UNIVERSITY PARK, Pa. — The spread of the blacklegged tick, the primary vector for the pathogen that causes Lyme disease, may be facilitated in Pennsylvania by animals that people rarely associate with it — black bears, according to researchers in Penn State's College of Agricultural Sciences.
In a recently published study, the researchers reported on the presence, abundance and spatial distribution of ticks on black bears, with an eye toward better understanding the bears' role in tick ecology and dispersal and improving on-host surveillance techniques for ticks.
"American black bear populations in the Northeast have been rising substantially since the 1980s," said lead researcher Hannah Tiffin, dual-title doctoral degree candidate in entomology and in international agriculture and development. "Pennsylvania has seen a dramatic increase in bear numbers, with the estimated population doubling between the late 1980s and 2001 and continuing to rise in the last 20 years."
During roughly the same time frame, she noted, tick-borne diseases in humans have risen significantly, with the number of cases reported to the U.S. Centers for Disease Control and Prevention nearly tripling between 2004 and 2017. Lyme disease, which is caused by the bacterium Borrelia burgdorferi and is transmitted primarily by the blacklegged tick (Ixodes scapularis), is the most frequently reported vector-borne disease in the United States. Pennsylvania leads the nation in reported Lyme cases.
"To date, most wildlife studies of blacklegged ticks have looked at two species — the white-tailed deer and the white-footed mouse," Tiffin said. "As a result, there's a lack of research on other animal species in terms of their role in tick dispersal, their suitability as hosts and their status as reservoirs of disease pathogens."
In addition, standardized tick-surveillance methods have not been developed for host species that rarely are studied for tick burden and parasitism, explained study co-author Erika Machtinger, assistant professor of entomology, who directs the college's Veterinary Entomology Laboratory.
"Studies of ticks on wild mammals other than white-tailed deer and white-footed mice usually consist of opportunistic tick collections," Machtinger said. "For instance, most previous studies of tick parasitism of black bears consisted of opportunistic collections on nuisance bears or bears killed by vehicle collisions or by hunters, which limits observations to specific times of the year.
"Because black bears are known to host several species of ticks and these animals can travel long distances — particularly male bears that may travel more than 100 miles when establishing a new territory — it's important to understand their role in tick ecology and dispersal, especially in a region with high numbers of Lyme disease cases."