MCB 1000L Case Study 5: Shingles & Yellow
Fever Case Scenarios | Questions and
Answers | Microbiology Laboratory |
2026/2027 Updated | 100% Correct
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
48 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
This laboratory case-study exam integrates clinical microbiology, virology, immunology, and epidemiology
through the lens of two classic infectious disease scenarios: herpes zoster (shingles) and yellow fever.
Students must apply diagnostic reasoning, interpret laboratory data, and demonstrate understanding of viral
pathogenesis, transmission, prevention, and public health management.
STUDY GUIDE
Recommended duration: 2 hours. Passing target: 70%.
HIGHP - Page 1 of 17
,1. A patient presents with a painful, unilateral vesicular rash in a dermatomal distribution.
Which laboratory finding would best confirm reactivation of latent varicella-zoster virus?
[ ] A. Positive Tzanck smear showing multinucleated giant cells
[ ] B. Detection of VZV DNA by PCR from vesicle fluid
[ ] C. Elevated IgM antibody titers against VZV in serum
[ ] D. Positive viral culture on human diploid fibroblasts within 24 hours
CORRECT: B. Detection of VZV DNA by PCR from vesicle fluid
PCR detection of VZV DNA from vesicle fluid is the most sensitive and specific method for confirming active
VZV reactivation. Tzanck smear is nonspecific and cannot distinguish VZV from HSV. IgM may be falsely
negative or delayed, and viral culture is slow and less sensitive than PCR.
2. A traveler returning from a tropical region presents with fever, jaundice, and
hemorrhagic signs. Which laboratory test is most appropriate for early confirmation of
yellow fever virus infection?
[ ] A. Serum IgM antibody capture ELISA
[ ] B. Reverse transcriptase PCR (RT-PCR) for YFV RNA
[ ] C. Liver biopsy with immunohistochemistry
[ ] D. Plaque reduction neutralization test (PRNT)
CORRECT: B. Reverse transcriptase PCR (RT-PCR) for YFV RNA
RT-PCR detects YFV RNA in serum during the acute phase (first 3-4 days) and is the preferred early
diagnostic method. IgM ELISA may be negative early and cross-reacts with other flaviviruses. Liver biopsy is
invasive and not routine, and PRNT is used for confirmation later in disease.
3. Which of the following best explains why yellow fever virus is classified as a zoonotic
arbovirus?
[ ] A. It is transmitted by Aedes aegypti mosquitoes and maintained in non-human primate reservoirs.
[ ] B. It is transmitted via respiratory droplets from infected humans.
[ ] C. It is maintained in rodent populations and transmitted by ticks.
[ ] D. It is transmitted by sandflies and maintained in canine reservoirs.
CORRECT: A. It is transmitted by Aedes aegypti mosquitoes and maintained in non-human primate
reservoirs.
Yellow fever virus is an arbovirus transmitted primarily by Aedes aegypti mosquitoes, with non-human
primates serving as the natural reservoir in sylvatic cycles. Respiratory, tick-borne, and sandfly transmission
are not characteristic of YFV.
HIGHP - Page 2 of 17
, 4. A patient with shingles is prescribed acyclovir. Which mechanism best explains its
antiviral activity against VZV?
[ ] A. Inhibition of viral DNA polymerase after phosphorylation by viral thymidine kinase
[ ] B. Blockade of viral entry by binding to the gB glycoprotein
[ ] C. Inhibition of viral protease required for capsid assembly
[ ] D. Prevention of viral mRNA cap formation by targeting the viral guanylyltransferase
CORRECT: A. Inhibition of viral DNA polymerase after phosphorylation by viral thymidine kinase
Acyclovir is a nucleoside analog that requires phosphorylation by viral thymidine kinase and then cellular
kinases; the active triphosphate inhibits viral DNA polymerase. It does not block entry, protease, or mRNA
capping.
5. Which of the following is the most appropriate specimen for laboratory diagnosis of
suspected yellow fever in a patient who is 10 days post-onset of symptoms?
[ ] A. Whole blood for viral culture
[ ] B. Serum for IgM antibody detection
[ ] C. Cerebrospinal fluid for RT-PCR
[ ] D. Urine for viral isolation
CORRECT: B. Serum for IgM antibody detection
At 10 days post-onset, the viremic phase has typically passed, so RT-PCR and culture are less likely to be
positive. IgM antibodies against YFV become detectable around day 5-7 and are the preferred diagnostic
marker at this stage. CSF and urine are not standard specimens for YFV diagnosis.
6. A laboratory technician is processing a blood sample from a patient suspected of
having yellow fever. Which biosafety level and precaution are most appropriate?
[ ] A. BSL-2 with standard precautions
[ ] B. BSL-3 with HEPA-filtered respiratory protection
[ ] C. BSL-4 with positive-pressure suit
[ ] D. BSL-2 with additional airborne precautions
CORRECT: A. BSL-2 with standard precautions
Yellow fever virus is a Risk Group 3 agent, but routine diagnostic work with serum can be performed in BSL-2
with standard precautions, as it is not transmitted by aerosol in the laboratory. BSL-3 is required for culture
and animal studies. BSL-4 is not required, and airborne precautions are not indicated.
7. Which of the following statements correctly describes the difference between varicella
and herpes zoster?
[ ] A. Varicella is caused by VZV, while herpes zoster is caused by HSV-1.
[ ] B. Varicella is the primary infection, while herpes zoster is reactivation of latent VZV.
