Spirochetes — MCQs
A 34-year-old pregnant woman at 28 weeks gestation is found to have a positive treponemal test (TPHA) but negative non-treponemal test (VDRL) during routine antenatal screening. She has no history of syphilis treatment. What is the most appropriate interpretation and management?
Jarish-Herxheimer reaction is seen in early cases of what?
Which of the following bacteria does not exhibit bipolar staining?
What is the most common form of leptospirosis?
Most specific confirmatory diagnostic test for syphilis:
A sewerage worker presents to OPD with acute febrile illness alongwith jaundice and conjunctivitis. His blood sample was taken and sent to lab . Lab findings are suggestive of kidney failure and elevated hepatic enzymes. Which of following is likely diagnosis ?
Erythema chronicum migrans is associated with which of the following conditions?
HACEK group of organisms includes all, except:
What is the significance of prozone phenomenon in syphilis testing?
What is the most sensitive test for diagnosing syphilis?
Spirochetes Indian Medical PG Practice Questions and MCQs
Question 1: A 34-year-old pregnant woman at 28 weeks gestation is found to have a positive treponemal test (TPHA) but negative non-treponemal test (VDRL) during routine antenatal screening. She has no history of syphilis treatment. What is the most appropriate interpretation and management?
- A. Successfully treated past infection - no treatment needed
- B. Biological false positive - repeat testing in 4 weeks
- C. Latent syphilis cannot be ruled out - treat with benzathine penicillin (Correct Answer)
- D. False positive TPHA - no treatment needed
Explanation: ***Latent syphilis cannot be ruled out - treat with benzathine penicillin*** - A positive **treponemal test (TPHA)** with a **negative non-treponemal test (VDRL)** in a patient with **no documented treatment history** requires treatment in pregnancy to prevent **congenital syphilis**. - This serologic pattern can represent **late latent syphilis** (where VDRL titers may wane over time), **very early primary syphilis** (before VDRL seroconversion), or even previously treated infection with undocumented history. - In pregnancy, when treponemal testing is positive and treatment status is uncertain or undocumented, the standard of care is to **treat presumptively** with **benzathine penicillin G 2.4 million units IM** to protect the fetus from congenital syphilis. - The principle is: **when in doubt, treat** - the risk of untreated maternal syphilis to the fetus far outweighs the minimal risk of unnecessary treatment. *Successfully treated past infection - no treatment needed* - While a positive TPHA with negative VDRL can indicate successfully treated past infection (serofast state), the patient has **no documented history of syphilis treatment**. - Without documentation of adequate treatment, one cannot assume prior successful treatment - this would put the fetus at unacceptable risk for **congenital syphilis** (which can cause stillbirth, neonatal death, and severe congenital abnormalities). - CDC and WHO guidelines recommend treatment in pregnancy when treatment history is uncertain or undocumented. *Biological false positive - repeat testing in 4 weeks* - **Biological false positives** typically occur with **non-treponemal tests** (VDRL/RPR) in conditions like pregnancy, autoimmune diseases, or acute infections, usually presenting as positive VDRL/RPR with negative confirmatory treponemal testing. - A positive **TPHA (treponemal test)** is highly specific for treponemal infection and rarely gives false positives. - Delaying treatment for repeat testing in 4 weeks is inappropriate in pregnancy when treponemal testing is positive - this creates unnecessary risk for vertical transmission and congenital syphilis. *False positive TPHA - no treatment needed* - **TPHA** (Treponema pallidum Hemagglutination Assay) is a highly specific treponemal test with very low false-positive rates. - False-positive treponemal tests are rare and typically occur in conditions like Lyme disease or other spirochetal infections. - Given the high specificity of TPHA and the critical importance of preventing congenital syphilis, dismissing a positive result as false positive without treatment is clinically inappropriate and potentially harmful.
Question 2: Jarish-Herxheimer reaction is seen in early cases of what?
