Virology

Question 1

Classification of viruses is made by:
A. Complement fixation serology
B. Electron microscopy
C. Nucleic acid composition
D. Cellular inclusion bodies

Answer 1

C. Nucleic acid composition

Note: True viruses have nucleic acid that is either RNA or DNA, and this serves as the basis for initial
classification. Members of these classes are further divided into groups that cause human disease based
upon the mode of transmission, tissues invaded, diseases produced, and antigenic characteristics.

Question 2

Which virus is the most common etiological agent of viral respiratory diseases in infants and children?
A. Respiratory syncytial virus (RSV)
B. Measles virus
C. Coxsackie A virus
D. Coxsackie B virus

Answer 2

A. Respiratory syncytial virus (RSV)

Note: RSV is the cause of croup, bronchitis, bronchiolitis, and interstitial pneumonia. Children under 1 year old who are hospitalized are the most susceptible group.

Question 3

The most common viral syndrome of pericarditis, myocarditis, and pleurodynia (pain upon breathing) is caused by:
A. Herpes simplex virus
B. Respiratory syncytial virus
C. Epstein–Barr virus
D. Coxsackie B virus

Answer 3

D. Coxsackie B virus

Note: Coxsackie A virus, Coxsackie B virus, and the echoviruses are most commonly implicated in myocarditis and other syndromes, including acute
cerebellar ataxia and hepatitis. Like poliovirus, infections are more common in the summer and fall
and gain entry through the gastrointestinal tract.

Question 4

Which of the following viruses is implicated along with Epstein–Barr virus as a cause of infectious
mononucleosis?
A. Cytomegalovirus (CMV)
B. Coxsackie A virus
C. Coxsackie B virus
D. Hepatitis B virus

Answer 4

A. Cytomegalovirus (CMV)

Note: CMV infection in a previously healthy individual causes a self-limited mononucleosis syndrome. CMV is an opportunistic pathogen that may produce lifelong infections and can cause a variety of diseases, including congenital and neonatal infection, hepatitis, pneumonia, and disseminated infection in immunocompromised patients.

Question 5

The most common causes of viral pneumonia in adults are:
A. Influenza and adenovirus
B. Hepatitis A and B viruses
C. Coxsackie A and B viruses
D. Herpes simplex and CMV

Answer 5

A. Influenza and adenovirus

Note: Influenza and adenoviruses are the main causes of respiratory infections, including the common cold,
tracheobronchitis, and pneumonia. Adenoviruses also cause conjunctivitis, keratitis, cystitis, and
gastroenteritis.

Question 6

Which virus belonging to the Reoviridae group causes gastroenteritis in infants and young children but an asymptomatic infection in adults?
A. Coxsackie B virus
B. Rotavirus
C. Respiratory syncytial virus
D. Rhabdovirus

Answer 6

B. Rotavirus

Note: Rotaviruses have been implicated in both nosocomial infections and epidemic gastroenteritis. Children 3–24 months old are most commonly affected. Diarrhea begins after an incubation period of 3 days, lasts for 2–10 days, and is associated with vomiting and dehydration. In immunosuppressed
children, rotavirus causes a chronic infection.

Question 7

A very small, single-stranded DNA virus that causes a febrile illness with a rash and is called the fifth childhood disease after rubeola, rubella, varicella, and roseola is:
A. Rotavirus
B. Adenovirus type 40
C. Coxsackie A virus
D. Parvovirus B19

Answer 7

D. Parvovirus B19

Note: Parvovirus causes a fever and characteristic “slapped cheek” rash in young children. Adults are usually
immune, but immunocompromised persons may exhibit an arthritis or anemia (the virus infects immature RBCs in the bone marrow).

Question 8

Hepatitis B virus can be transmitted by:
A. Acupuncture
B. Tattoos
C. Sexual contact
D. All of these options

Answer 8

D. All of these options

Note: Although the most common mode of transmission of hepatitis B is via needle puncture, it may also be
transmitted by other parenteral means, including sexual transmission and contact with contaminated
blood through broken skin or mucous membranes.

Question 9

Which virus has been implicated in adult gastroenteritis resulting from ingestion of contaminated food (especially shellfish) and water?
A. Norwalk-like viruses
B. Rotavirus
C. Hepatitis C virus
D. Coronavirus

Answer 9

A. Norwalk-like viruses

Note: Norwalk-like viruses are small RNA viruses that have been implicated in epidemics of community
gastroenteritis as well as sporadic infections. Unlike rotaviruses, which cause gastroenteritis in infants and young children, Norwalk-like viruses produce infections in all age groups.

