The emergence of tick-borne pathogens depends on ecological opportunity and barriers to persistence within vectors and hosts. Borrelia burgdorferi is well established in the mid-Atlantic, whereas Babesia microti and Anaplasma phagocytophilum remain patchily distributed. Five years of integrated surveillance (2020-2024) at three Maryland sites allowed us to track B. microti and A. phagocytophilum establishment by screening questing Ixodes scapularis nymphs, Peromyscus leucopus-fed nymphs, and P. leucopus samples by qPCR, contextualized with county-level human case data. B. burgdorferi was consistently detected in all sites and sample types, with prevalence generally 5%-20% in questing nymphs and exceeding 30% in hosts, confirming long-term enzootic maintenance. By contrast, B. microti and A. phagocytophilum were initially sporadic but increased in rodents and P. leucopus-fed ticks. Over time, A. phagocytophilum prevalence significantly increased to above 20% in some P. leucopus-fed nymphal collections despite much lower prevalence in questing ticks, highlighting the early-warning value of blood meal-associated surveillance. Notably, B. microti reached very high prevalence in P. leucopus hosts at a specific site (up to ~80%) while remaining rare or absent in questing and engorged nymphs, highlighting a pronounced decoupling between host infection and vector prevalence. Coinfections were rare, though enrichment of B. burgdorferi + A. phagocytophilum in P. leucopus-fed ticks suggests possible facilitation during early establishment. These results indicate that B. microti and A. phagocytophilum are actively emerging in Maryland, following their establishment in the Northeast and Upper Midwest. Combining surveillance from questing nymphs, P. leucopus-fed nymphs, and reservoir hosts provides a framework for detecting enzootic cycles before they appear in questing ticks or human case counts, offering early-warning capacity for public health preparedness.IMPORTANCEUnderstanding why some tick-borne pathogens become ecologically established while others remain sporadic is central to predicting human disease emergence. By combining surveillance of questing nymphal Ixodes scapularis ticks, Peromyscus leucopus-fed nymphal ticks, and Peromyscus leucopus reservoir hosts across 5 years in Maryland, we show that Babesia microti and Anaplasma phagocytophilum remain in the early stages of enzootic establishment, whereas Borrelia burgdorferi is deeply established. This integrated approach demonstrates how pathogen biology within the tick shapes field prevalence and highlights P. leucopus-fed ticks as a powerful xenodiagnostic early-warning tool for detecting emerging pathogens before they are reflected in questing populations or human case data.
Joyner et al. (Mon,) studied this question.
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