HIGHP - Page 3 of 17
Fever Case Scenarios | Questions and
Answers | Microbiology Laboratory |
2026/2027 Updated | 100% Correct
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
48 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
This laboratory case-study exam integrates clinical microbiology, virology, immunology, and epidemiology
through the lens of two classic infectious disease scenarios: herpes zoster (shingles) and yellow fever.
Students must apply diagnostic reasoning, interpret laboratory data, and demonstrate understanding of viral
pathogenesis, transmission, prevention, and public health management.
STUDY GUIDE
Recommended duration: 2 hours. Passing target: 70%.
HIGHP - Page 1 of 17
,1. A patient presents with a painful, unilateral vesicular rash in a dermatomal distribution.
Which laboratory finding would best confirm reactivation of latent varicella-zoster virus?
[ ] A. Positive Tzanck smear showing multinucleated giant cells
[ ] B. Detection of VZV DNA by PCR from vesicle fluid
[ ] C. Elevated IgM antibody titers against VZV in serum
[ ] D. Positive viral culture on human diploid fibroblasts within 24 hours
CORRECT: B. Detection of VZV DNA by PCR from vesicle fluid
PCR detection of VZV DNA from vesicle fluid is the most sensitive and specific method for confirming active
VZV reactivation. Tzanck smear is nonspecific and cannot distinguish VZV from HSV. IgM may be falsely
negative or delayed, and viral culture is slow and less sensitive than PCR.
2. A traveler returning from a tropical region presents with fever, jaundice, and
hemorrhagic signs. Which laboratory test is most appropriate for early confirmation of
yellow fever virus infection?
[ ] A. Serum IgM antibody capture ELISA
[ ] B. Reverse transcriptase PCR (RT-PCR) for YFV RNA
[ ] C. Liver biopsy with immunohistochemistry
[ ] D. Plaque reduction neutralization test (PRNT)
CORRECT: B. Reverse transcriptase PCR (RT-PCR) for YFV RNA
RT-PCR detects YFV RNA in serum during the acute phase (first 3-4 days) and is the preferred early
diagnostic method. IgM ELISA may be negative early and cross-reacts with other flaviviruses. Liver biopsy is
invasive and not routine, and PRNT is used for confirmation later in disease.
3. Which of the following best explains why yellow fever virus is classified as a zoonotic
arbovirus?
[ ] A. It is transmitted by Aedes aegypti mosquitoes and maintained in non-human primate reservoirs.
[ ] B. It is transmitted via respiratory droplets from infected humans.
[ ] C. It is maintained in rodent populations and transmitted by ticks.
[ ] D. It is transmitted by sandflies and maintained in canine reservoirs.
CORRECT: A. It is transmitted by Aedes aegypti mosquitoes and maintained in non-human primate
reservoirs.
Yellow fever virus is an arbovirus transmitted primarily by Aedes aegypti mosquitoes, with non-human
primates serving as the natural reservoir in sylvatic cycles. Respiratory, tick-borne, and sandfly transmission
are not characteristic of YFV.
HIGHP - Page 2 of 17
, 4. A patient with shingles is prescribed acyclovir. Which mechanism best explains its
antiviral activity against VZV?
[ ] A. Inhibition of viral DNA polymerase after phosphorylation by viral thymidine kinase
[ ] B. Blockade of viral entry by binding to the gB glycoprotein
[ ] C. Inhibition of viral protease required for capsid assembly
[ ] D. Prevention of viral mRNA cap formation by targeting the viral guanylyltransferase
CORRECT: A. Inhibition of viral DNA polymerase after phosphorylation by viral thymidine kinase
Acyclovir is a nucleoside analog that requires phosphorylation by viral thymidine kinase and then cellular
kinases; the active triphosphate inhibits viral DNA polymerase. It does not block entry, protease, or mRNA
capping.
5. Which of the following is the most appropriate specimen for laboratory diagnosis of
suspected yellow fever in a patient who is 10 days post-onset of symptoms?
[ ] A. Whole blood for viral culture
[ ] B. Serum for IgM antibody detection
[ ] C. Cerebrospinal fluid for RT-PCR
[ ] D. Urine for viral isolation
CORRECT: B. Serum for IgM antibody detection
At 10 days post-onset, the viremic phase has typically passed, so RT-PCR and culture are less likely to be
positive. IgM antibodies against YFV become detectable around day 5-7 and are the preferred diagnostic
marker at this stage. CSF and urine are not standard specimens for YFV diagnosis.
6. A laboratory technician is processing a blood sample from a patient suspected of
having yellow fever. Which biosafety level and precaution are most appropriate?
[ ] A. BSL-2 with standard precautions
[ ] B. BSL-3 with HEPA-filtered respiratory protection
[ ] C. BSL-4 with positive-pressure suit
[ ] D. BSL-2 with additional airborne precautions
CORRECT: A. BSL-2 with standard precautions
Yellow fever virus is a Risk Group 3 agent, but routine diagnostic work with serum can be performed in BSL-2
with standard precautions, as it is not transmitted by aerosol in the laboratory. BSL-3 is required for culture
and animal studies. BSL-4 is not required, and airborne precautions are not indicated.
7. Which of the following statements correctly describes the difference between varicella
and herpes zoster?
[ ] A. Varicella is caused by VZV, while herpes zoster is caused by HSV-1.
[ ] B. Varicella is the primary infection, while herpes zoster is reactivation of latent VZV.
HIGHP - Page 3 of 17