Question 10

Which virus is associated with venereal and respiratory tract warts and produces lesions of skin and mucous membranes?
A. Polyomavirus
B. Poxvirus
C. Adenovirus
D. Papillomavirus

Answer 10

D. Papillomavirus

Note: The human papillomaviruses (HPVs) cause genital warts. Several strains, including HPV-6, HPV-11,
HPV-16, and HPV-18, are associated with cervical and vaginal neoplasia. Because the virus cannot be cultured in vitro, diagnosis is usually made using DNA probes. A diagnostic characteristic of infected cells is koilocytosis, a perinuclear clearing in the squamous epithelium accompanied by nuclear atypia.

Question 11

A clinical test used for the detection and identification of viral infections other than culture is:
A. Hemagglutination
B. Hemadsorption
C. Viral antigen detection
D. All of these options

Answer 11

D. All of these options

Note: In addition to serological tests for antibodies against the virus and DNA probes that identify viral DNA or RNA, the methods above aid in the rapid diagnosis of several viruses. Various species of animal RBCs are used for identification of viruses
that contain receptors that agglutinate the RBCs. Some influenza A and parainfluenza viruses may be detected only by hemagglutination or
hemadsorption. Testing for viral antigen in culture is used for detection of RSV, CMV, and varicella zoster.

Question 12

Which technique is used for the confirmation of infection with human immunodeficiency virus (HIV-1)?
A. Western blot (immunoblot) assay
B. Enzyme-linked immunosorbent assay (ELISA)
C. Complement fixation
D. p24 Antigen testing

Answer 12

A. Western blot (immunoblot) assay

Note: The Western blot assay is most often used to confirm a positive serological test of antibodies to HIV. A
sample is confirmed positive if antibodies are demonstrated against two of the three major regions
(env, pol, and gag). However, because the Western blot detects antibodies it may miss people in the window phase of infection, is not confirmatory for
neonatal infections due to the presence of maternal antibodies, and has a long turnaround time resulting
in loss of contact with the patient. For these reasons, the CDC is evaluating a new approach using a simultaneous test for antibodies to both HIV-1 and
HIV-2 and p24 antigen to screen for infection. Positives would be tested by separate immunoassays to identify whether the infection is HIV-1 or HIV-2. Samples testing negative for both of these would be tested by a nucleic acid amplification method such as PCR for viral RNA.

Question 13

A 13-year-old boy was admitted to the hospital with a diagnosis of viral encephalitis. History revealed that the boy harbored wild raccoons from
nearby woods. What is the best method to determine if the boy has contracted rabies?
A. Remove the brainstems from all of the raccoons and examine for cytopathic effects
B. Request immunofluorescent test for antibody on the saliva from all of the raccoons
C. Request immunofluorescent test for antigen in cutaneous nerves obtained by nuchal biopsy of the patient
D. Isolate the virus from the saliva of both the animals and the patient

Answer 13

C. Request immunofluorescent test for antigen in cutaneous nerves obtained by nuchal biopsy of the patient

Note: Using direct immunofluorescence, rabies antigen
can be detected in the cutaneous nerves surrounding the hair follicles of the posterior region of the neck
(nuchal biopsy) and in epithelial cells obtained by a corneal impression. Antibodies to rabies can be detected in the serum and CSF of infected persons within 8–10 days of illness; however, infection usually occurs several months before the onset of symptoms. Isolation of virus from the saliva of the patient may be accomplished by mouse inoculation or by inoculation of susceptible cell culture lines with subsequent detection by immunofluorescent
antibodies.

Question 14

A 65-year-old woman was admitted to the hospital with acute respiratory distress, fever, myalgia, and headache. Influenza A or B was suspected after ruling out bacterial pneumonia. Which of the following methods could be used to confirm influenza infection?
A. Influenza virus culture in Madin–Darby canine kidney
B. Hemagglutination-inhibition test for antibodies in the patient’s serum
C. Direct examination of nasal epithelium for virus using fluorescent antibody stain
D. All of these options

Answer 14

D. All of these options

Note: Influenza virus types A, B, and C may be grown and isolated in embryonated hen eggs or cell cultures
using Madin–Darby canine kidney (MDCK), rhesus monkey, or cynomolgus monkey kidney cells. Cell culture using MDCK cells is the most rapid technique, permitting identification within 1–3 days. The hemagglutination inhibition test can be used to titer antibody to influenza virus and to distinguish virus subtypes, if specific antiserum is available. Direct fluorescent and enzyme immunoassays using monoclonal antibodies to nucleoprotein antigens in infected nasal epithelium are used for rapid diagnosis of both influenza A and influenza B infections.

