Virology: Clinical Vignettes Flashcards
Questions
Answers
The capsid of a virus with helical symmetry is composed of
A. multiple identical copies of a single polypeptide molecule.
B. several polypeptides produced by sequential processing of a single large protein molecule.
C. several different polypeptides encoded by different open reading frames in the viral genome.
D. several different polypeptides generated by differential splicing of the same RNA transcript.
E. each of the above occurs and is characteristic of the specific virus family.
Correct answer = A. B, C, and D each occur in families with icosahedral symmetry, but helical capsids are composed of only one species of polypeptide, encoded by a single gene. In contrast, none of those with icosahedral symmetry have only a single polypeptide species.
The term eclipse period refers to
A. the period between epidemic outbreaks of diseases that occur in a cyclic pattern.
B. the period between recurrences of disease in individuals with latent virus infections.
C. the time between exposure of an individual to a virus and the first appearance of disease.
D. the time between infection of a susceptible cell by a cytocidal virus and the first appearance of cytopathic effects (CPE).
E. the time between entry into the cell and disassembly of the parental virus and the appearance of the first progeny virion.
Correct answer = E. C: This time is referred to as the incubation period. There is no specific term applied to the time periods described by A, B, and D.
The early genes of DNA viruses code primarily for proteins whose functions are required for
A. transcription of viral mRNA.
B. translation of the capsid proteins.
C. replication of the viral DNA.
D. final uncoating of the infecting virions.
E. processing of the mRNA precursors
Correct answer = C. Depending on the virus family, this may consist of a DNA polymerase and other enzymes directly involved in DNA replication or, alternatively, may be a product that stimulates the cell to produce all of the enzymes and precursors needed for DNA synthesis. A: Transcription for the most part is carried out by cellular RNA polymerase. B: Similarly, translation is done with the cell’s translation system. D: The poxviruses do code for proteins that are involved in completion of uncoating, but this is an exception. E: mRNA processing is accomplished by cell enzymes.
An important step in the mechanism proposed for oncogenesis by human papillomaviruses is
A. inactivation of a cellular regulatory gene by HPV integration into the coding region of the gene.
B. transactivation of a normally silent cellular oncogene by an HPV early protein.
C. reversal of keratinocyte differentiation caused by continued active replication and production of progeny HPV.
D. specific binding of certain HPV early proteins to cellular anti-oncoproteins.
E. induction of a specific chromosome translocation that results in activation of a cellular oncogene.
Correct answer = A. The appearance of the rash coincides with production of antibodies to B19, which occurs several days after the peak of viremia. B: Infection in immunodeficient individuals can lead to chronic, progressive depletion of erythrocyte precursors and severe anemia, but not rash. C: The host range of B19 is restricted to erythroid precursors, including those found in the fetal liver. Whereas this may be a factor in causing hydrops fetalis due to B19 infection of a pregnant woman, it is not related to the rash. D and E: Again, B19 is not known to infect other than erythroid precursor cells.
The characteristic spectrum of diseases caused by autonomous parvoviruses is related to the fact that they
A. integrate into a specific chromosomal site that disrupts an essential gene and leads to death of the cell.
B. require host cells that are actively progressing through the mitotic cycle.
C. infect only terminally differentiated cells.
D. code for an early protein that shuts off cellular protein synthesis.
E. increase the severity of the disease normally caused by their associated helper virus.
Correct answer = B. The diseases caused by the autonomous parvoviruses all result from the effects of killing multiplying cells that are essential for normal functions; for example, B19 specifically infects erythroblasts, leading to anemia in the fetus or in immunodeficient patients. A, C, D: Parvoviruses are not observed to integrate during the replicative cycle, they cannot replicate in terminally differentiated cells, and they do not shut off cell syntheses. E: By definition, the autonomous parvoviruses do not require a helper virus for replication.
The characteristic rash of erythema infectiosum is due to
A. virion/antibody immune complex formation.
B. bone marrow suppression caused by killing of erythrocyte precursors by B19 infection.
C. damage to the liver.
D. B19 infection of epithelial cells.
E. the inflammatory response to B19 infection of capillary endothelium.
Correct answer = D. The early proteins of both adenoviruses and papovaviruses required for immortalization and transformation of normal cells have been shown to bind specifically to cellular proteins p53 and pRb, which are important in maintaining regulation of the mitotic cycle. Interaction with viral proteins is believed to result in loss of their normal functions, as do the mutations that are commonly associated with spontaneously occurring cancers. A, B: Neither gene inactivation by integration nor transcriptional activation by an early protein has been observed. C: Virus replication occurs only in differentiated keratinocytes, but dedifferentiation does not occur. E: Multiple chromosome rearrangements are observed late in progression to malignancy, but none are specific for HPV-transformed cells.
