Treponema pallidum and Borrelia burgdorferi stages

10 ASCP MLS practice questions on Treponema pallidum and Borrelia burgdorferi stages, part of Immunology. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 31-year-old man taking HIV pre-exposure prophylaxis has screening for sexually transmitted infections every 3 months. Nine months ago his treponemal enzyme immunoassay (EIA) was nonreactive, and his visits at 6 and 3 months ago were missed. Today: treponemal EIA reactive; RPR reactive at 1:32; HIV antigen/antibody nonreactive. He has no history of syphilis or its treatment. A full examination of the skin, mouth, genitals and anus finds no ulcer, rash or mucosal lesion and no enlarged lymph nodes, and neurologic and eye examinations are normal. His infection is best staged as:

   1. AEarly latent syphilis
   2. BLate latent syphilis
   3. CSecondary syphilis
   4. DPrimary syphilis

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   Answer: A · Early latent syphilis

   The reactive EIA and RPR confirm untreated syphilis, and a normal examination with no chancre, rash or mucosal lesion makes it latent. By CDC definitions, latent syphilis is early when it was acquired within the past 12 months, and documented seroconversion within that time is one way to show this. His EIA was nonreactive 9 months ago, so he has early latent syphilis, treated with a single dose of benzathine penicillin G. Late latent syphilis, or latent syphilis of unknown duration, is used when the infection cannot be dated to the past year, and it needs three weekly doses. Primary syphilis needs a chancre and secondary syphilis needs skin, mucosal or lymph node signs, none of which he has.

   • B: Late latent applies when infection cannot be dated to the past 12 months, but his test was nonreactive 9 months ago.
   • C: Secondary syphilis has rash, mucosal lesions or lymphadenopathy, which he does not have.
   • D: Primary syphilis needs a chancre, and none was found.

2. Question 2 · Medium

   In the modified two-tiered test (MTTT) for Lyme disease, a positive or equivocal first-tier EIA is followed by:

   1. ABorrelia PCR on a blood sample
   2. BA second EIA using different antigens
   3. CIgM and IgG Western blots
   4. DA repeat of the same EIA in duplicate

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   Answer: B · A second EIA using different antigens

   In the standard two-tiered test, the second tier is an IgM and IgG Western blot. In the modified test, cleared by the FDA in 2019, the second tier is a different EIA, and both EIAs must be positive or equivocal for a positive result. The modified test is more sensitive in early disease and avoids subjective band reading.

   • A: Blood PCR has low sensitivity and is not part of either serologic algorithm.
   • C: Western blots are the second tier of the standard algorithm, not the modified one.
   • D: Repeating the same assay does not add a second, independent tier.

3. Question 3 · Hard

   A patient with secondary syphilis has an RPR titer of 1:128 at diagnosis. Six months after penicillin treatment, it is 1:16 by the same method. How should this be interpreted?

   1. ATreatment failure: the RPR is still reactive
   2. BReinfection: the titer pattern shows a rise
   3. CAdequate response: an eightfold decline
   4. DInadequate: a 16-fold fall is required

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   Answer: C · Adequate response: an eightfold decline

   From 1:128 to 1:16 is three doubling dilutions, an eightfold fall (128 / 16 = 8). An adequate response is at least a fourfold (two-dilution) fall within 6 to 12 months of treating primary or secondary syphilis. The RPR need not become nonreactive; some patients stay low-titer reactive (serofast). Treponemal tests usually stay reactive and are not used to follow treatment.

   • A: A reactive RPR after treatment is common; the size of the fall matters.
   • B: Reinfection would show a fourfold or greater rise.
   • D: A fourfold fall is the accepted criterion.

4. Question 4 · Easy

   When typical erythema migrans appears within days of a tick bite in an endemic area, Lyme serology is:

   1. APositive on the IgM blot in most cases
   2. BRequired to be positive before treatment
   3. CUsually positive for IgG antibodies
   4. DOften negative; the diagnosis is clinical

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   Answer: D · Often negative; the diagnosis is clinical

   Antibodies to Borrelia burgdorferi take a few weeks to rise, so serology is often negative in early localized disease. Typical erythema migrans in an endemic area is diagnosed clinically and treated without testing. Sensitivity rises as the infection disseminates. By late disease, almost all untreated patients have IgG antibodies.

   • A: Most patients with early erythema migrans are still seronegative.
   • B: Treatment should not wait for serology in typical erythema migrans.
   • C: IgG antibodies develop weeks after infection.

5. Question 5 · Medium

   In the diagnosis of neurosyphilis, a reactive CSF-VDRL on a sample free of blood contamination:

   1. AIs highly specific and supports neurosyphilis
   2. BUsually reflects serum antibody in the CSF
   3. CIs sensitive but has low specificity
   4. DMust be confirmed with a CSF RPR

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   Answer: A · Is highly specific and supports neurosyphilis

   The CSF-VDRL is highly specific for neurosyphilis when the sample is not contaminated with blood. It is insensitive, however, so a nonreactive result does not exclude neurosyphilis. The CSF FTA-ABS is more sensitive but less specific, so a nonreactive CSF FTA-ABS makes neurosyphilis unlikely. CSF cell count and protein are also used.

   • B: Serum antibody contaminates CSF mainly through blood in the sample.
   • C: The CSF-VDRL is specific, not sensitive.
   • D: The RPR is not recommended for CSF testing.

6. Question 6 · Hard

   A 30-year-old from Connecticut has had a swollen knee for 2 months, without fever, and no previous Lyme diagnosis or treatment. Lyme EIA positive; IgG Western blot 8 of 10 bands; IgM Western blot negative. The best interpretation is:

   1. AConsistent with Lyme arthritis (late disease)
   2. BNegative, because the IgM blot is negative
   3. CPast infection unrelated to the knee
   4. DEarly localized Lyme disease

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7. Question 7 · Medium

   A man has a painless genital ulcer that appeared 6 days ago. His RPR is nonreactive. What is the best interpretation?

   1. AIt rules out syphilis at this stage
   2. BIt indicates late latent syphilis
   3. CIt does not exclude primary syphilis
   4. DIt shows a prozone reaction

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8. Question 8 · Hard

   A woman has had fatigue and joint aches for 8 months. Lyme first-tier EIA positive; IgM Western blot positive (2 of 3 bands); IgG Western blot negative. The best interpretation is:

   1. ALikely a false-positive IgM result
   2. BLate Lyme disease, confirmed by IgM
   3. CEarly disseminated Lyme disease
   4. DReinfection with B. burgdorferi

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9. Question 9 · Medium

   In untreated syphilis, nontreponemal (RPR) titers are highest, with close to 100% sensitivity, in which stage?

   1. AEarly latent syphilis
   2. BPrimary syphilis
   3. CLate (tertiary) syphilis
   4. DSecondary syphilis

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10. Question 10 · Hard

    A newborn's RPR titer is 1:64 and the treponemal test is reactive. The mother, untreated during pregnancy, has an RPR titer of 1:8 at delivery, by the same method. The best interpretation is:

    1. APassive maternal antibody, no infant infection
    2. BProven or highly probable congenital syphilis
    3. CA biologic false-positive infant RPR
    4. DExpected, since infant titers exceed the mother's

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