Question 15

The most rapid definitive diagnosis of a genital herpes simplex (HSV-2) infection in a 20-year-old man is made by which method?
A. Direct immunofluorescence test for viral antigen in vesicle fluid
B. Titer of serum and seminal fluid for antibodies to herpes simplex
C. Detection of antiherpes simplex in seminal fluid
D. Cell culture of vesicle fluid

Answer 15

A. Direct immunofluorescence test for viral antigen in vesicle fluid

Note: Direct immunofluorescence testing of vesicle (lesion) fluid for virus using fluorescein-conjugated antibodies is the most rapid method for diagnosis of genital herpes infection. Immunofluorescence
and immunoperoxidase methods are also used to distinguish HSV-1 and HSV-2. PCR and real-time PCR are more sensitive rapid methods for detection and identification. Viral cell culture is also very sensitive and may yield a positive result within 24 hours when fluid contains a high concentration of virus. Vero cells or primary human embryonic cells are inoculated with vesicle fluid and examined for cytopathic effects
(CPE), the most common of which are large “balloon” cells and multinucleated giant cells.

Question 16

A 20-year-old female college student complained of a sore throat and extreme fatigue. The physician noted lymphadenopathy and ordered a rapid test for infectious mononucleosis antibodies that was negative. Bacterial cultures were negative, as were serological tests for influenza A and B, HIV-1, CMV, hepatitis B, and antistreptolysin O. What would be the next line of viral testing to establish a diagnosis?
A. Herpes simplex
B. Rubella
C. Epstein–Barr
D. West Nile

Answer 16

C. Epstein–Barr

Note: Epstein–Barr virus serological testing for IgM-VCA (viral capsid antigen) during the acute phase
would be indicated because testing for infectious mononucleosis antibodies may or may not be positive. Patients who present with an infectious mononucleosis-like syndrome should be tested for both EBV and CMV. Both viruses cause the same symptoms during the acute phase of the illness.

Question 17

A 60-year-old male gardener from New York State was hospitalized with flulike symptoms and eventually diagnosed with encephalitis. While
working in his garden, he noticed several dead birds around his bird feeder. The region was known to be heavily infested with mosquitoes.
What is the most likely cause of his illness?
A. West Nile virus
B. Epstein–Barr virus
C. Parvovirus
D. Hantavirus

Answer 17

A. West Nile virus

Note: West Nile virus causes neurological diseases with meningitis and encephalitis at the top of the list.
The animal reservoirs are birds, with humans being accidental hosts. Transmission of West Nile virus is
from mosquito to bird. The primary site of infection for Norwalk and rotavirus is the gastrointestinal area
and for hantavirus the pulmonary sector.

Question 18

A 30-year-old male patient who was a contractor and building inspector in the southwestern United States complained of difficulty breathing
and was admitted to the hospital with severe respiratory disease. The physician noted a high fever and cough. Two days before, the patient
had inspected an old warehouse, abandoned and infested with rodents. The patient was given intravenous antibiotics, but 2 days into therapy
the pneumonia worsened and he developed pulmonary edema. Which organism should be suspected of causing his illness?
A. Hantavirus
B. Rotavirus
C. West Nile virus
D. Norwalk-like virus

Answer 18

A. Hantavirus

Note: Hantavirus is transmitted by a rodent host, the deer mouse, and is endemic in the southwestern
United States. The name of the hantavirus responsible for outbreaks in this region is the Sin Nombre virus.
Breathing in excrement from the mouse is the most common route of infection, and the lung is the site
of initial infection. Diagnosis is usually made using an IgM ELISA assay.

Question 19

A 3-year-old female was admitted to the hospital following a 2-day visit with relatives over the Christmas holidays. Vomiting and diarrhea left the child severely dehydrated. No other members of the family were affected. All bacterial cultures proved negative. A stool sample should be tested for which virus?
A. CMV
B. EBV
C. Hepatitis D
D. Rotavirus

Answer 19

D. Rotavirus

Note: Rotavirus is one of the most common causes of gastroenteritis in infants and young children (6 months to 2 years old). Vomiting and diarrhea are also common symptoms of Norwalk virus infections, but the prevalence of rotavirus during the winter months and the lack of illness in other family members make rotavirus a more likely cause. Commercial availability of immunoassays for rotavirus makes its diagnosis easier to establish and rule out than infection with Norwalk-like
viruses.

