for APHIS wildlife services and the U.S. Fish and Wildlife Service (FWS) to deploy the plan, which includes aerial tracking and removal of animals through hunting, with the intent of reducing free-ranging antelope of undetermined numbers from an area where the animals are heavily infected with cattle fever ticks.
Nilgai antelope were first introduced into Texas in the 1940s and are the most abundant free-ranging exotic ungulate in the area with population estimates of more than 36,000 within the state. Nilgai populations are highly mobile and can shift home ranges under pressure. They are large animals; males weigh more than 600 pounds, and easily compete with cattle and native deer.
In February 2007, APHIS Mounted Patrol Inspectors (MPI) received a harvested nilgai antelope that had trailed from privately-owned land to U.S. Fish and Wildlife Service (FWS) property at Boca Chica Beach. APHIS personnel inspected the animal and found it was infested with southern cattle ticks. This finding required APHIS to impose an “exposed” quarantine on the FWS property and an “infested” quarantine on the premises from where the animal had trailed.
In March 2009, after cattle fever tick infestations were found on nearly 25 percent of the nilgai antelope that were harvested from the FWS property of Boca Chica Beach, the quarantine status for the FWS property was changed to “infested.”
The Boca Chica Beach Area consists of approximately 42,000 acres. Approximately 22,400 acres of this area is owned by FWS. In addition to the Boca Chica Beach Area “infested” quarantine status, currently one private premises is quarantined as “infested” immediately adjacent to the Rio Grande, and one of three cattle herds in the area also is quarantined as “infested.” The other two herds remain at risk of infestation.
Texas Animal Health Commission State law requires treatment of all infested animals, including nilgai, present in areas quarantined as “infested.” The increase in ticks in the Boca Chica Beach Area, combined with an increase in the size of the nilgai population (from approximately one dozen nilgai to more than 100 individuals), presents an increased opportunity for the ticks to spread in areas beyond the Boca Chica Beach Area. In May 2014, a cattle fever tick infested premises was discovered across the Brownsville Ship Channel north of the Boca Chica Beach Area. This land mass is owned and managed by the Port of Brownsville, Brownsville Navigational District. Much of this land is leased to private ranchers.
The Bahia Grande Area, also located north of the Ship Channel, is part of the Laguna Atascosa National Wildlife Refuge. This property is 21,700 acres and nearly half of the area consists of wetlands. Bahia Grande is currently quarantined as “exposed.”
Federals officials report an increase in the number of tick infestations during the last several years outside the existing quarantine zone due to several factors, including increased abundance of wildlife along the Texas-Mexico border, increased commingling of livestock with tick-bearing wildlife, and unrestrained movement of wildlife.
To prevent movement of nilgai and the potential spread of cattle fever ticks beyond the Brownsville Navigation District, Boca Chica Beach Area, and Bahia Grande Area, APHIS proposes to conduct aerial harvesting in the Boca Chica Beach Area and aerial harvesting followed by surveillance and ground harvesting in the Brownsville Navigation District and Bahia Grande Area of Cameron County to begin as soon as possible in an effort to protect wildlife during the upcoming bird migration season.