- A. Syphilis (Correct Answer)
- B. Gonorrhea
- C. Lymphogranuloma venereum
- D. Granuloma inguinale
Explanation: ***Syphilis*** - The **Jarisch-Herxheimer reaction** is an acute, self-limiting febrile reaction that occurs within a few hours of treatment initiation for spirochetal infections, most notably **syphilis** [1]. - It results from the release of **endotoxins** from dying spirochetes, leading to systemic inflammatory symptoms such as fever, chills, myalgia, headache, and exacerbation of existing skin lesions [1]. *Gonorrhea* - **Gonorrhea** is caused by the bacterium *Neisseria gonorrhoeae*, which is not a spirochete and does not typically trigger a Jarisch-Herxheimer reaction upon treatment. - Treatment for gonorrhea, usually with antibiotics like ceftriaxone, does not result in the rapid release of toxins associated with this specific immunologic response. *Lymphogranuloma venereum* - **Lymphogranuloma venereum (LGV)** is caused by specific serovars of *Chlamydia trachomatis* and is characterized by genital ulcers and prominent lymphadenopathy. - As it is not a spirochetal infection, treatment with antibiotics like doxycycline does not induce a Jarisch-Herxheimer reaction. *Granuloma inguinale* - **Granuloma inguinale**, also known as donovanosis, is caused by *Klebsiella granulomatis*. - This bacterial infection, characterized by progressive ulcerative lesions, is not a spirochetal disease, and thus, treatment does not lead to a Jarisch-Herxheimer reaction.
Question 3: Which of the following bacteria does not exhibit bipolar staining?
- A. Haemophilus influenzae (Correct Answer)
- B. Yersinia pestis
- C. Calymmatobacterium granulomatis
- D. Francisella tularensis
Explanation: ***Haemophilus influenzae*** - *Haemophilus influenzae* is a **pleomorphic coccobacillus** that typically stains uniformly and does not exhibit characteristic **bipolar staining**. - Its presence is often identified by Gram stain showing small, Gram-negative rods, but without the distinctive safety pin appearance. *Calymmatobacterium granulomatis* - *Calymmatobacterium granulomatis* (now *Klebsiella granulomatis*) is known to exhibit **bipolar staining**, often described as a **"safety pin" appearance**, especially in tissue smears from granuloma inguinale lesions. - This characteristic staining is due to the concentration of stain at the ends of the rod-shaped bacteria. *Yersinia pestis* - *Yersinia pestis*, the causative agent of plague, is classically described as having **bipolar staining**, giving it a distinctive **"safety pin" appearance** under a microscope. - This finding is a key diagnostic feature, particularly when observed in Gram-stained smears of clinical samples. *Francisella tularensis* - *Francisella tularensis* is a small, Gram-negative coccobacillus that is known to exhibit **bipolar staining**, though it may be less prominent than in *Yersinia pestis*. - This characteristic can assist in the microscopic identification of the bacterium, which causes tularemia.
Question 4: What is the most common form of leptospirosis?
- A. Icteric form
- B. Hepatorenal form
- C. Anicteric form (Correct Answer)
- D. Weil's disease
Explanation: ***Anicteric form*** - The **anicteric form** accounts for about 90% of all leptospirosis cases, presenting with milder, flu-like symptoms without jaundice. - Patients typically experience **fever, headache, myalgia**, and conjunctival suffusion during the initial septicemic phase [1], followed by an immune phase that can involve meningitis or uveitis [1]. *Icteric form* - The **icteric form** (Weil's disease) is a severe manifestation, characterized by jaundice, renal failure, and hemorrhage, occurring in a minority of cases (5-10%). - Although more severe and often life-threatening, it is **less common** than the anicteric presentation [1]. *Hepatorenal form* - This term describes the severe complications of leptospirosis, including **liver and kidney dysfunction**, specifically associated with Weil's disease. - While a critical aspect of severe leptospirosis, it is a description of the organ involvement rather than a distinct common form of the disease. *Weil's disease* - **Weil's disease** is the most severe and potentially fatal form of leptospirosis, characterized by **jaundice, renal failure, hemorrhage, and myocarditis**. - It is a severe subset of the icteric form, making it a very serious but **uncommon variant** of the overall disease.
