New research presented at the Annual Meeting of the American Society of Tropical Medicine and Hygiene warns that climate change may increase the risk of humans contracting tick-borne diseases. This video from Live Science summarizes the study, which was led by Laura Backus—MPH and DVM at the University of California, Davis School of Veterinary Medicine. In a statement to Eureka Alert, Backus said, "we found that when temperatures rose from about 74 to 100 degrees Fahrenheit, brown dog ticks that carry the disease were 2.5 times more likely to prefer humans over dogs."
Backus also told Eureka Alert that earlier work suggested that brown dog ticks might be more aggressive toward humans in higher temperatures. The team aimed to understand how rising temperatures might elevate humans' risk of contracting tick-borne illnesses such as Rocky Mountain spotted fever (RMSF). Eureka Alert reports that occurrences of RMSF and related tick-borne diseases have "risen dramatically" through the past 20 years. RMSF is of particular concern due to a high fatality rate that can exceed 20%.
To assess the risk, the team conducted a series of tests using one human and one dog in separate large wooden boxes connected by a clear plastic tube containing ticks. As clarified in the video, the plastic tube had barriers at each end to protect the subjects. According to Eureka Alert, during 20-minute intervals, the researchers observed which host the ticks preferred at both 74 degrees Fahrenheit and 100 degrees Fahrenheit.
Backus reported to Eureka Alert that the tropical lineage tick was markedly decisive in targeting humans at the higher temperature. This species of brown dog tick lives throughout warm, southern regions of the United States. However, Backus expects that as climate change increases temperatures across the nation, this species will likely move northward into other areas.
The study also tested the temperate lineage ticks, which are currently found throughout the continental United States and can be carriers of RMSF. While this brown dog tick species showed a slight preference for humans, they showed a "pronounced decrease in their preference for dogs." Backus believes that this means that "hot temperatures may also elevate risks of RMSF in areas where the temperate ticks are more common."
According to Eureka Alert and Backus's statements, this research is essential to health officials to prepare them for increased instances of RMSF and other tick-borne illnesses.