New Study Points to Management Strategies for Invasive Tick on Cattle Farms
By Andrew Porterfield
The Asian longhorned tick (Haemaphysalis longicornis) joins a long line of invasive arthropods in North America, this one discovered on a New Jersey sheep farm in 2017. While not a significant threat to humans—it does not spread Lyme disease, though it has been found carrying the Rocky Mountain spotted fever pathogen Rickettsia rickettsii— H. longicornis has been deadly to livestock, particularly cattle.
Since its first North American discovery in 2017, Haemaphysalis longicornis has spread to 18 other eastern and Midwestern states as of April 2023. It can spread quickly because of its parthenogenic reproduction (i.e., female reproduction without mating), rapid population growth, and ability to feed on multiple hosts. It is a particular problem for the cattle industry, because it is a vector of Theileria orientalis Ikeda, a protozoan that infects red and white blood cells and causes anemia in cattle. Severe infestations have occurred on individual animals, and can sometimes kill the animal due to blood loss and anemia. There is no approved treatment.
Control, then, focuses on preventing the tick and its accompanying parasite from entering cattle ranches. Management methods include checking livestock and farms for ticks and using acaricides. (Currently, only permethrins are permitted for livestock facilities in the United States.)
But it’s still uncertain which tick management practices, and combinations thereof, work the best at preventing H. longicornis infestations. Researchers in Tennessee studied three cow-calf farms in the state from 2019 to 2021 to determine which of three management strategies was most effective. Their results, believed to be the first on-farm field studies of H. longicornis, were published in September in the Journal of Medical Entomology.
Rebecca Trout Fryxell, Ph.D., assistant professor of veterinary and medical entomology, and postdoctoral researcher Rebecca A. Butler, Ph.D., both in the Entomology and Plant Pathology Department at the University of Tennessee, Knoxville, worked with three cattle farms in their study. After providing the owners of each farm with information on tick control from the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS), they allowed them to devise their own tick management strategy:
- Farm 1 kept a closed herd of 17 cows (no animals brought in from outside the farm), cut brush monthly, used on-animal acaricides, and allowed the researchers to drag for ticks each week using a 2-by-3-foot corduroy drag cloth.
- Farm 2 kept an open herd of 50 cows, cut brush once yearly, did not use acaricides, and allowed for monthly tick dragging.
- Farm 3 kept an open herd of 35 cows, cut brush once yearly, used acaricides, and allowed for monthly tick dragging.
At the end of the three-year study, the researchers found that Farm 1 reduced tick presence by 90 percent. Tick collections fell from approximately 5,000 in the first year to just 12 H. longicornis ticks two years later. Farm 3 also saw significant reductions in tick populations; a 68 percent decrease from 2020 to 2021. Farm 2 saw no relationship between tick presence and applied treatments.
The degree of tick reduction was a surprise to the researchers, says Butler. “We even increased the number of transects on Farm 1 and still were not finding H. longicornis,” she says.
From this study, it appeared that the combination of closed herds, acaricides, and monthly brush cutting (as well as more frequent monitoring via dragging) was the better strategy for tick prevention. But every farm could be very different, Trout Fryxell cautions.
“We need to study this further because it was only three farms, and successful management could have been related to something we didn’t investigate,” she says. “A lot of producers don’t have the ability to work their animals like others do. We hope to monitor many producer decisions over time and those effects on tick populations.”
And, are 12 ticks (even if down from 5,000) still 12 too many, considering their likelihood of transmitting pathogens? It depends, Trout Fryxell and Butler say.
“Producers’ tolerance to ticks should be further investigated. Unfortunately, many farmers don’t ‘notice’ ticks on their animals because the larvae and nymphs are so small and often blend in with their fur,” Butler says.
“We can think of this as what animals can tolerate and what producers will tolerate. Many have tolerated ticks for years,” Trout Fryxell says.
Journal of Medical Entomology
Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.