Question 20

A 25-year-old male patient was diagnosed with HIV-1 by enzyme immunoassay, testing positive twice, and the diagnosis was confirmed by
Western blot testing. Which laboratory test should be performed prior to initiating antiviral therapy?
A. Quantitative plasma virus concentration (viral load testing)
B. Quantitation of CD4 lymphocytes
C. Phenotype/genotype resistance testing
D. All of these options

Answer 20

D. All of these options

Note: The decision to initiate antiviral therapy is based upon the presence or absence of symptoms, CD4
lymphocyte count, and the viral load. For example, treatment is usually withheld from patients with CD4 counts > 350/μL and viral load < 55,000/mL and is instituted in asymptomatic patients if the CD4
count is < 200/μL regardless of viral load. Treatment failure within the first year with three-drug regimens is 35%–45%, and drug resistance testing (genotype and/or phenotype testing) is recommended to identify drug-resistant strains prior to initiating
treatment.

Question 21

A 6-month-old male infant was hospitalized with a respiratory infection. He was diagnosed with apnea and bronchiolitis. Further testing revealed congenital heart disease. Bacterial cultures were negative for Streptococcus pneumoniae and Haemophilus influenzae. What further testing should be done?
A. Respiratory syncytial virus (RSV)
B. Rotavirus
C. Norwalk virus
D. HIV

Answer 21

A. Respiratory syncytial virus (RSV)

Note: Respiratory syncytial virus (RSV) is spread by large particle droplets such as dust and is one of the most
common causes of hospitalization for respiratory illness of infants less than 1 year old. RSV causes bronchiolitis, pneumonia, and croup in infants and
upper respiratory illness in children. It has also been found to cause nosocomial infection in nursing
homes. Diagnosis is made by EIA, fluorescent antibody (FA) staining, and cell culture.

Question 22

A young male hunter encountered a fox in his path during a walk in the woods. The fox was staggering but appeared nonthreatening. The man tried to avoid contact but was attacked and bitten on the leg. The bite broke the skin but was not deep.
Wildlife officials were unable to locate the fox for testing. What procedure should take place next for the hunter?
A. Spinal tap with CSF testing for rabies virus
B. Administration of hyperimmune antirabies globulin and rabies vaccine
C. Biopsy of the wound site
D. Throat culture and blood culture

Answer 22

B. Administration of hyperimmune antirabies globulin and rabies vaccine

Note: Rabies virus can be detected by FA staining and PCR testing. The virus replicates at the site of the bite and
penetrates the surrounding tissue, finding its way to the central nervous system. Since the source cannot be tested, the best course of action is to initiate postexposure prophylaxis with antirabies globulin and to immunize the patient with rabies vaccine.

Question 23

A 40-year-old female experienced a respiratory infection after returning home from a visit to her homeland of China. A rapid onset of pneumonia
in the lower respiratory area prompted the physician to place her in isolation. She was diagnosed presumptively with severe acute respiratory syndrome (SARS) and placed on a respirator. What type of testing should be done next to diagnose this disease?
A. Molecular technique and cell culture
B. Latex agglutination test
C. Blood culture
D. Complement fixation

Answer 23

A. Molecular technique and cell culture

Note: SARS virus was discovered in China in 2003. The virus belongs to the common cold group of coronaviruses, and is easily transmitted to health care workers having close contact with infected patients. It is the cause of a severe lower respiratory infection that can be fatal. Laboratory confirmation may be done by PCR testing that is available commercially, cell culture,
EIA, or IFA. Typically, PCR is used on two different specimen types or the same specimen type submitted at least 2 days apart. If both tests are positive, the infection is confirmed.

Question 24

A pregnant 25-year-old female with genital lesions delivered a premature newborn with complications. The baby tested negative for bacterial infection (cultures of blood and urine).
Antigen testing of the baby’s urine proved negative for group B streptococci and Streptococcus
pneumoniae. The mother tested negative for bacterial sexually transmitted diseases and for group B streptococci. The baby was treated with acyclovir and failed to survive. What was the most likely cause of death?
A. CMV
B. Human immunodeficiency virus
C. Respiratory syncytial virus
D. Herpes simplex virus

Answer 24

D. Herpes simplex virus

Note: Herpes simplex virus type 2 infections produce genital lesions. Infants born prematurely with
disseminated infection of HSV type 2 from HSV-positive mothers have a mortality rate of 50%–60%. Testing of pregnant women for antibody and Cesarean section delivery can prevent most neonatal HSV infections because the virus enters the fetus during the delivery process.

