Survey of Western Black-Legged Ticks and Lyme Disease in Utah
51 locations were surveyed in 2011 for western
black-legged tick to determine if the Lyme disease-
causing bacteria, Borrelia burgdorferi, occurs in Utah.
The red markers above indicate sites where ticks were
found and blue markers indicate sites without tick
Lyme was not detected within any of the 41 western
black-legged ticks that were collected. The survey will
continue in 2012.
Lyme disease is the number one tick-vectored disease in the United States, especially in the Northeast, upper Midwest states, and Pacific Coast states. Its known prevalence in the Rocky Mountain region is limited to Colorado and Arizona; however the probability of human contraction in these states is considered low. There are no confirmed cases of Lyme disease originating in Utah; however, further investigation is needed to resolve the question: Does Lyme occur in Utah? Detecting Lyme in Utah would help inform the medical community of the presence of the disease, allowing clinicians to make informed, timely diagnoses and treatments.
In 2010, 36 residents from Lehi were associated with a potential Lyme disease cluster (UT Department of Epidemiology, 2010), prompting the Utah County Health Department and the Utah Department of Health to form a task force to examine the cases. To date, none of the people associated with this cluster have been shown to have contracted Lyme in Utah. As part of the task force, Utah State University researchers Ryan Davis, Scott Bernhardt, and Ricardo Ramirez sought to determine the prevalence of the Lyme disease-causing bacteria, Borrelia burgdorferi (Lyme), and its tick vector, the western black-legged tick (WBLT) (Ixodes pacificus), by collecting and testing ticks for the presence or absence of Lyme.
In 2011, 51 sites in Utah, Tooele, Juab, Iron, and Washington counties were surveyed between May and July, and October and November. Sites were selected using historical tick collection data, public input, information from the Centers for Disease Control, tick-host distribution maps, and vegetation typing. At each collection site, we recorded weather conditions, temperature, elevation, aspect, GPS coordinates, photographs, and vegetation description.
We sampled for ticks using a square felt cloth dragged over vegetation. Ticks were found at 7 of the 51 sites. In total, we 78 adult ticks–41 Ixodes (WBLT) and 37 Dermacentor (Rocky Mountain wood tick, winter tick, and “Rocky Mountain sheep tick”)–and 57 Dermacentor larvae were collected. WBLT were found at 3 sites and Dermacentor ticks were found on 5 sites, some sites yielding both tick genera.
All ticks were DNA-tested (using PCR) for the presence of Lyme, and all tested negative.
As documented from prior tick surveys in Utah, WBLT is one of the more commonly encountered tick species behind Rocky Mountain wood tick and other ticks in the genus Dermacentor. WBLT prefer arid habitats associated with basin-and-range mountains. Ticks collected during our survey were found on south- to southeast-facing slopes at elevations between 5,600 and 7,000 feet, and when temperatures ranged from 43°F to 60°F. Preferred tick habitat included Gambel oak, juniper, sage, and small grass communities. Gambel oak was a major indicator of WBLT habitat and black sage appeared to be a favorite of WBLT adults and Rocky Mountain wood tick larvae in the fall.
Adult ticks that are frequently encountered in Utah
are the western black-legged tick (Ixodes pacificus)
(female, top left and male, top right) and Rocky Mt.
wood tick (Dermacentor andersoni)
(female, bottom left and male, bottom right).
Ticks are collected using a standard flannel tick drag.
Western black-legged ticks were most commonly
collected on dry sites with gamble oak, juniper, sage,
and small grasses.
While we did not detect Lyme in this survey, we believe that Utah’s long winters and hot, dry summers affect the WBLT life cycle, limiting the spread of Lyme between tick and host. This means that if Lyme does occur in the state, it would occur infrequently and pose minimal threat to humans. In California, where the transmission of Lyme disease from infected ticks to humans is well documented, only about 5% or less of the WBLT population has been shown to carry Lyme. In Utah, there are no confirmed cases of Lyme originating in the state, indicating that the number of WBLTs carrying Lyme is likely to be even lower than in CA. Because of this, we will need to test a large number of WBLT to determine whether Lyme occurs in Utah.
Until we can issue conclusive results, care should be taken to avoid tick habitat in early spring and late fall. The most commonly encountered tick in Utah is the Rocky Mountain wood tick and it is capable of transmitting other diseases besides Lyme, such as: Rocky Mountain spotted fever, Colorado tick fever, and tularemia (rare).
After spending time outdoors, always conduct a thorough tick inspection. Disease transmission usually takes over 24 hours of tick attachment. Removing ticks within a day will greatly reduce the odds of contracting any tick-borne illness. For more information on tick-borne diseases and proper tick removal, please see a previous article: Ticks and Associated Diseases Occurring in Utah.
If you find a tick in Utah, please send it to the Utah Plant Pest Diagnostic Lab to help us to increase our sample size for Lyme detection. Ticks should be placed in ethyl alcohol or rubbing alcohol with a notation of the date, time, and location of the collection. Please include a UPPDL sample submission form with your contact information (no fee).
A summary of our survey and the complete results, including site pictures, can be found here. This project is funded by grants from USU Extension, the Centers for Disease Control, and the Utah Bureau of Epidemiology.
-Ryan Davis, Arthropod Diagnostician