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As many as two-thirds of patients with babesiosis experience concurrent Lyme disease, and one-third experience concurrent HGA. infections remain asymptomatic. Additionally, babesiosis was only reportable for surveillance in 31 states in 2014.2 Distribution of vector-borne disease is determined by complex demographic, environmental, and social factors. For many vector-borne diseases, climate change and warming temperatures make transmission seasons longer or more intense or spread vectors so that disease can emerge in different geographic locations. Expanding deer and tick populations, swelling human population density, urbanization and deforestation, and human activities and recreation in wooded areas with exposure to ticks are surmised to relate to this increasing incidence. Most patients acquire babesiosis, HME, and HGA between May and September with reported spikes in June and July.3,6,7 Approximately 75% of cases of babesiosis are diagnosed from June through August.3 Age groups with high incidence for these 3 diseases are similar; the ranges include persons aged 60 to 69 years, 60 to 64 years, and ≥65 years and older for babesiosis, ehrlichiosis,6 and anaplasmosis, respectively.2,7

Cases

0  ■ 1-5  ■ 6-10  ■ 11-20  ■ >20  ■ Not reportable

FIGURE 3. Number of reported cases of babesiosis by US county of residence, 2014.

Geography DC

Cases per million

NN 

0  ■ 0.1-0.7  ■ 0.7-3.1  ■ 3.1-136

FIGURE 4. Incidence of anaplasmosis by region in the US, 2010.

DC

Coinfection

As many as two-thirds of patients with babesiosis experience concurrent Lyme disease, and one-third experience concurrent HGA.3 One study demonstrated that the frequency of

Cases per million

NN 

0  ■ 0.03-1.0  ■ 1.0-3.3  ■ 3.3-26

FIGURE 5. Incidence of ehrlichiosis by region in the US, 2010.

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MAPS COURTESY OF THE US CENTERS FOR DISEASE CONTROL AND PREVENTION

The CDC reports that 90% of cases of babesiosis and anaplasmosis occur in only 7 states with concentrations in the Northeast (Massachusetts, Connecticut, Rhode Island, NewYork, and New Jersey) and the upper Midwest (Minnesota and Wisconsin).2,3,7 In the Northeast, babesiosis occurs in both inland and coastal areas (ie, Nantucket and Martha’s Vineyard in Massachusetts; Block Island in Rhode Island; and Shelter Island, Fire Island, and eastern Long Island in New York) (Figures 3 and 4). This also corresponds to the known geographic distribution of Lyme disease as all of these diseases share the same Ixodes tick vector. HME is most frequently reported in the Southeastern, South Central, and Mid-Atlantic regions of the United States. Approximately 35% of infections of E chaffeensis were reported in Oklahoma, Missouri, and Arkansas in 20105 (Figure 5). Of note, from 2009 to 2011 a novel Ehrlichia species closely related to E muris in Europe and Asia was identified among patients in the upper Midwest (Wisconsin and Minnesota).4 Since then, more than 67 cases have been identified.6 This epidemiologic shift is important as ehrlichiosis had not been previously described in that geographic area and studies suggest that the tick vector has expanded to include I scapularis.4

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