A wolf at the door: the ecology, epidemiology, and emergence of community- and urban-level Rocky Mountain spotted fever in the Americas.

RMSF, a tickborne infection caused by Rickettsia rickettsii, produces severe and fatal disease in humans and dogs. Since the beginning of the 21st century, cases have risen dramatically, most notably in Mexico and Brazil, where outbreaks occur in urban centers including cities with populations of > 1,000,000 persons. Reported case fatality rates can exceed 50%. Factors consistent with high case fatality include lack of awareness of disease ecology, limited capacity for diagnosis, and delay in appropriate antimicrobial treatment. The emergence of urban hyperendemic foci has been leveraged by 2 distinct but similar anthropogenic events that create disproportionately high numbers of vertebrate amplifiers of R rickettsii, as well as the tick species that transmit this pathogen in proximity with dense human populations. This often occurs in neighborhoods with a highly marginalized at-risk population that includes persons in poverty and particularly children, and health management systems that are under-resourced. We discuss strategies to reduce host dog populations, particularly in Mexico, and capybaras in Brazil. We review challenges to the control of tick populations in these settings. Robust systems are required to enhance awareness of RMSF among medical practitioners and people at risk of RMSF. Public health campaigns should incorporate innovative behavioral science (eg, diverse learning models, motivational interviews, and gamification) to increase prevention and understanding within communities. While anti-Rickettsia or anti-tick vaccines will be necessary to resolve this One Health crisis, impactful implementation will require data-driven and multiple-target innovations to address challenges with hosts, ticks, medical systems, and public welfare. The companion Currents in One Health by Foley, Backus, and López-Pérez, JAVMA, March 2025, addresses helpful information for the practicing veterinarian.