Repellent-treated clothing reduces tick bites by 80 percent, study finds
April 17, 2014
People who work outdoors are at high risk for tick-borne diseases.
The National Institute for Occupational Safety and Health (NIOSH) offers excellent recommendations for people who work outdoors to avoid tick bites – including wearing long sleeves and long pants, tucking pants into boots or socks, spraying your skin and clothing with repellent, and checking yourself regularly for ticks.
It happens, however, that the most vulnerable people – forestry workers, for instance – don’t or can’t comply all the time.
Meagan Vaughn, PhD, recent alumna of the epidemiology program at UNC Gillings School of Global Public Health, wanted to help. She and mentor Steven Meshnick, MD, PhD, epidemiology professor at the Gillings School, conducted a randomized double-blinded trial to determine whether clothing treated with a long-lasting tick repellent could protect outdoor workers in North Carolina from ticks.
Study participants were employees of the N.C. Forest Service, N.C. Division of Parks and Recreation, and N.C. Wildlife Resources Commission. Their uniforms were impregnated with permethrin by InsectShield, a company based in Greensboro, N.C.
Between March 2011 and September 2012, Vaughn and colleagues asked 159 workers to submit their uniforms, hats and socks to be treated (or not treated) with factory-applied permethrin. As participants were not told whether their uniforms had been treated until the end of the study, all were asked to continue using their usual tick-bite prevention methods.
After the study was unblinded, a marked reduction in the number of bites was found in the workers wearing treated uniforms. Participants in the control group logged 780 tick bites during the two spring-to-fall seasons, as compared with 265 in the treatment group. Before the study, both control and treatment group members reported getting about the same number of tick bites, about 19 attached ticks each year, confirming that the reduction was due to the treatment.
During the first year, the treated uniforms reduced tick bites by more than 80 percent, even when subjects in both groups employed their usual tick-bite prevention measures. The treated clothing also significantly reduced the risk of chigger bites and curbed the frequency of mosquito bites. The clothing also protected, but less well, in year 2.
In 2011, more than 39,000 cases of tick-borne disease were reported in the U.S., a far smaller number than the actual incidence of illness related to tick bites. Recently the Centers for Disease Control and Prevention estimated that approximately 300,000 cases of Lyme disease are diagnosed each year in the U.S. Outdoor workers are at particular risk for repeated exposure to tick-borne pathogens. A recent survey of National Park Service employees, for instance, found that 22 percent had antibodies to bacteria that cause Rocky Mountain spotted fever and other illnesses caused by rickettsiae (spotted fever) bacteria.
Vaughn’s study – the first to examine effectiveness of long-lasting permethrin impregnated clothing over an extended period of time – provides important evidence to validate the use of such clothing to protect those who work outdoors in areas where tick bites are likely.
“Tick-borne diseases and other vector-borne diseases are growing threats to human health here in North Carolina and around the world,” Vaughn said. “Since there aren’t vaccines for many of these diseases, personal protection measures are the best tools we have for prevention, particularly for high-risk populations such as outdoor workers. Factory-based treatment of clothing with long-lasting permethrin provides an effective and user-friendly option for tick bite prevention that is as simple as getting dressed.”
UNC co-authors of the study, in addition to Vaughn and Meshnick, include Sheana Whelan Funkhouser, DNSc, epidemiology researcher, Feng-Chang Lin, PhD, research assistant professor of biostatistics; Jason Fine, ScD, professor of biostatistics, all in the Gillings School, and Jonathan J. Juliano, MD, assistant professor of medicine in the School of Medicine’s Division of Infectious Diseases. Charles Apperson, PhD, William Neal Reynolds Distinguished Professor Emeritus of entomology at N.C. State University, also is co-author. Fine also holds a professorship of statistics and operations research in UNC’s College of Arts and Sciences.
The article “Long-lasting permethrin-impregnated uniforms: A randomized-controlled trial for tick bite prevention,” was published online April 16 in the American Journal of Preventive Medicine.