Question 5: Most specific confirmatory diagnostic test for syphilis:
- A. IgG ELISA
- B. RPR
- C. FTA-ABS (Correct Answer)
- D. VDRL
Explanation: ***FTA-ABS*** - The **fluorescent treponemal antibody absorption (FTA-ABS)** test specifically detects antibodies against *Treponema pallidum*, making it highly **specific and confirmatory** for syphilis. - It remains positive for life, even after successful treatment, indicating past or present infection. *IgG ELISA* - While IgG ELISA can detect *Treponema pallidum* antibodies, it is generally considered a **screening test** rather than the most specific confirmatory test. - It can yield false positives in some autoimmune conditions, making it less specific than FTA-ABS for confirmation. *RPR* - The **Rapid Plasma Reagin (RPR)** test is a **nontreponemal screening test** for syphilis that detects antibodies indirectly. - It can be positive in other conditions (e.g., autoimmune diseases, pregnancy, or other infections) and is therefore **not specific** for syphilis. *VDRL* - The **Venereal Disease Research Laboratory (VDRL)** test is another **nontreponemal screening test** that detects antibodies to cardiolipin, a lipid-like antigen. - Like RPR, it is prone to **false positives** in various conditions and is used for screening and monitoring treatment response, not definitive confirmation.
Question 6: A sewerage worker presents to OPD with acute febrile illness alongwith jaundice and conjunctivitis. His blood sample was taken and sent to lab . Lab findings are suggestive of kidney failure and elevated hepatic enzymes. Which of following is likely diagnosis ?
- A. Leptospirosis (Correct Answer)
- B. Typhoid
- C. Malaria
- D. Hepatitis A
Explanation: ***Leptospirosis*** - The patient's occupation as a **sewerage worker** points to potential exposure to contaminated water, a known risk factor for leptospirosis [1]. - The classic triad of **febrile illness**, **jaundice**, and **conjunctivitis**, combined with **kidney failure** and **elevated hepatic enzymes**, is highly characteristic of severe leptospirosis (Weil's disease) [1], [2]. *Typhoid* - While typhoid can cause fever and, in severe cases, liver dysfunction, it is typically associated with **gastrointestinal symptoms** like abdominal pain and constipation/diarrhea [2]. - **Conjunctivitis** and significant **jaundice** with acute kidney failure are not typical presenting features of typhoid [2]. *Malaria* - Malaria presents with **cyclical fevers**, **chills**, and **sweats**, and can cause jaundice and kidney injury in severe cases [2]. - However, **conjunctivitis** as a prominent symptom is less common, and the distinct occupational exposure makes leptospirosis more likely [1], [2]. *Hepatitis A* - Hepatitis A causes **jaundice** and **elevated hepatic enzymes**, but it is primarily a liver infection and does not typically lead to acute **kidney failure** [3]. - While fever can be present, **conjunctivitis** and rapid progression to kidney failure are not characteristic of Hepatitis A [3].
Question 7: Erythema chronicum migrans is associated with which of the following conditions?
- A. Lyme disease (Correct Answer)
- B. Glucagonoma
- C. Gastrinoma
- D. Phaeochromocytoma
Explanation: ***Lyme disease*** - **Erythema chronicum migrans** (ECM) is the characteristic expanding annular rash seen in the early localized stage of **Lyme disease**. - It results from infection with **Borrelia burgdorferi**, transmitted by **Ixodes ticks**. *Glucagonoma* - This is a pancreatic neuroendocrine tumor that secretes **glucagon**. - It is classically associated with **necrolytic migratory erythema**, a distinct rash, not erythema chronicum migrans. *Gastrinoma* - A gastrinoma is a tumor that secretes **gastrin**, leading to **Zollinger-Ellison syndrome**, characterized by severe peptic ulcer disease. - It is not associated with skin rashes like erythema chronicum migrans. *Phaeochromocytoma* - This is a tumor of the adrenal medulla that secretes **catecholamines**, causing symptoms like hypertension, palpitations, and headaches. - It does not present with erythema chronicum migrans or other characteristic skin rashes.
