Rocky Mountain spotted fever, a serious illness transmitted by brown dog ticks with a mortality rate of 5 to 10%, has been on the rise in recent years. Evidence suggests that the rise in cases is associated with a steadily increasing global average surface temperature, leading to an expansion of the tick’s habitable region. Now, there is also new growing research suggesting that warmer climates additionally lead to a change in host preference from dogs to humans.
Laura Backus and her team at the University of California Davis, School of Veterinary Medicine reported their findings on tick preference in warmer climates at the Annual Meeting of the American Society of Tropical Medicine and Hygiene. Their experiments used two distinct groups within the Rhipicephalus sanguineus tick species: one tropical species from Arizona and one temperate weather species from Oklahoma. The researchers compared the behaviors of both tick species at two temperatures, 23℃ (74℉) and 38℃ (100℉), by placing ticks in the center of a tube system with a dog on one end and a human on the other. In the high temperature trials, both tick species were twice as likely to prefer humans as compared to those in the low temperature trials.
This behavioral selection preference is hypothesized to be from temperature changes in chemical receptors that alter the ticks’ underlying host preference. Selection of humans over dogs will likely become increasingly prevalent with increasing surface temperatures, leading to more cases of Rocky Mountain spotted fever. Modeled climate change predictions, depicting a rise in temperature across latitudes, can have implications for a variety of disease vectors, not just ticks. The public health implications of climate change are still being investigated, but understanding how disease vectors such as ticks respond to warming temperatures is the first step towards the preventative public health initiatives needed.
Laura Backus is a current PhD student in the Designated Emphasis in The Biology of Vector-Borne Disease in the Departments of Entomology and Nematology and Plant Pathology at the University of California, Davis.
Managing Correspondent: Samantha Tracy
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