Can a tick bite cause neutropenia (low neutrophil count) in a teenager?

Can Tick Bites Cause Neutropenia in Teenagers?

Yes, tick bites can cause neutropenia in teenagers through tickborne rickettsial diseases, particularly human granulocytic anaplasmosis (HGA) and human monocytic ehrlichiosis (HME), which characteristically present with leukopenia including neutropenia along with thrombocytopenia and elevated liver enzymes. 1

Mechanism and Clinical Context

Tickborne rickettsial diseases (TBRD) commonly cause cytopenias, including neutropenia, as part of their clinical presentation:

• Ehrlichiosis (HME and HGA) characteristically causes leukopenia with neutropenia, often accompanied by thrombocytopenia and elevated transaminases 1
• The neutropenia results from increased destruction and consumption of white blood cells during the infection, not from bone marrow failure 1
• In one documented case, an HIV-positive patient with HME presented with a WBC count of 2.0 x 10⁹ cells/L (normal: 4.5-11.0) with 66% neutrophils and 18% bands, demonstrating severe leukopenia with a left shift 1

Key Diagnostic Features

When evaluating a teenager with neutropenia after tick exposure, look for this constellation:

• Fever, headache, myalgias, nausea, and vomiting are the typical presenting symptoms 1
• Thrombocytopenia (platelet count <150 x 10⁹/L) occurs in the majority of cases and is a critical diagnostic clue 1
• Elevated liver enzymes (AST/ALT) are commonly present 1
• Absence of rash is typical in adults with ehrlichiosis, though children may present differently 1
• Up to 40% of patients report no history of tick bite, so absence of reported exposure should not exclude the diagnosis 1

Critical Diagnostic Pitfall

The most dangerous error is attributing neutropenia solely to a tickborne illness without considering alternative diagnoses:

• One case report documented a 51-year-old woman with pancytopenia after a tick bite who was initially thought to have a tickborne illness, but actually had acute myelogenous leukemia with 60% blasts on bone marrow biopsy 2
• If neutropenia is severe (ANC <500/μL) or accompanied by other unexplained cytopenias, peripheral blood smear and potentially bone marrow evaluation are mandatory to exclude primary hematologic disorders 3, 2

Immediate Management Algorithm

When tickborne disease with neutropenia is suspected in a teenager:

1. Initiate doxycycline immediately (2.2 mg/kg orally twice daily) without waiting for serologic confirmation, as delay in treatment can lead to severe disease and fatal outcomes 1
2. Doxycycline is the drug of choice for all ages, including children, as limited courses do not pose substantial risk of tooth staining 1
3. Obtain acute serum for IgG and IgM antibodies to R. rickettsii, E. chaffeensis, and A. phagocytophilum, but do not delay treatment for results 1
4. Order CBC with differential, comprehensive metabolic panel, and blood culture 1
5. If meningococcemia cannot be excluded clinically, add ceftriaxone to cover N. meningitidis while treating for TBRD 1

Important Caveats

Several critical points about neutropenia in tickborne diseases:

• Serologic testing is typically negative in the first week of illness, so negative early serology does not exclude the diagnosis 1
• Morulae (intracytoplasmic inclusions) are seen in only 1-20% of HME cases on peripheral smear, so their absence does not rule out ehrlichiosis 1
• Rocky Mountain Spotted Fever (RMSF) typically presents with normal WBC counts, not neutropenia, though thrombocytopenia is common 1
• Immunocompromised patients (including those with HIV) are at higher risk for severe disease and may present with more profound cytopenias 1

Geographic and Temporal Considerations

TBRD should be considered endemic throughout the contiguous United States, not just in traditionally high-risk areas 1

• Peak tick activity occurs April through September 1
• Approximately 5-15% of lone star ticks carry E. chaffeensis, and 10-50% of I. scapularis ticks carry A. phagocytophilum in endemic areas 1