Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 5 Babesiosis




  • Overall annual incidence rose from 0.6 to 0.9 cases per 100,000 in the United States between 2012 and 2015 (Gray 2019)
  • Annual incidence is highest in those between 60-69 years of age (Gray 2019)


  • Median age is 63 years of age with greater than 89% of cases reported in Caucasian patients (Gray 2019 2010)


  • Male to female predominance (Gray 2019)


  • Overall hospitalization rates for confirmed cases are noted to range from 16% to 72.6% depending on the patient’s age (Gray 2019)
  • Mortality rates up to 10% have been noted in hospitalized patients (Vannier 2015)
    • Mortality rates are much higher among immunocompromised patients and those who acquired the illness through blood transfusion

Geography and Seasonality (Gray 2019): Cases predominately in the Northeastern and Upper Midwestern United States

  • Seven States account for over 94% of all reported cases:
    • New York
    • Massachusetts
    • Connecticut
    • New Jersey
    • Rhode Island
    • Wisconsin
    • Minnesota
  • Seasonal distribution is concentrated in June, July, and August

Poor Prognostic Factors (Vannier 2015):

  • Neonates and > 50 years of age
  • Coinfection with Lyme Disease
  • Immunocompromised states
  • Delays in diagnosis and treatment
  • Asplenia

Pathogenesis (Krause 2019):

  • After tick transmissibility, Babesia species, an intraerythrocytic protozoa, will mature, replicate, and release into the bloodstream to invade nearby red blood cells
  • This infection leads to erythrocyte lysis, metabolic alterations, proinflammatory cytokine production, and obstruction of blood vessels

History and Physical:

Symptoms (Vannier 2015):

  • Symptoms typically appear 1-4 weeks after bite of an infected tick
  • Rash is not a common occurrence unlike other tick-borne illnesses
    • If present, it should raise the suspicion for co-infection with Lyme disease
  • Fever occurs in 89% of recognized cases of babesiosis along with other non-specific flu-like symptoms:
    • Fatigue
    • Chills
    • Headache
    • Anorexia
    • Myalgia
    • Emotional liability and depression
  • Gastrointestinal symptoms are often seen
  • Physical Examination:
    • Mild splenomegaly and hepatomegaly are sometimes found on examination
    • Jaundice and dark urine are sometimes found on examination due to intravascular hemolysis
  • Severe Manifestations: Most cases are self-limiting, but Babesiosis has been associated with the following severe disease manifestations:
    • ARDS
    • Renal Failure and Hepatic Failure
    • Rhabdomyolysis
    • DIC
    • Heart Failure
    • Coma
    • Splenic Rupture
    • Hemophagocytic Syndromes


Labs: Characteristic laboratory findings are seen in Babesiosis along fever and non-specific flu-like illness:

  • Thrombocytopenia
  • Hemolytic Anemia
  • Low Haptoglobin Level
  • Elevated Reticulocyte Count
  • Elevated LDH Level
  • Elevated Indirect Bilirubin and Mildly Elevated Hepatic Transaminase

Blood Smear (Vannier 2015):

  • Diagnosis can be made with visualization of Babesia parasites on Giemsa or Wright stained thin blood smears.
  • The level of parasitemia is typically between 1 and 10% but can be as high as 80% in severe disease.
  • Babesia species sometimes exhibit the presence of tetrads (Maltese cross) and have the absence of hemozin deposit in the ring form as well as lack banana-shaped shaped gametocytes, thus distinguishing them from plasmodia species.

Confirmatory Testing:

  • Serological testing of IgM and IgG antibodies specific to Babesia species using indirect immunofluorescence assay (IFA) is available for confirmation.
  • RT-PCR assays are also available for diagnosis of Babesiosis with have high sensitivity and specificity.

Guest Post By:

Akash Ray, DO
PGY-2 Emergency Medicine Resident Inspira Medical Center
Vineland, NJ
Twitter: @_kashray


  1. Biggs H et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis – United States. MMWR Recomm Rep. 2016. PMID: 27172113
  2. Gray E et al. Babesiosis Surveillance – United States, 2011-2015. MMWR Surveill Summ. 2019. PMID: 31145719
  3. Vannier E et al. Babesiosis. Infect Dis Clin North Am. 2015. PMID: 25999229
  4. Krause P. Human babesiosis. Int J Parasitol. 2019. PMID: 30690090

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

Cite this article as: Muhammad Durrani, "Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 5 Babesiosis", REBEL EM blog, November 6, 2020. Available at: https://rebelem.com/emerging-tick-borne-illnesses-not-just-lyme-disease-part-5-babesiosis/.

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