Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 2 Anaplasmosis




  • Overall annual incidence rose from 1.4 to 6.1 cases per million in the United States between 2000 and 2010 (Ismail 2017)
  • In endemic areas, the incidence rate is suggested to be more than 50 cases per 100,000 (Ismail 2017)


  • Median age is 51 years of age with greater than 95% of cases reported in Caucasian patients (Ismail 2017)


  • Slight male to female predominance (Demma 2006)

Morbidity/Mortality: Case fatality rate is less than 1% (Ismail 2017)

  • Many patients will be either asymptomatic or manifest mild signs and symptoms
  • Hospitalization rates have been noted to be as high as 36% in epidemiological studies with a 7% ICU admission rate and mortality rate of 0.6% in those with severe symptoms (Dumler 2012)

Geography and Seasonality (Baker 2020): Upper Midwestern and Northeastern United States

  • Ten States account for over 90% of all reported cases (in order from highest concentration of cases): Minnesota, Wisconsin, Massachusetts, New York, Maine, Connecticut, New Jersey, Rhode Island, Vermont, and New Hampshire.
  • Seasonal distribution is concentrated in summer months corresponding to nymphal tick activity: June (23.4%), July (22.2%), August (12%), and May (10.4%).
    • Second smaller peak is noted in October and November when adult ticks are active

Poor Prognostic Factors:

  • Increased Age
  • Immunocompromised States
  • Delays in diagnosis and treatment

Pathogenesis (Biggs 2016):

  • After tick transmissibility, Anaplasma phagocytophilum has a predilection for granulocytes, specifically neutrophils
  • Once infected, the organism multiplies within cytoplasmic membrane-bound vacuoles forming clusters of bacterial called morulae
  • Infection elicits a systemic inflammatory response and alters the host’s neutrophil function leading to ineffective inflammatory regulation and microbicidal activity

History and Physical:

Symptoms (Ismail 2017, Biggs 2016):

  • Symptoms typically appear 5-14 days after bite of an infected tick
  • Rash is present in less than 10% of patients
  • Fever occurs in 92-100% of recognized cases of anaplasmosis along with other non-specific flu-like symptoms:
    • Headache
    • Malaise
    • Myalgias
    • Chills/Rigors
    • Arthralgias
  • Gastrointestinal symptoms are less frequently seen
  • Central Nervous System involvement is rare
  • Severe Manifestations: Most cases are self-limiting, but Anaplasmosis has been associated with the following severe disease manifestations:
    • ARDS
    • DIC
    • Rhabdomyolysis
    • Renal Failure
    • Pancreatitis
    • Hemophagocytic Syndromes
    • Opportunistic Viral and Fungal infection


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

  • Leukopenia
  • Mild Anemia
  • Thrombocytopenia
  • Mild to Moderate Elevated Hepatic Transaminase
  • Increased Number of Immature Neutrophils

Blood Smear:

  • May see morulae within granulocytes with microscopic examination of blood smears but blood smear may be relatively insensitive and inconsistent and dependent on operator experience (Biggs 2016)
  • Observation of morulae is highly suggestive of infection

Confirmatory Testing (Ismail 2017):

  • Serological testing of IgM and IgG antibodies specific to A phagocytophilum using indirect immunofluorescence assay (IFA) is the gold standard.
  • RT-PCR assays are also available for diagnosis of A phagocytophilum and has become the test of choice due to rapid turnaround times and high specificity as well as sensitivity

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. Todd S et al. No visible dental staining in children treated with doxycycline for suspected Rocky Mountain Spotted Fever. J Pediatr. 2015. PMID: 25794784
  3. Volovitz B et al. Absence of tooth staining with doxycycline treatment in young children. Clin Pediatr (Phila). 2007. PMID: 17325084
  4. Ismail N et al. Tick-Borne Emerging Infections: Ehrlichiosis and Anaplasmosis. Clin Lab Med. 2017. PMID: 28457353
  5. Demma L et al. Human monocytic ehrlichiosis and human granulocytic anaplasmosis in the United States, 2001–2002. Ann N Y Acad Sci. 2006. PMID: 17114690

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 2 Anaplasmosis", REBEL EM blog, November 3, 2020. Available at: https://rebelem.com/emerging-tick-borne-illnesses-not-just-lyme-disease-part-2-anaplasmosis/.

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