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/.
The following two tabs change content below.

Muhammad Durrani

Assistant Clerkship Director & Assistant Research Director at Inspira Medical Center

Like this article?

Share on facebook
Share on Facebook
Share on twitter
Share on Twitter
Share on linkedin
Share on Linkdin
Share on email
Share via Email

Want to support rebelem?

Leave a Comment

Time limit is exhausted. Please reload CAPTCHA.