Babesiosis
Annual Summary of Reportable Diseases

Babesiosis is a malaria-like illness caused by a protozoan parasite, typically Babesia microti, which infects red blood cells. B. microti is transmitted to humans by bites from Ixodes scapularis (the blacklegged tick), the same vector that transmits the agents of Lyme disease, anaplasmosis, one form of ehrlichiosis, and a strain of Powassan virus. Babesia parasites can also be transmitted by blood transfusion. Although most people infected with Babesia have asymptomatic infections, people with weak immune systems, other co-morbidities, and the elderly can become seriously ill. In 2022, there were 61 confirmed and probable cases reported (1.1 cases per 100,000), a slight decrease from the 63 cases in 2021. Over the past decade, slight annual fluctuations in reported cases have been observed, however, reported case numbers continue to trend upward (range, 41 to 72) and are consistently higher than annual cases reported in the previous decade, 2000-2010 (range, 1 to 56). In recent years, case demographics were similar. In 2022, 37 (61%) of the cases occurred in males. The median case age was 65 years (range, 4 to 87), down slightly from 69 in 2021. This is equal to the median age for anaplasmosis (65 years), but older than the median age for Lyme disease (52 years). Illness onset dates peaked in the summer months: 41 (67%) of the 61 cases with known onset date reported first experiencing symptoms in June, July, or August. Twenty-three (38%) of the 60 cases where hospitalization status was obtained were hospitalized due to their infection in 2022 with a median admission duration of four days (range, 3 to 16). Although fifteen patients reported severe complications (e.g., organ failure), no patients died as a result of their babesiosis infection

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Babesiosis is a malaria-like illness caused by a protozoan parasite, typically Babesia microti, which infects red blood cells. B. microti is transmitted to humans by bites from Ixodes scapularis (the blacklegged tick), the same vector that transmits the agents of Lyme disease, anaplasmosis, one form of ehrlichiosis, and a strain of Powassan virus. Babesia parasites can also be transmitted by blood transfusion. Although most people infected with Babesia have asymptomatic infections, people with weak immune systems, other co-morbidities, and the elderly can become seriously ill. In 2021, there were 63 confirmed and probable cases reported (1.1 cases per 100,000), a slight increase from the 55 cases in 2019. Over the past decade, slight annual fluctuations in reported cases have been observed, however, reported case numbers continue to trend upward (range, 41 to 72) and are consistently higher than annual cases reported in the previous decade, 2000-2010 (range, 1 to 56) (Figure 1). In recent years, case demographics were similar. In 2021, 37 (59%) of the cases occurred in males. The median case age was 69 years (range, 2 to 92), up slightly from 67 in 2019, and older than the median ages for both anaplasmosis (64 years) and Lyme disease (45 years). Illness onset dates peaked in the summer months: 44 (80%) of the 55 cases with known onset date reported first experiencing symptoms in June, July, or August. Twenty (32%) cases were hospitalized due to their infection in 2021 with a median admission duration of 6 days (range, 2 to 18). Seven patients reported severe complications (e.g., organ failure), and one patient with complications died as a result of their babesiosis infection.

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2020 data is not available.

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Babesiosis is a malaria-like illness caused by a protozoan parasite, typically Babesia microti, which infects red blood cells. B. microti is transmitted to humans by bites from Ixodes scapularis (the blacklegged tick), the same vector that transmits the agents of Lyme disease, human anaplasmosis, one form of human ehrlichiosis, and a strain of Powassan virus. Babesia parasites can also be transmitted by blood transfusion. Although most people infected with Babesia have asymptomatic infections, people with weak immune systems, other co-morbidities, and the elderly can become seriously ill.

In 2019, there were 55 confirmed and probable cases reported (0.97 cases per 100,000), a slight increase from the 49 cases in 2018. Over the past decade, slight annual fluctuations in reported cases have been observed, however, reported case numbers continue to trend upward (range, 41 to 72) and are consistently higher than annual cases reported in the previous decade, 2000-2009 (range, 1 to 31) (Figure 1). In recent years, case demographics were similar. In 2019, 40 (73%) of the cases occurred in males. The median case age was 67 years (range, 4 to 97), up from 64 in 2018, and older than the median ages for both anaplasmosis (62 years) and Lyme disease (48 years). Illness onset dates peaked in the summer months: 40 (77%) of 52 cases with known onset date reported first experiencing symptoms in June, July, or August. Twenty- four (44%) cases were hospitalized due to their infection in 2018 with a median admission duration of 4 days (range, 2 to 10). Seven patients reported severe complications (e.g. organ failure), but there were no deaths attributed to babesiosis infection.

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Babesiosis is a malaria-like illness caused by a protozoan parasite, typically Babesia microti, which infects red blood cells. B. microti is transmitted to humans by bites from I. scapularis (the blacklegged tick), the same vector that transmits the agents of Lyme disease, human anaplasmosis, one form of human ehrlichiosis, and a strain of Powassan virus. Babesia parasites can also be transmitted by blood transfusion. Although most people infected with Babesia have asymptomatic infections, people with weak immune systems, other co-morbidities, and the elderly can become seriously ill.

In 2018, 49 confirmed and probable babesiosis cases (1.1 per 100,000 population) were reported, down slightly from the 59 cases in 2017. Despite slight annual fluctuations, case totals since 2009 (range, 31 to 72) have been consistently higher than reported totals from 2000 to 2008 (range, 1 to 29) (Figure 1), and the overall trend is toward increasing numbers. Demographic and case characteristics are similar in recent years. In 2018, 33 (67%) of the cases occurred in males. The median case age was 64 years (range, 5 to 84), identical to 2017, and older than the median ages for both anaplasmosis (61 years) and for confirmed cases of Lyme disease (44 years). Onsets of illness peaked in the summer months; 36 (86%) of 42 patients with known onset reported first experiencing symptoms in June, July, or August. Fifteen (31%) cases were hospitalized for their infection in 2018 for a median duration of 4 days (range, 2 to 10 days). A single case had severe complications (e.g., organ failure), but there were no deaths attributable to babesiosis.

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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).