Question 8: HACEK group of organisms includes all, except:
- A. Cardiobacterium hominis
- B. Eikenella corrodens
- C. Haemophilus parainfluenzae
- D. Haemophilus ducreyi (Correct Answer)
Explanation: ***Haemophilus ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection, and is not considered part of the HACEK group. - The **HACEK group** consists of fastidious, gram-negative bacteria known for causing **endocarditis**. *Haemophilus parainfluenzae* - *Haemophilus parainfluenzae* is one of the five genera included in the **HACEK group** acronym, specifically the 'H'. - This organism is a known cause of **infective endocarditis**, particularly in patients with pre-existing valvular disease. *Cardiobacterium hominis* - *Cardiobacterium hominis* is represented by the 'C' in the **HACEK group** acronym. - It is a significant cause of **culture-negative endocarditis** due to its fastidious nature and slow growth. *Eikenella corrodens* - *Eikenella corrodens* is the 'E' in the **HACEK group** acronym. - It is often associated with **oral cavity infections**, human bite wounds, and can cause **endocarditis** in susceptible individuals.
Question 9: What is the significance of prozone phenomenon in syphilis testing?
- A. False negative result in early primary syphilis
- B. False positive result in treated syphilis
- C. False negative result in high-titer secondary syphilis (Correct Answer)
- D. False positive result in pregnancy
Explanation: ***False negative result in high-titer secondary syphilis*** - The **prozone phenomenon** occurs when extremely high concentrations of antibodies saturate all available antigen-binding sites, preventing effective lattice formation required for agglutination. - This leads to a **false negative result** because the reaction appears negative despite the presence of a target antigen in the sample, commonly observed in **secondary syphilis** due to high antibody titers. *False negative result in early primary syphilis* - In **early primary syphilis**, antibody titers are still low, not high enough to induce the prozone phenomenon. - **False negatives** in early primary syphilis are typically due to insufficient time for antibody production, rather than antibody excess. *False positive result in treated syphilis* - **Treated syphilis** generally results in declining antibody titers, which would not cause a false positive due to prozone. - A **false positive** result means the test is positive when the condition is not present or has been treated, which is not usually caused by prozone. *False positive result in pregnancy* - Pregnancy can sometimes cause **biological false positives** in non-treponemal tests due to autoimmune reactions or other factors. - However, this is not related to the **prozone phenomenon**, which is caused by antibody excess.
Question 10: What is the most sensitive test for diagnosing syphilis?
- A. VDRL
- B. RPR
- C. TP-PA
- D. FTA-ABS (Correct Answer)
Explanation: ***FTA-ABS*** - The **fluorescent treponemal antibody absorption (FTA-ABS)** test is a treponemal test that is highly sensitive (>95%) and specific for detecting antibodies to *Treponema pallidum*. - It was traditionally considered the gold standard confirmatory test and is often used to confirm positive screening results. - It detects antibodies early in infection and remains positive for life, even after successful treatment. - **Note:** Modern treponemal tests like TP-PA have comparable sensitivity, but FTA-ABS remains widely recognized in clinical practice. *VDRL* - The **Venereal Disease Research Laboratory (VDRL)** test is a non-treponemal test that measures antibodies to cardiolipin, a lipid released from damaged host cells and *T. pallidum*. - While useful for screening and monitoring treatment response (titers decrease with successful treatment), it is less sensitive than treponemal tests, especially in early primary and late/tertiary syphilis. - Can yield false positives in various conditions (pregnancy, autoimmune diseases, infections). *TP-PA* - The **Treponema pallidum particle agglutination (TP-PA)** test is a highly sensitive and specific treponemal test that detects antibodies to *T. pallidum*. - It has sensitivity comparable to FTA-ABS (>95%) and is increasingly preferred in modern laboratories due to easier performance and objective reading. - Like other treponemal tests, it remains positive for life. *RPR* - The **rapid plasma reagin (RPR)** test is a non-treponemal test similar to VDRL, detecting antibodies to cardiolipin. - It is commonly used for screening due to ease of use and ability to monitor treatment response through quantitative titers. - Like VDRL, it has lower sensitivity compared to treponemal tests and can produce false positives.
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