4 November 2009

5 minute read

North America

The fever tick is a major concern to the livestock and wildlife industry, said Dr. Tom Hairgrove, livestock systems programme coordinator with AgriLife Extension Service and Texas Veterinary Medical Diagnostic Laboratory. It can carry and transmit Babesia, a blood parasite that can kill adult cattle. Other hosts for the fever tick are horses, deer, elk and other deer species.

“The purpose of this summit was to bring together all stakeholders (livestock and wildlife) in Texas to begin a concerted effort in battling movement of the fever tick,” Dr Hairgrove said. “I think at the end of the day, everyone got a sense of where we are at and the work that needs to be done.”

“This is a major concern not just for Texas, but the US,” said Dr. Ron Gill, AgriLife Extension beef cattle programme leader and associate department head for animal science at Texas A&M University. “There needs to be more producer education, research and commercialisation of technology that will all aid in preventing spread of the fever tick. If we can control the spread of the ticks which can carry the protozoa, we can prevent the occurrence of tick fever that had huge consequences in the 1940s and thousands of cattle deaths in the 1800s.”

Dr Gill said if the tick and the disease are not controlled at the South Texas border, “the economic consequences of re-introduction of tick fever into the naive US cattle population would be staggering.”

The fever tick was declared eradicated from the US in 1943, except for a permanent quarantine zone that runs from Del Rio to Brownsville. Earlier this year, Texas Animal Health Commission officials quarantined more than 150,000 acres in Starr and Hildalgo counties. In Zapata County, a five-mile quarantine perimeter was enforced around fever-tick infested pastures, according to animal health officials. Currently, more than 1.4 million acres are under quarantine for ticks and 666 premises involved. Counties involved are Maverick, Dimmit, Webb, Starr, Hildalgo, Zapata, and Jim Hogg, according to the animal health commission.

Potential economic losses due to the cattle tick are in the millions, said Dr. David Anderson, AgriLife Extension Service livestock economist. In one modeling scenario, Dr Anderson said, a widely separated area with diverse cattle operations where the fever tick is found with no disease transmitted, losses would approach $100 million or more when calculating state/producer costs, treatment and eradication efforts.

“That’s assuming there’s one tick found in the outbreak,” Dr Anderson said.

The ticks cling to forage during the warm-season months and wait for a host animal. Ticks have to be at least 6 millimeters in length to be detected. When examined in the chute, cattle have to be physically examined for detection. If cattle ticks are found in a herd, several eradication measures are taken, according to state animal health officials:

- Cattle and pastures are quarantined for nine months or longer.

- Cattle are inspected and run through dipping vats-spray boxes containing acaracide.

- Horses are sprayed and wildlife are provided medicated feed or lured to treatment stations where they can rub against permethrin-coated posts while eating.

Once cattle are declared tick free, the cattle can be moved to another site, allowing the vacated pasture to let the remaining ticks desiccate (die). However, greater success has been to inspect and treat animals every 14 days with acaracide or every 25-28 days with Doramectin, officials said.

Dr. Pete Teel, Texas AgriLife Research entomologist, told attendees there are two cattle fever tick species that were introduced to the New World by early explorers and settlers. B. microplus originated in the Tropics of India and are thought to be distributed from southern Texas along the Gulf Coast to Florida. B. annulatus is thought to have originated from the temperate climate of the Mediterranean and was distributed throughout 14 southern US states.

“The populations of cattle ticks are influenced by the number and diversity of hosts and by weather,” he said. “Cattle are considered the primary hosts. However, the emerging interaction between cattle and wildlife influence the population dynamics of this tick. That’s why shared grazing among these animals is a focal point of concern. Dry weather helps reduce populations through desication of ticks on vegetation, but when rains return, populations start building and increasing as rain persists.”

The survivorship of eggs and larvae is highest in shady places, he said.

“These happen to also be habitats preferred by cattle in the summer,” Teel said. That’s when the potential for ticks to interact with cattle are at their highest as cattle look to escape the heat and seek shady areas.

“Our future challenges are connected to detection, surveillance, population and survivorship,” Teel said. “All of these areas need lots of attention by all of the cattle industry to ensure a large outbreak doesn’t occur.”

Another area of interest is change in land use. Some ranches have switched from cattle operations to hunting operations.

“And even though these cattle have been pulled off of these pastures, wildlife are still there and serve as potential hosts,” said Dr. Bob Hillman, director of the Texas Animal Health Commission.

Another concern is the development of potential products to combat the tick that have not yet been approved for use, Dr Hillman said. He told attendees that federal and state officials need to become more engaged about cattle tick prevention efforts to secure “much-needed funding” for these activities.

“The fever tick is a US problem,” Dr Hillman said. He noted part of the problem with getting federal support for control of the fever tick is the longstanding view that this is just a Texas problem only.

“If we don’t control the tick at the border, this becomes a national problem,” Dr Hillman said.

Dr. Adalberto Perez de Leon, laboratory director with the U.S. Department of Agriculture-Livestock Insects Research Unit in Kerrville, presented research projects currently in progress with wildlife.

A “two-poster system” has been tested where white-tailed deer are drawn to a permethrin–treated feeder. The deer push their head through an opening and during this process, their neck and shoulder region are rubbed with permethrin. The deer then spread the permethrin over the rest of their body through normal grooming.

Another system, which uses Ivomectin-treated corn dispensed in feeders for white-tailed deer, is being used as part of prevention efforts. However, the treated corn must be withdrawn well in advance of hunting season (at least 60 days) due to potential residues in the meat. Both systems were developed by USDA-ARS.

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