Whereas cases of RMSF associated with brown dog tick transmission were not conclusively identified in the United States until 2005 (3), medical reports of a lethal illness described as a petechial rash and malignant scarlet fever in Mexico date back to 1903 (4). In 1943, epidemiologists identified this illness as the same RMSF that had been discovered in the United States around the turn of the 20th Century (5,6). They described the clinical manifestations and epidemiology of the disease and experimentally confirmed the association with brown dog ticks. Experimental studies in previous publications showed brown dog ticks were an efficient vector of R. rickettsii through 2 generations before this epidemiologic linkage (7). During 1918–1943, medical records indicate that >200 cases of RMSF occurred throughout Mexico, often clustered in neighborhoods or within households (4). The case clustering is a frequently observed characteristic of brown dog tick–associated RMSF transmission because the tick lives in and around human dwellings to be near its preferred host, domesticated dogs. A reduction in cases was reported after the 1940s, and whereas the reason for the decline is unknown, there is a possible connection with high use of DDT to control malaria in endemic regions throughout Mexico and the United States (8). However, RMSF has resurged in northern Mexico; 1,394 cases and 247 deaths were reported during 2003–2016, and the case-fatality rate was 18%, higher than previously seen (4,9). The resurgence of RMSF in Mexico has been particularly evident in the states of Sonora and Baja California but includes many border states in the northern part of the country, such as Chihuahua, Coahuila, and Nuevo Leon (10–14).

RMSF was historically rare in Arizona, consisting of only sporadic cases primarily associated with travel to endemic areas, until September 2003, when a fatal case occurred in an infant with no history of travel outside of their Indigenous Nation (3,15). During the investigation, 16 additional cases were identified in the original community and a neighboring Indigenous Nation; the earliest recognized case had occurred in 2002 (3). The typical vectors, Dermacentor andersoni or D. variabilis ticks, were absent, but many brown dog ticks on dogs secured on the property, free-roaming, and in the peridomestic environment were found. Of the brown dog ticks tested, 3% were positive for R. rickettsii (3). Implementation of intensive prevention measures reduced tick populations and temporarily halted cases. RMSF became endemic in the 2 communities, averaging 5–10 cases per year, with a case-fatality rate of ≈11% (16). During 2009–2011, cases of RMSF were confirmed on 4 other Indigenous Nations in Arizona. Those additional communities rapidly implemented prevention measures and have been able to reduce or eliminate additional human cases of RMSF to date.

Brown dog tick–associated RMSF emergence has historically been met with reactionary public health action, such as increased surveillance and intervention occurring after human cases are identified. However, evidence of R. rickettsii circulation in a zoonotic cycle before human cases were identified has been documented in countries including Brazil (17,18), Panama (19), and Costa Rica (20,21), suggesting early intervention could prevent the spread of RMSF to the human population. Within the United States, conditions for RMSF emergence are already present in some communities. A recent study found R. rickettsii in 1 of 10 adult and 1 of 20 larval brown dog ticks tested from Palm Beach, Florida, USA (22), where this tick species has not been reported to spread RMSF to date. In regions across the globe with similar suitable climates (i.e., 20°C–35°C and relative humidity 35%–95%) (23), if brown dog ticks carrying R. rickettsii were to infest free-roaming dogs or those with limited access to veterinary care, local circulation could follow and lead to outbreaks within the human population.

Local public health agencies should remain vigilant in monitoring for RMSF transmission, especially in regions with a suitable climate for brown dog ticks, large populations of free-roaming dogs, and limited access to medical and veterinary services. Identifying areas of high risk for brown dog tick–associated RMSF is necessary because mitigation efforts are expensive in terms of financial and human resource investment. Developing a conceptual framework for RMSF prevention can aid in identifying communities of high risk and implementing an early warning system that incorporates acarological surveillance. This early warning will increase preparedness and protect human lives while ensuring limited resources are appropriately allocated. This framework requires a One Health approach with expertise from medical, veterinary, and vector control professionals within each community (9,24,25).

Figure 1

Figure 1. Community risk assessment for brown dog tick–associated RMSF. Communities with free-roaming dogs, high levels of brown dog ticks, and Rickettsia rickettsii in the dog or tick population are considered medium...

Preventing RMSF from emerging in a community at risk is necessary because it is difficult to eliminate the disease once it becomes endemic. We have provided a basic framework of risk factors (Figure 1) and outlined the indicators and action items established by an Arizona state interdisciplinary coalition, which is currently in use by Arizona communities, to assess the risk for brown dog tick–associated RMSF (Table). We believe that if a community has free-roaming dogs, high levels of brown dog ticks, and inadequate medical and veterinary care, there is a medium risk for emergence of RMSF. If R. rickettsii is established in the tick or dog population and there are gaps in community understanding and application of tickborne disease prevention, gaps in healthcare worker knowledge of RMSF diagnosis and treatment, or a combination of any of those factors, there is a high risk for emergence. Communities without free-roaming dogs and without high levels of brown dog ticks are considered low risk.

