At a glance
- Do not wait for confirmatory testing when RMSF, ehrlichiosis, or anaplasmosis is clinically plausible; early doxycycline saves lives.
- Lyme serology can be falsely negative early; erythema migrans is a clinical diagnosis.
- Babesiosis causes hemolytic anemia and thrombocytopenia; diagnose with smear or PCR, not Lyme serology.
- Geography, season, outdoor exposure, cytopenias, transaminitis, rash pattern, and hemolysis are the key bedside clues.
- Doxycycline is appropriate for suspected rickettsial disease in adults and children when disease is suspected.
Objectives
- 1.Distinguish Lyme disease, anaplasmosis, ehrlichiosis, RMSF, and babesiosis by syndrome and lab pattern.
- 2.Know when to treat empirically before diagnostic confirmation.
- 3.Interpret Lyme serology based on timing and pretest probability.
- 4.Choose initial therapy for common tick-borne syndromes.
- 5.Counsel patients about post-treatment symptoms without reflexively extending antibiotics.
Key concepts
Erythema migrans is a clinical diagnosis
Early localized Lyme disease classically presents with erythema migrans, often with fever, fatigue, headache, myalgias, or arthralgias. Serology is frequently negative early because antibodies have not developed. If the lesion is compatible and exposure risk is plausible, treat clinically rather than waiting for testing.
Self-check
A Connecticut resident develops an expanding annular erythematous rash 10 days after hiking. He has fatigue and headache. Lyme ELISA is negative. Best next step?
Select one answer to view the rationale and peer response data.
Two-tier Lyme testing is for compatible syndromes
Lyme serology performs best when the clinical syndrome and epidemiology fit. Testing patients with nonspecific chronic symptoms and low pretest probability increases false positives. Use serology for disseminated manifestations such as facial palsy, carditis, meningitis, or arthritis when compatible.
Self-check
Which patient is the best candidate for Lyme serologic testing?
Select one answer to view the rationale and peer response data.
RMSF is a treat-now diagnosis
Rocky Mountain spotted fever can progress rapidly and early tests are often negative. Fever, severe headache, rash, thrombocytopenia, hyponatremia, and transaminitis should trigger empiric doxycycline when epidemiology fits. Do not withhold doxycycline from children or pregnant patients when RMSF is suspected without expert input.
Self-check
A child has fever, severe headache, thrombocytopenia, hyponatremia, and a petechial rash after camping. RMSF serology is pending. Best management?
Select one answer to view the rationale and peer response data.
Anaplasmosis and ehrlichiosis often look like viral sepsis with cytopenias
Anaplasmosis and ehrlichiosis commonly cause fever, headache, malaise, leukopenia, thrombocytopenia, and mild transaminitis. Rash is more common in ehrlichiosis than anaplasmosis but is not required. PCR is useful early; serology may be negative initially. Treat with doxycycline when suspected.
Self-check
A patient from New England has fever, headache, leukopenia, thrombocytopenia, and AST/ALT elevation in July. No rash. Which treatment is most appropriate while PCR is pending?
Select one answer to view the rationale and peer response data.
Babesiosis is the tick-borne hemolysis syndrome
Babesia microti infection should be suspected with fever, fatigue, hemolytic anemia, thrombocytopenia, elevated bilirubin/LDH, and compatible geography. Asplenia and immunocompromise increase severity. Diagnosis is by blood smear or PCR. Treat symptomatic disease with atovaquone plus azithromycin; severe disease may require clindamycin plus quinine and exchange transfusion consideration.
Self-check
A splenectomized patient has fever after Nantucket travel, hemolytic anemia, thrombocytopenia, and intraerythrocytic parasites on smear. Best usual therapy for non-life-threatening babesiosis?
Select one answer to view the rationale and peer response data.
Coinfection changes the clinical pattern
Ixodes ticks can transmit Lyme, anaplasmosis, and babesiosis. Persistent high fever, cytopenias, transaminitis, or hemolysis should prompt evaluation for coinfection rather than attributing everything to uncomplicated Lyme disease.
Self-check
A patient treated for erythema migrans has persistent high fever, leukopenia, thrombocytopenia, and transaminitis. What is the best next consideration?
Select one answer to view the rationale and peer response data.
Post-treatment Lyme symptoms are not active infection by default
Some patients have fatigue, pain, or cognitive symptoms after appropriate Lyme therapy. Current guidelines do not support prolonged or repeated antibiotics in the absence of objective evidence of active infection. The clinical task is to validate symptoms, reassess for alternate diagnoses, and avoid harm from unnecessary antibiotics.
Self-check
A patient completed guideline-concordant Lyme therapy 4 months ago and has fatigue and diffuse pain but no objective arthritis, meningitis, neuropathy, or carditis. Best approach?
Select one answer to view the rationale and peer response data.
Prophylaxis after tick bite is selective
Single-dose doxycycline prophylaxis is reserved for high-risk Ixodes bites: endemic area, tick attached long enough, prophylaxis started within 72 hours of removal, and no contraindication. Otherwise observe and educate about symptoms.
Self-check
Which exposure best fits single-dose doxycycline prophylaxis for Lyme prevention?
Select one answer to view the rationale and peer response data.
Testing strategy depends on timing
PCR is most useful early for anaplasmosis/ehrlichiosis and smear/PCR for babesiosis. RMSF and ehrlichial serologies often require paired acute and convalescent samples. Lyme serology becomes more sensitive after several weeks. A negative early test should not overrule a dangerous compatible syndrome.
Self-check
Which statement about tick-borne testing is most accurate?
Select one answer to view the rationale and peer response data.
Doxycycline is the empiric anchor for many severe tick-borne syndromes
When fever plus epidemiology plus cytopenias, transaminitis, severe headache, or compatible rash suggests rickettsial disease, doxycycline is the empiric anchor. Amoxicillin may be appropriate for selected Lyme disease, but it does not cover RMSF, anaplasmosis, or ehrlichiosis.
Self-check
Why is amoxicillin a poor empiric choice for undifferentiated febrile tick-borne illness with thrombocytopenia?
Select one answer to view the rationale and peer response data.
Evidence & guidelines
Guidelines
- Diagnosis and management of tickborne rickettsial diseasesBiggs HM, Behravesh CB, Bradley KK, et al. MMWR Recomm Rep. 2016;65(2):1-44. PMID: 27172113. DOI: 10.15585/mmwr.rr6502a1.Essential guidance for RMSF, ehrlichiosis, and anaplasmosis; emphasizes empiric doxycycline without waiting for confirmation.
- 2020 Guidelines for the prevention, diagnosis, and treatment of Lyme diseaseLantos PM, Rumbaugh J, Bockenstedt LK, et al. Clin Infect Dis. 2021;72(1):e1-e48. PMID: 33417672. DOI: 10.1093/cid/ciaa1215.Core Lyme disease reference: erythema migrans, testing strategy, neuroborreliosis, carditis, arthritis, prophylaxis, and post-treatment symptoms.
Pearls
- PearlTreat suspected RMSF now; confirm later.
- PearlEarly negative Lyme serology does not exclude erythema migrans.
- PearlHemolysis after tick exposure should make you think Babesia.
- PearlCytopenias and transaminitis are clues to anaplasmosis/ehrlichiosis.
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