Question 25

A young father of two small children complained of a rash on the torso of his body. The children had been diagnosed with chickenpox and confined to their home. The father had experienced chickenpox as a child and knew he did not have the same rash as his children. What is the most
likely cause of the father’s rash?
A. Herpes simplex 1 virus
B. Varicella-zoster virus
C. Herpes simplex 2 virus
D. Epstein–Barr virus

Answer 25

B. Varicella-zoster virus

Note: Varicella-zoster virus is the cause of an infection with chickenpox. As an adult, the father is experiencing shingles, a reactivation of the virus.
The virus lies dormant in the sensory (dorsal root) ganglia of the spinal nerves, and its reactivation produces a nonweeping blisterlike rash on an
inflamed skin base that follows the path of the underlying nerves.

Question 26

The organs of a 65-year-old male were donated soon after a fatal auto accident. Three recipients of his corneas and kidneys died within weeks after receiving his organs. Which of the following viruses most likely caused the death of these recipients?
A. HIV
B. Rabies
C. Norwalk-like
D. Rotavirus

Answer 26

B. Rabies

Note: Transmission of rabies (rhabdovirus) occurs primarily from the bite of a rabid animal, but in 20% of human rabies cases there is no known exposure to rabid animals. Donor tissues are not routinely tested for rabies. Diagnosis is performed by fluorescent antibody staining of the infected tissues, and electron microscopy that shows the presence of bullet-shaped virus particles.

Question 27

While on a 7-day cruise to Vancouver and Alaska, a number of passengers reported to the ship’s medical staff complaining of vomiting and diarrhea. Which is the most likely virus to have
infected these mainly adult passengers?
A. Rotavirus
B. Parainfluenza
C. Respiratory syncytial
D. Norwalk or Norwalk-like viruses

Answer 27

D. Norwalk or Norwalk-like viruses

Note: Adult gastroenteritis caused by Norwalk and Norwalk-like viruses follows a 1–2 day incubation. Diagnosis is usually made on the basis of clinical criteria and confirmed by enzyme immunoassay, RT-PCR, or immune electron microscopy. Hepatitis E virus, also of the Caliciviridae family, also causes
gastroenteritis 1–2 days following exposure, but is not endemic in the United States and other developed countries.

Question 28

SITUATION: A patient tested positive for HIV-1 infection using a reverse transcriptase-polymerase chain reaction (RT-PCR) method. However,
1 week later a second blood sample was collected and sent to a reference lab that performed a confirmatory test by Western blot. The Western
blot test was negative. What best explains these results?
A. The samples for RT-PCR and Western blot were not from the same patient
B. RT-PCR is more sensitive for early detection
C. The RT-PCR result was falsely positive
D. The RT-PCR test detected HIV-2 and the Western blot is specific for HIV-1

Answer 28

B. RT-PCR is more sensitive for early detection

Note: Western blot is a test for antibodies to HIV, and sufficient antibodies are not usually present in the first 3–4 weeks of infection to cause a positive test. In some persons, antibodies do not appear until 3 months after initial HIV infection. RT-PCR detects viral RNA, and reduces the window phase of infection to approximately 1 week. Real-time PCR
tests for HIV-1 have 100% specificity at a cutoff of 20–40 copies RNA/mL. PCR is the preferred test for neonates because it avoids detection of maternal antibody, and is replacing Western blot as the confirmatory test of choice.

Question 29

SITUATION: A pregnant women was seen by her obstetrician with signs of flulike illness during her second trimester. NAT tests were ordered for
Toxoplasma gondii, rubella, cytomegalovirus, and herpes simplex 1 and 2. All test results were negative. However, after delivery, the newborn
exhibited signs of an infection and failed to survive. Which virus causes a 90% transplacental infection rate when found in the mother?
A. Hepatitis A
B. Hepatitis B
C. Hepatitis D
D. Hepatitis G

Answer 29

B. Hepatitis B

Note: Tests for toxoplasmosis, German measles, CMV, and HSV comprise a panel of infectious agents
known at a TORCH panel. The TORCH panel consists of serological tests for antibodies to these organisms, and has largely been replaced by more
sensitive NAT tests when infection is suspected. The “O” in TORCH stands for “other” and other viruses that cause transplacental infection such as
HBV and HIV should be considered.

Question 30

An immunocompromised patient was admitted to the hospital with a diagnosis of hemorrhagic cystitis. Which combination of virus and specimen would be most appropriate to diagnose a viral cause of this disorder?
A. BK virus—urine
B. Human papilloma virus—skin
C. Hepatitis B virus—serum
D. Epstein–Barr virus—serum

Answer 30

A. BK virus—urine

Note: The BK virus, a polyoma virus, is transmitted by direct contact with infected respiratory secretions. It has
tropism for the urinary system, and often causes a latent, asymptomatic infection in the kidney. However, in immunocompromised patients, the
virus is often implicated in renal and bladder infections. Kidney failure caused by BK virus is a significant concern in bone marrow and renal
transplant recipients.