Figure 2

Figure 2. Recommended goals and activities for community-based prevention of brown dog tick–associated RMSF on the basis of the risk assessment road map for medium- or high-risk communities (Figure 1). KAP, knowledge,...

Once leaders of a community have assessed its risk level, they should identify key stakeholders within their network and develop an action plan to address those risk factors and implement RMSF prevention before human cases occur (Table; Figure 2). Implementing an early warning system for rickettsial diseases can prevent illness and death among the human and canine populations and prevent high medical and indirect costs associated with RMSF (25,26). Activities to include in the action plan range from lower cost and effort, such as implementing standard operating procedures for identifying cases of RMSF in clinical settings, to high cost and effort, such as developing and maintaining a vector control program; feasibility and cost may depend on location and infrastructure. Communities should consider individual needs and resources to determine the level of RMSF risk response.

During the emergence of RMSF in Arizona, 5 core functions were identified as critical to prevent and control RMSF: 1) health care system coordination and public health reporting; 2) community education and outreach; 3) animal control and veterinary programs; 4) environmental tick control and surveillance; and 5) finance and budget. Increasing awareness of RMSF symptoms and treatment in the healthcare system and community might be among the most cost-effective interventions available to reduce RMSF illness and death because the bulk of the cost would be personnel time. However, interventions at the animal and environmental level are crucial to reducing tick populations and the potential for disease transmission.

Emerging infectious diseases, which are pathogens that have newly appeared, reappeared, or are rapidly increasing in incidence or range, are a global threat of high public health importance. More than 60% of emerging human diseases are zoonotic (42), affecting humans and animals alike. The effect of vectorborne zoonotic diseases on human health outpaces many other infectious diseases, warranting consideration of new and creative prevention and mitigation strategies (43). Whereas we cannot predict the specifics of an individual disease emerging, vectorborne zoonotic diseases such as RMSF will continue to emerge and are likely to expand in range, especially in the light of land-use and climate changes. Understanding the key transmission drivers and mitigation strategies is imperative to identifying high-risk areas of emergence and rapidly responding to protect human and animal health.

Certain factors associated with climate change, including increases in vector range and abundance, increases in wildlife and human interaction because of land use changes, and pathogen host shifting, are especially relevant to emerging vectorborne zoonotic diseases. The effect of climate change related temperature increases on brown dog tick range and density is unclear because the peridomestic tick can be present in high abundance year-round in some parts of the world. However, previous studies suggest the risk for humans being bit and contracting a disease from brown dog ticks may increase with higher temperatures (44,45). The resistance of this tick species to low humidities, high temperatures, and other environmental conditions that are considered unsuitable for most tick species is remarkable and will likely exacerbate challenges to control brown dog ticks as changes to climates continue (23,45,46).

Brown dog tick–associated RMSF is an emerging public health concern that can be prevented through proper assessment and action. Often it is unclear a community is at risk for endemic RMSF transmission until the first fatal human case occurs; however, there are clear instances when canine cases precede human cases, which demonstrates that preparedness and early detection before human cases are identified may save lives (39). The complexities of the RMSF transmission cycle indicate that the pathogen and risk are not likely to disappear any time soon. Maintaining vigilance and implementing integrated pest management strategies, including routine veterinary care and application of acaricides, in accordance with community risk level is crucial (25,47). The efforts to reduce tick populations and risk for RMSF transmission are cost- and labor-intensive endeavors that might prove unsustainable, especially in communities where access to resources are already restricted. Therefore, it is necessary to explore additional tools to add to the RMSF prevention toolbox, including novel prevention activities that are both scalable and sustainable, such as canine vaccine candidates against R. rickettsii or the brown dog tick itself (48). A vaccine might contribute greatly to reducing tick burdens on dogs or reduce the spread of R. rickettsii throughout the community.

Because of the interrelatedness of canine and human health regarding brown dog tick–associated RMSF, this complex One Health issue requires a communitywide multidisciplinary approach to reducing risk for disease in human and dog populations. Furthermore, the role of brown dog ticks in RMSF transmission is highly correlated with poverty and other social vulnerabilities, bringing health equity into focus (4,14,49–51). Most communities with endemic brown dog tick–associated RMSF are veterinary deserts with little or no access to care in the immediate area, which requires pet owners to travel long distances to seek veterinary care. In addition, many such communities in the United States are also in areas with limited access to medical care because of the rural nature of the environment. Increasing healthcare and veterinary services and accessibility in low-income settings are crucial goals to address health equity issues, including reducing RMSF risk. Until those goals can be realized, medium- and high-risk communities much establish realistic and scalable responses to help reduce RMSF risk on the basis of their resources and infrastructure abilities, such as ensuring human and animal healthcare providers are up to date in recognizing and treating this deadly disease.