STEPTRACKERMICROBIOLOGY + DERMATOLOGY | SPIROCHETES | HIGH-YIELD REVIEW

Spirochetes

Thin, spiral, motile bacteria with axial filaments — too thin for Gram stain, so they're found by dark-field, serology or PCR. Treponema, Borrelia and Leptospira.

FOCUS ON
Syphilis: primary painless chancre → secondary (rash on palms and soles, condylomata lata, lymphadenopathy) → latent → tertiary (gummas, aortitis, tabes dorsalis, Argyll Robertson pupil). Screen with nontreponemal (VDRL/RPR; titers track activity; false ⁺ in SLE, pregnancy, viral infections) and confirm with treponemal (FTA-ABS; stays ⁺). Penicillin G; Jarisch-Herxheimer reaction. Congenital: snuffles, saddle nose, Hutchinson teeth, saber shins. Lyme (B burgdorferi): Ixodes tick, erythema migrans → facial nerve palsy, AV block → arthritis; doxycycline.
STAGE · DISEASE
MECHANISM
CLINICAL PICTURE
CLUE · TREATMENT
Primary syphilis
T pallidum enters at inoculation site (3 weeks)
Painless, indurated, clean-based chancre + painless nodes
Dark-field microscopy of exudate
Secondary syphilis
Hematogenous spread (weeks–months)
Diffuse maculopapular rash incl. palms/soles, condylomata lata (moist, flat), alopecia, lymphadenopathy, fever
Most contagious stage · serology strongly ⁺
Latent syphilis
No symptoms; serology ⁺
Early (< 1 year) or late
Benzathine penicillin weekly × 3 for late latent
Tertiary — cardiovascular
Endarteritis of vasa vasorum
Ascending aortic aneurysm ("tree-bark" intima), aortic regurgitation
Years to decades later
Tertiary — neurosyphilis
Dorsal column and root damage; brain parenchyma
Tabes dorsalis (↓ proprioception, ⁺ Romberg, lightning pains), general paresis, Argyll Robertson pupil (accommodates but doesn't react)
CSF VDRL · IV penicillin G
Tertiary — gummas
Granulomatous necrosis
Destructive lesions of skin, bone, liver
—
Congenital syphilis
Transplacental, any stage (highest risk early maternal)
Early: rhinitis ("snuffles"), rash, hepatosplenomegaly · Late: saddle nose, Hutchinson teeth, mulberry molars, saber shins, CN VIII deafness, interstitial keratitis
Screen every pregnancy · penicillin (desensitize if allergic)
Jarisch-Herxheimer reaction
Killed spirochetes release lipoproteins → cytokines
Fever, chills, myalgia within 24 h of first dose
Also in Lyme, leptospirosis, relapsing fever · supportive
Lyme disease — early
B burgdorferi via Ixodes tick (≥ 24–36 h attached); white-footed mouse reservoir, deer host
Erythema migrans (expanding bull's-eye), flu-like illness
Northeast/upper Midwest US · clinical diagnosis · doxycycline
Lyme — early disseminated
Spread to nerves, heart
Bilateral facial nerve palsy, meningitis, migratory arthralgia, AV block
Ceftriaxone for meningitis or high-grade block
Lyme — late
Persistent infection, immune response
Monoarthritis or oligoarthritis (knee), encephalopathy
Doxycycline (amoxicillin in pregnancy) · ceftriaxone if arthritis persists
Relapsing fever (B recurrentis, others)
Lice or soft ticks; antigenic variation of surface proteins
Recurring fevers separated by afebrile periods
Spirochetes seen on blood smear (Wright/Giemsa)
Leptospirosis
Animal urine in water
Fever, conjunctival suffusion, calf pain → Weil disease (jaundice, AKI)
Doxycycline or penicillin

Mechanism — reading syphilis serology

RPR/VDRLAntibodies to cardiolipin
→
Titer follows activityFalls after treatment
→
False ⁺SLE, antiphospholipid, pregnancy, viral, IVDU
FTA-ABS / TP-PAAntibodies to treponemes
→
Stays ⁺ for life
→
Confirms, can't show cure

Genital ulcers compared

ULCER
PAINFUL?
NODES
ORGANISM
Chancre
No
Painless
T pallidum
Chancroid
Yes
Painful, suppurative
H ducreyi
Herpes
Yes (vesicles)
Tender
HSV-2 / HSV-1
LGV
Painless, transient
Painful buboes
C trachomatis L1–L3
Granuloma inguinale
No, beefy red
None
K granulomatis

How it's tested

COMMON CONFUSIONCondylomata lata (syphilis; flat, moist) vs condylomata acuminata (HPV 6/11; warty, cauliflower).
THE TRAPA positive RPR in a woman with SLE and miscarriages may be a false positive from antiphospholipid antibodies — confirm with a treponemal test.
YOUR APPROACHUlcer or rash → stage → nontreponemal screen → treponemal confirmation → penicillin route and duration → warn about Jarisch-Herxheimer.

If you see… think…

Painless indurated genital ulcer → primary syphilis
Rash on palms and soles + flat moist genital lesions → secondary syphilis
Pupil that accommodates but doesn't react to light → Argyll Robertson (neurosyphilis)
Ascending aortic aneurysm with "tree-bark" intima → syphilitic aortitis
Infant with snuffles, later saddle nose and notched incisors → congenital syphilis
Fever and chills hours after penicillin for syphilis → Jarisch-Herxheimer
Bull's-eye rash after hiking in Connecticut → Lyme (erythema migrans)
Bilateral Bell's palsy or heart block in summer → Lyme disease
Spirochetes on peripheral smear, recurring fevers → relapsing fever (Borrelia)
Calf pain + conjunctival suffusion after freshwater exposure → leptospirosis