The Potential Distribution of the Tick-borne Relapsing Fever Spirochete Borrelia hermsii and vector Ornithodoros hermsi in Western North America
An ecological niche model was created using the Maximum Entropy Species Distribution Model (Maxent) to estimate the probability of the predicted distribution of Ornithodoros hermsi, the soft tick vector for the relapsing fever spirochete Borrelia hermsii. The preference of coniferous forest habitats at a range of higher elevations and the preferred hosts for these ticks has been recognized for many years; however, the climatic factors driving the distribution are not well understood. Here we show that five climate variables combined contributed more than 75% to predicting the distribution of O. hermsi. Temperature extremes accounted for four of the five most important variables. Minimum temperature during the coldest month, mean temperature of the wettest month, maximum temperature during the warmest month and annual temperature range all contributed equally to the model. Predicted shifts in distribution of the tick were examined using climate change models for the year 2050. The geographic distributions with the highest probabilities of tick occurrence were predicted to decrease in all models for the year 2050.