# Episode 228: Tickborne Illnesses

An episode of [Core EM - Emergency Medicine Podcast](https://invisiblenetwork.ai/podcast/1005774516), 19 Oct 2026.

Audio: https://media.blubrry.com/coreem/content.blubrry.com/coreem/Tickborne_Illnesses_1_.mp3

Tickborne illnesses in the ED: attachment time, the rash, the smear, prophylaxis, & treatment. Hosts: Samantha Nakos, MD Brian Gilberti, MD https://media.blubrry.com/coreem/content.blubrry.com/coreem/Tickborne_Illnesses_1_.mp3 Download Leave a Comment Tags: Babesiosis, Ehrlichiosis, Infectious Diseases, Lyme Disease, Tick-Borne Illnesses Podcast Video Show Notes Core EM Modular CME Course Maximize your commute with the new Core EM Modular CME Course, featuring the most essential content distilled from our top-rated podcast episodes. This course offers 12 audio-based modules packed with pearls! Information and link below. Course Highlights: • Credit: 12.5 AMA PRA Category 1 Credits™ • Curriculum: Comprehensive coverage of Core Emergency Medicine, with 12 modules spanning from Critical Care to Pediatrics. • Cost: • Free for NYU Learners • $250 for Non-NYU Learners Click Here to Register and Begin Module 1 Lyme, Anaplasmosis, Ehrlichiosis & Babesiosis at a Glance Lyme Anaplasmosis Ehrlichiosis Babesiosis Organism B. burgdorferi (spirochete) A. phagocytophilum E. chaffeensis B. microti (protozoan) Vector I. scapularis I. scapularis Lone star tick I. scapularis Attachment time ≥36–48 h Can be <24 h No data Mostly >48 h Key clue EM rash ↓WBC, ↓plt, ↑LFTs ↓WBC, ↓plt, ↑LFTs Hemolysis, ↓plt Smear — Morulae in neutrophils Morulae in monocytes Intra-RBC parasites, Maltese cross Confirm Clinical (EM) Smear, PCR Smear, PCR Smear, PCR Treat Doxy × 10–14 d Doxy × 10 d Doxy until ≥3 d afebrile Atovaquone + azithro × 7–10 d Background • Ixodes scapularis (deer tick) = primary US vector for Lyme, anaplasmosis, and babesiosis; I. pacificus on the West Coast. Ehrlichiosis → lone star tick (Amblyomma americanum), not the deer tick (CDC MMWR 2016) • Why attachment time matters: B. burgdorferi lives in the tick midgut → multiplies and migrates to the salivary glands only after feeding starts → built-in delay • Single infected nymph: 0 of ~90 animals infected at 24 h, ~10% by 48 h, ~70% by 72 h (Eisen 2018) • Anaplasma can transmit w/in 24 h. Babesia ≈ Lyme, not faster: earliest 36 h, mostly after 48 h. True speedster = Powassan virus (w/in 15 min). Attachment time by hx is often unreliable (IDSA Lyme 2020) • Regional variation: US Lyme = B. burgdorferi; Europe = mostly B. afzelii, B. garinii → different clinical picture. Systemic sx w/ EM more common in the US: ~65% vs ~37% in Europe (IDSA Lyme 2020) Lyme: The Rash and the Serology Erythema Migrans • EM in ~70–80% of infections; appears at the bite site 3–30 d post-bite (avg ~7 d) (CDC) • Usually not a bull’s-eye → most early EM is uniformly red • Expanding erythematous patch + endemic area = Lyme until proven otherwise Serology • 2-tier: EIA or IFA → IgM/IgG Western blot (or modified 2-tier: 2 EIAs, no blot) • Early localized dz → often seronegative (as few as ~20% positive w/in 1 wk of noticing EM) → EM in an endemic area = clinical dx, per IDSA (IDSA Lyme 2020) The Other Three: Labs and the Smear Babesiosis • Hunt for hemolytic anemia: ↓Hgb, ↑LDH, ↓haptoglobin, reticulocytosis; ↓plt and ↑LFTs common • Smear: intraerythrocytic parasites. Maltese cross (tetrad) = pathognomonic but infrequent; ring forms more common. PCR more sensitive than smear (IDSA Babesiosis 2020) Anaplasmosis & Ehrlichiosis • Near-identical presentations. Classic triad: leukopenia, thrombocytopenia, transaminitis • Smear: morulae → Anaplasma in neutrophils, Ehrlichia in monocytes. Smear is insensitive → whole-blood PCR confirms (CDC MMWR 2016) Management Post-Bite Prophylaxis (Lyme) • High-risk bite only → all 3: Ixodes tick, highly endemic area, attached ≥36 h (by engorgement or hx); give w/in 72 h of removal (IDSA Lyme 2020) • Doxycycline 200 mg PO × 1 (adults); 4.4 mg/kg PO × 1, max 200 mg (kids) • Landmark RCT: 482 pts w/ I. scapularis bites → EM 0.4% doxy vs 3.2% placebo, efficacy 87% (Nadelman 2001) • Kids <8: doxy traditionally avoided (tooth staining), but a relative CI only → benefit wins. No…

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