Anaplasmosis
Annual Summary of Reportable Diseases

• 75% of anaplasmosis cases with a known onset date reported illness in May, June, or July, consistent with exposures during peak season for blacklegged tick activity in Minnesota
• 32% of cases were hospitalized for their anaplasmosis infection 

In 2023, 508 confirmed and probable cases of anaplasmosis (8.8 cases per 100,000) were reported, slightly down from the 540 cases reported in 2022. Although case numbers have been declining over the last few years, the 2023 total is maintaining the trend seen through the mid-2010s. A median of 603 cases per year have been reported since 2010 (Figure: Anaplasmosis Case Counts (2010-2023)). In 2023, 319 (63%) confirmed and probable cases reported were male. The median age for cases was 66 years (range, 1 to 98), 14 years older than the median age of confirmed Lyme disease cases, but equal to the median age of confirmed or probable babesiosis cases (66 years). As is typical, most cases had illness onsets during the summer months, with 75% of 484 cases with a known onset date reporting illness in May, June, or July. This timing is consistent with exposures occurring during the typical peak season for blacklegged tick activity in Minnesota. In 2023, 163 (32%) cases were hospitalized for their anaplasmosis infection, with a median duration of four days (range, 2 to 25 days). Ninety-four (19%) cases reported complications (e.g., organ failure) due to anaplasmosis infection. 

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• Download: 2023 Anaplasmosis Case Counts (CSV)
• Download: 2023 Anaplasmosis Cases by Disease Risk (CSV)
• Download: 2023 Anaplasmosis Cases by Onset Date (CSV)
• Download: 2023 Anaplasmosis Cases by Age Group (CSV)

Anaplasmosis is a rickettsial disease caused by the bacteria Anaplasma phagocytophilum, which is transmitted by bites from Ixodes scapularis, the blacklegged tick. Although the organism that causes anaplasmosis has been known by other names and was once thought to be a part of the genus Ehrlichia, anaplasmosis and ehrlichiosis are distinct diseases caused by different rickettsial species. The same tick vector also transmits the etiologic agents of Lyme disease, babesiosis, ehrlichiosis (due to E. muris), and Powassan virus. In rare circumstances, A. phagocytophilum may be transmitted by blood transfusion. In 2022, 540 confirmed and probable cases of anaplasmosis (9.3 cases per 100,000) were reported, slightly down from the 603 cases reported in 2021. Although case numbers were a bit lower the last few years, the 2022 total is keeping with the trend we saw through the mid2010s. A median of 608 cases per year have been reported since 2010. In 2021, 341 (63%) confirmed and probable cases reported were male. The median age for cases was 65 years (range, 3 to 93), 13 years older than the median age of confirmed Lyme disease cases, but equal to the median age of confirmed or probable babesiosis cases (65 years). As is typical, most cases had illness onsets during the summer months, with 70% of 505 cases with a known onset date reporting illness in May, June, or July. This timing is consistent with exposures occurring during the typical peak season for blacklegged tick activity in Minnesota. In 2021, 173 (29%) cases were hospitalized for their anaplasmosis infection, with a median duration of four days (range, 1 to 55 days). Ninety-eight (18%) cases reported complications (e.g., organ failure) due to anaplasmosis infection.

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Anaplasmosis is a rickettsial disease caused by the bacteria Anaplasma phagocytophilum, which is transmitted by bites from Ixodes scapularis, the blacklegged tick. Although the organism that causes anaplasmosis has been known by other names and was once thought to be a part of the genus Ehrlichia, anaplasmosis and ehrlichiosis are distinct diseases caused by different rickettsial species. The same tick vector also transmits the etiologic agents of Lyme disease, babesiosis, ehrlichiosis (due to E. muris), and Powassan virus. In rare circumstances, A. phagocytophilum may be transmitted by blood transfusion. In 2021, 603 confirmed and probable cases of anaplasmosis (10.5 cases per 100,000) were reported, up from the 407 cases reported in 2019. Although case numbers were a bit lower the last few years, the 2021 total is more in keeping with the trend we saw through the mid2010s. A median of 613 cases per year have reported since 2010 (Figure 1). In 2021, 382 (63%) confirmed and probable cases reported were male. The median age for cases was 64 years (range, 1 to 96), 19 years older than the median age of confirmed Lyme disease cases, but close to the median age of confirmed or probable babesiosis cases (69 years). As is typical, most cases had illness onsets during the summer months, with 66% of cases reporting illness onsets in May, June, or July. This timing is consistent with exposures occurring during the typical peak season for blacklegged tick activity in Minnesota. In 2021, 173 (29%) cases were hospitalized for their anaplasmosis infection, with a median duration of 4 days (range, 1 to 44 days). Forty-seven (8%) cases reported complications (e.g., organ failure) due to anaplasmosis infection

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2020 data is not available.

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Anaplasmosis is a rickettsial disease caused by the disease agent Anaplasma phagocytophilum, which is transmitted by bites from Ixodes scapularis, the blacklegged tick. Although the organism that causes anaplasmosis was previously known by other names and thought to be a part of the genus Ehrlichia, anaplasmosis and ehrlichiosis (due to E. chaffeensis) are distinct diseases caused by different rickettsial species. The same tick vector also transmits the etiologic agents of Lyme disease, babesiosis, ehrlichiosis (due to E. muris), and Powassan virus. In rare circumstances, A. phagocytophilum may be transmitted by blood transfusion.

In 2019, 407 confirmed or probable cases of anaplasmosis (7.2 cases per 100,000) were reported, down from the 496 cases reported in 2018. Despite some annual fluctuations, including a decrease in cases the past 2 years, yearly case totals over time continue to trend upward, with a median of 620 cases reported per year since 2010. In 2019, 245 (60%) confirmed or probable cases reported were male. The median age was 62 years (range, 0 to 92), 14 years older than the median age of confirmed Lyme disease cases, but close to the median age of confirmed or probable babesiosis cases (67). As is typical, most cases had illness onsets during the summer months, with 69% of cases reporting illness onsets in June, July, or August. In 2019, 133 (33%) cases were hospitalized for their anaplasmosis infection, with a median duration of 4 admission days (range, 2 to 374 days). Thirty-three (8%) cases reported complications (e.g., organ failure) due to anaplasmosis infection.

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Anaplasmosis, caused by Anaplasma phagocytophilum, is transmitted by bites from Ixodes scapularis, the blacklegged tick. Although the organism that causes anaplasmosis was previously known by other names and thought to be a part of the genus Ehrlichia, anaplasmosis and ehrlichiosis (due to E. chaffeensis) are distinct diseases caused by different rickettsial species. The same tick vector also transmits the etiologic agents of Lyme disease, babesiosis, ehrlichiosis (due to E. muris), and Powassan virus. In rare circumstances, A. phagocytophilum may be transmitted by blood transfusion.

In 2018, 496 confirmed or probable cases (8.9 cases per 100,000 population) were reported, down from the 638 cases reported in 2017. Despite some annual fluctuations in reported cases, the overall trend is an increase in yearly case totals over time, with a median of 627 cases reported per year since 2010. Sixty-two percent (307) of cases reported were male. The median age of cases was 61 years (range, 2 to 92), 17 years older than the median age of confirmed Lyme disease cases. As is typical, most cases had illness onsets during the summer months, with 72% of cases reporting illness onsets in June and July. In 2018, 132 (27%) cases were hospitalized for their infection, with a median duration of 4 days (range, 2 to 33 days).

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• Archive of Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health
  Archive of past summaries (years prior to 2023 are available as PDFs).