Episode 228: Tickborne Illnesses

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

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Tags: Babesiosis, Ehrlichiosis, Infectious Diseases, Lyme Disease, Tick-Borne Illnesses

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Show Notes

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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 staining