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Zoonoses & rickettsial infections flashcards

16 high-yield MRCP Part 1 cards from the Intellect Medicos Infectious Diseases course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.

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1. A walker has a typical erythema migrans rash after a tick bite. What investigation is needed before treatment?

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   None — erythema migrans is diagnosed clinically and treated straight away.

   Why? Serology is often negative early. NICE: test only when Lyme disease is suspected without erythema migrans.

2. What is the first-line test when Lyme disease is suspected WITHOUT erythema migrans?

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   ELISA (IgM/IgG) first; if positive (or equivocal), confirm with immunoblot (Western blot).

   Why? Two-tier testing improves specificity.

3. What is the first-line antibiotic for erythema migrans in a non-pregnant adult?

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   Oral doxycycline (21 days, NICE).

   Why? Amoxicillin is the alternative (e.g. in pregnancy).

4. What is the commonest cardiac manifestation of disseminated Lyme disease?

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   Atrioventricular (heart) block.

   Why? Borrelia burgdorferi can infiltrate the conducting system; do an ECG if Lyme carditis is suspected. Bilateral facial palsy is a classic neurological feature.

5. What is the Jarisch–Herxheimer reaction?

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   Fever, rigors and worsening symptoms within hours of starting antibiotics for a spirochaete infection, caused by release of products from dying organisms.

   Why? Seen with syphilis, Lyme disease and leptospirosis. It is self-limiting — treat supportively and do not stop the antibiotic.

6. A wool-factory worker develops a painless black necrotic eschar on his forearm with marked surrounding oedema. What is the first-line antibiotic?

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   Ciprofloxacin (doxycycline is an alternative).

   Why? This is cutaneous anthrax (Bacillus anthracis, a spore-forming Gram-positive rod). Antitoxin is considered in severe or systemic disease.

7. What is the first-line treatment for brucellosis?

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   Doxycycline + rifampicin for 6 weeks (alternative: doxycycline + streptomycin).

   Why? Combination and long duration are needed because Brucella lives inside macrophages and relapses easily.

8. What is the commonest complication of brucellosis?

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   Sacroiliitis (osteoarticular disease).

   Why? Brucellosis follows unpasteurised dairy or animal contact (Middle East, Mediterranean, South Asia) and causes undulant fever. Blood culture is the gold-standard test.

9. A man who went white-water rafting 10 days ago has fever, severe calf pain, conjunctival suffusion, jaundice and acute kidney injury. What is the most likely diagnosis?

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   Weil's disease — severe leptospirosis (Leptospira interrogans).

   Why? Spread by water contaminated with rat urine. Weil's triad: jaundice, AKI and haemorrhage (including pulmonary haemorrhage).

10. What is the gold-standard test for leptospirosis, and which test is used in the first 5 days?

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    Gold standard: microscopic agglutination test (MAT). In the first 5 days: PCR (blood).

    Why? Antibodies appear later, so serology (IgM ELISA, MAT) is used after the first week.

11. How is leptospirosis treated?

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    Mild: oral doxycycline. Moderate–severe: IV benzylpenicillin or IV ceftriaxone.

    Why? Early antibiotics shorten illness; severe disease also needs organ support (e.g. dialysis).

12. Which organism causes culture-negative endocarditis in a farmer, and what is the long-term treatment?

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    Coxiella burnetii (Q fever); doxycycline + hydroxychloroquine for at least 18 months.

    Why? Q fever is caught by inhaling aerosols from sheep, goats or cattle; acute illness is flu-like with atypical pneumonia and hepatitis.

13. What causes cat-scratch disease, and what is used if treatment is needed?

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    Bartonella henselae; azithromycin for complicated or persistent disease.

    Why? Usually a self-limiting papule at the scratch site with tender regional lymphadenopathy.

14. What is the drug of choice for all rickettsial infections (typhus, Rocky Mountain spotted fever)?

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    Doxycycline.

    Why? Start it on clinical suspicion; delay increases mortality, especially in RMSF.

15. Which rickettsial infection is characterised by an eschar at the chigger-mite bite site?

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    Scrub typhus (Orientia tsutsugamushi).

    Why? Found in Asia-Pacific including India. Epidemic typhus is louse-borne; RMSF is tick-borne with a rash that starts at the wrists and ankles, spreads to the trunk and involves the palms and soles.

16. A diabetic rice farmer from Thailand has pneumonia, sepsis and abscesses in his liver, spleen and prostate. What is the likely organism and initial (intensive-phase) treatment?

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    Burkholderia pseudomallei (melioidosis); IV ceftazidime or meropenem for 10–14 days.

    Why? Then oral co-trimoxazole eradication for 3–6 months to prevent relapse. Diabetes is the strongest risk factor.