Epidemiology and Spatial Emergence of Anaplasmosis, New York, USA, 2010–2018

Alexis Russell; Melissa Prusinski; Jamie Sommer; Collin O'Connor; Jennifer White; Richard Falco; John Kokas; Vanessa Vinci; Wayne Gall; Keith Tober; Jamie Haight; JoAnne Oliver; Lisa Meehan; Lee Ann Sporn; Dustin Brisson; P. Bryon Backenson


Emerging Infectious Diseases. 2021;27(8):2154-2162. 

In This Article

Abstract and Introduction


Human granulocytic anaplasmosis, a tickborne disease caused by the bacterium Anaplasma phagocytophilum, was first identified during 1994 and is now an emerging public health threat in the United States. New York state (NYS) has experienced a recent increase in the incidence of anaplasmosis. We analyzed human case surveillance and tick surveillance data collected by the NYS Department of Health for spatiotemporal patterns of disease emergence. We describe the epidemiology and growing incidence of anaplasmosis cases reported during 2010–2018. Spatial analysis showed an expanding hot spot of anaplasmosis in the Capital Region, where incidence increased >8-fold. The prevalence of A. phagocytophilum increased greatly within tick populations in the Capital Region over the same period, and entomologic risk factors were correlated with disease incidence at a local level. These results indicate that anaplasmosis is rapidly emerging in a geographically focused area of NYS, likely driven by localized changes in exposure risk.


Anaplasmosis is an emergent tickborne disease caused by the obligate intracellular bacterium Anaplasma phagocytophilum.[1] Initially termed human granulocytic ehrlichiosis, human infection with A. phagocytophilum was first described in 1994 in patients from Minnesota and Wisconsin, USA.[1,2] Now referred to as human granulocytic anaplasmosis or simply anaplasmosis, this infection is characterized by a nonspecific influenza-like illness marked by fever, fatigue, muscle aches, and headache.[3] Although severe complications and death occur in rare instances, most patients recover fully after treatment with appropriate antimicrobial drugs.[4]

Human infection with A. phagocytophilum has now been documented in patients in North America, Europe, and Asia, and a notable incidence has occurred in the United States.[5] Anaplasmosis became a nationally notifiable disease in the United States during 1999, and nationwide case counts have since increased >16-fold, from 348 cases during 2000 to 5,762 cases during 2017.[6] Most of these infections occur in the northeastern and upper midwestern states, where well-established populations of Ixodes scapularis (blacklegged or deer ticks) transmit A. phagocytophilum in addition to the infectious agents of Lyme disease, babesiosis, and Powassan virus disease.[7–9]

New York State (NYS), which is situated within the northeastern United States, to which tickborne diseases are endemic, has reported the second highest number of anaplasmosis cases of any state, closely behind Minnesota.[10–12] Surveillance of anaplasmosis cases by the NYS Department of Health (NYSDOH) indicates that since the first NYS case was reported in 1994, the burden of anaplasmosis has increased substantially, accounting for a larger proportion of NYS tickborne disease cases every year (≈4% during 2010 vs. ≈11% during 2018).[13] Since 2015, anaplasmosis has consistently surpassed babesiosis as the second most common tickborne disease in NYS, after Lyme disease.[13] In addition to surveillance of tickborne disease cases, the NYSDOH also conducts routine vector surveillance to monitor the dynamics of tick populations and the prevalence of tickborne pathogens, including A. phagocytophilum, to estimate tickborne disease risk across the state. We examined human case surveillance and tick surveillance data during 2010–2018 to assess the epidemiology, risk for pathogen exposure, and spatiotemporal emergence patterns of anaplasmosis in NYS.