Zoonotic and Vector-Borne Infections (Leptospira, Rickettsia, Scrub Typhus, Bartonella) MCQs

Microbiology · 19 free questions with answers & explanations.

1. Scrub typhus is caused by Orientia tsutsugamushi. In India, the 'scrub typhus belt' includes the Himalayan foothills, Northeast India, and parts of South India. The vector-reservoir complex for scrub typhus involves:
2. A rice-field worker in Kerala develops fever, myalgia, conjunctival suffusion, and jaundice with renal failure (Weil's disease) after flooding. MAT (Microscopic Agglutination Test) titre to Leptospira interrogans is 1:800. The first-line antibiotic for severe leptospirosis is:
3. A 22-year-old farmer from Tamil Nadu presents after heavy rain with fever, severe muscle pain, jaundice, conjunctival suffusion, and haematuria. Blood culture on Fletcher's EMJH medium is ordered. Microscopic agglutination test (MAT) with live Leptospira serovars shows titre of 1:800 against serovar Icterohaemorrhagiae. Which complication is this patient at highest risk for, and what antibiotic is used for severe leptospirosis?
4. A 28-year-old immunocompromised HIV patient (CD4 50 cells/µL) develops recurring bacteraemia with gram-negative bacilli forming small vessel angiomatous lesions on skin (bacillary angiomatosis) and liver (peliosis hepatis). Silver stain of skin biopsy shows clumps of extracellular bacilli. What is the most likely causative organism and treatment?
5. A 22-year-old rice-field worker from Kerala presents with biphasic fever, conjunctival suffusion, calf muscle tenderness, and jaundice. Urinalysis shows haematuria and proteinuria. The MAT (microscopic agglutination test) titre is 1:400 for Leptospira icterohaemorrhagiae. The most appropriate treatment for this severe leptospirosis (Weil's disease) is:
6. A rice-field worker from Kerala presents in September with sudden fever, myalgia, conjunctival suffusion, and jaundice. Urinalysis shows proteinuria and casts. Leptospira IgM ELISA is positive. The microscopic agglutination test (MAT) is the reference serological test. What titer is considered significant in the MAT for diagnosis of acute leptospirosis?
7. A 35-year-old farmer from Kerala presents with fever, conjunctival suffusion (hyperaemia without discharge), myalgia particularly in calf muscles, and jaundice with renal failure (Weil's disease). Serology confirms leptospirosis. Which Leptospira serogroup is classically associated with Weil's disease?
8. A construction worker from Kerala develops acute febrile illness with conjunctival suffusion, calf muscle tenderness, thrombocytopaenia, and renal dysfunction after flooding. Leptospira IgM ELISA is positive. Which culture medium and incubation conditions are used to isolate Leptospira from blood in the first week of illness?
9. The Weil-Felix reaction for diagnosis of rickettsial infections uses agglutination of Proteus vulgaris OX strains (OX-2, OX-19, OX-K). A patient with high fever, eschar, and regional lymphadenopathy shows OX-K agglutination (titer 1:160) with negative OX-2 and OX-19. This pattern is diagnostic of:
10. Leptospirosis is best diagnosed by which method in the second week of illness when leptospires have cleared from the blood?
11. Cat scratch disease (CSD) is caused by Bartonella henselae. The histological appearance of lymph node biopsy in CSD shows:
12. A 35-year-old farmer from Kerala presents with 7 days of high fever, conjunctival suffusion, severe myalgia, jaundice, and oliguria. Urine shows proteinuria and casts. Weil-Felix test is negative. IgM ELISA for Leptospira is positive. What confirms the diagnosis of Weil's disease over other diagnoses?
13. A child from a rural forested area in Himachal Pradesh presents with 10 days of fever, an eschar on the neck, and cervical lymphadenopathy. Weil-Felix test shows agglutination of OX-K at 1:320 but not OX-19 or OX-2. Which pathogen is responsible?
14. An HIV-positive patient (CD4 count 80 cells/µL) has been febrile for 3 weeks with splenomegaly and markedly elevated alkaline phosphatase. Blood cultures grow small gram-negative bacilli after 5 days on BACTEC system. Warthin-Starry silver stain of liver biopsy shows bacilli within blood vessel walls. What is the diagnosis?
15. A farmer from Kerala presents with fever, jaundice, conjunctival suffusion, and oliguria after flooding. Leptospirosis is suspected. The GOLD STANDARD diagnostic test is:
16. Scrub typhus is caused by Orientia tsutsugamushi. The diagnostic hallmark on clinical examination is:
17. A 10-year-old child in Rajasthan presents with 3 weeks of undulant fever, hepatosplenomegaly, and arthralgia. The family keeps cattle and the child drinks raw milk. Serology shows a standard tube agglutination test (STAT) for Brucella with a titre of 1:160. The MOST appropriate treatment regimen for brucellosis in this child is:
18. Bartonella henselae, the causative agent of cat scratch disease, is transmitted by:
19. Weil's disease (icteric leptospirosis) is characterised by severe hepatorenal involvement. During which phase does severe organ dysfunction predominantly occur?