 In the early 1940s, outbreaks were described in the Mexican states of Sinaloa, Sonora, Durango, and Coahuila driven by dogs and "Rhipicephalus sanguineus" sensu lato, the brown dog tick.Over the ensuing 100 years case fatality rates were 30%–80%.In 2015, there was an abrupt rise in Sonora cases with 80 fatal cases.