The initial infection with human cytomegalovirus most commonly occurs
A. during early childhood, by exchange of body fluids.
B. in utero, by transplacental transmission from a latently infected pregnant woman.
C. by transfer of saliva between young adults.
D. by sexual intercourse.
E. as a result of blood transfusion or organ transplantation.
Correct answer = C. The specificity of acyclovir derives from the fact that it must be phosphorylated by the HSV or VZV thymidine kinase to be an active inhibitor of viral DNA synthesis. HCMV does not have a corresponding enzyme. A: HCMV develops resistance to those drugs that are effective, such as ganciclovir and cidofovir, after long term therapy, but because their mechanisms of action are different, mutants resistant to one are usually not resistant to the other. B: All herpesviruses code for their own DNA polymerase. D: In those cases where access is a problem for treatment of herpesvirus infections, direct inoculation of the drug has been done. E: Resistance to antiherpesvirus drugs has generally involved mutation of the enzyme interacting with the drug, not inactivation of the drug.
The cellular response typical of infectious mononucleosis caused by Epstein-Barr virus is due to:
A. stimulation of B-cell proliferation by the EBV early proteins synthesized in the infected cells.
B. proliferation of cytotoxic T cells responding to EBV antigens expressed on the surface of infected B cells.
C. a primary humoral immune response to the EBV infection.
D. macrophages responding to the death of EBV-infected cells.
E. activation of an oncogene resulting from a chromosome translocation in EBV-infected lymphocytes.
Correct answer = A. Depending on the population, up to ninety percent have antibody by adulthood. B: The most serious complications of infection are those resulting from transplacental transmission, but this is not the common mode of transmission. C and D: Transmission by kissing or sexual intercourse can occur, but most individuals have already been infected by this age. E: This mode of transmission has serious consequences in antibody-negative recipients, but most recipients had been infected at an earlier age. More common is reactivation of latent HCMV in recipients who have been immunosuppressed for purposes of transplantation.
Acyclovir is largely ineffective in the treatment of human cytomegalovirus infections because
A. HCMV exhibits a high rate of mutation in the target enzyme.
B. HCMV depends upon the host cell’s DNA polymerase for replication of its DNA.
C. HCMV lacks the thymidine kinase required for activation of acyclovir.
D. The tissues in which HCMV multiplies are largely inaccessible to the drug.
E. HCMV codes for an enzyme that inactivates the drug.
Correct answer = B. A: Polyclonal stimulation of B cells by EBV infection occurs, and results in appearance of the characteristic “heterophile antibodies,†but it is the CTL response that comprises atypical lymphocytosis of IM. C: EBV-specific humoral immune response is not related to lymphocytosis. D: B cells are not killed by infection with EBV. E: Whereas this is the process that results in EBV-associated Burkitt lymphoma, it occurs only years after the initial virus infection.
Killing of liver cells infected with hepatitis B virus is primarily caused by
A. shut-off of cellular protein synthesis.
B. intracytoplasmic accumulation of HBV antigen aggregates.
C. degradation of cellular mRNA.
D. attack by cytotoxic T lymphocytes directed against HBV antigens.
E. virus-induced aberrant chromosome rearrangements and deletions.
Correct answer = D. There is no evidence that HBV infection is cytocidal. Protein synthesis is not shut off, and mRNA is not degraded in infected cells. Accumulation of HBV proteins is not observed, rather they are actively exported. Whereas chromosome damage is observed in cells of primary hepatocellular carcinoma, it is not characteristic of nonmalignant infected liver cells.
The most common natural mode of transmission of infection with hepatitis B virus is via A. contaminated water supply. B. body fluids, such as urine and semen. C. respiratory droplets. D. direct contact. E. infected insect vectors.
Correct answer = B. HBV is found at high levels in all body fluids, which results in transmission from mother to newborn, from sibling to sibling, through sexual intercourse, and by infection by virus-containing blood. Contaminated water or food is the typical source of HAV and HEV infection.
Hepatitis delta virus is unique in that
A. infectivity requires an envelope protein provided by a helper virus.
B. it has an RNA genome that is replicated by a replicase supplied by a coinfecting helper virus.
C. its mRNA is transcribed by a transcriptase supplied by a helper virus.
D. the virion contains a reverse transcriptase provided by a helper virus.
E. it encodes a protein (HDAg) that replaces helper virus glycoproteins in the envelopes of helper virus particles.
Correct answer = A. The only function of the HBV helper is to supply the envelope. B: Genome replication requires a cell RNA polymerase, presumably modified by the HDV delta protein such that it can use the HDV RNA as a template. C: Transcription likewise depends on cell enzymes. D: The virion contains only the delta protein. E: HDAg is complexed with the RNA genome in the HDV virion and is not found in the HBV virion.
A company held an elaborate holiday dinner party for its 42 employees. Within three to four weeks, many of the banquet attendees complained of experiencing fatigue, fever, nausea, and dark urine, and were observed to be jaundiced. The group exhibited no bacterial infections in common. The employees who became ill had all eaten raw oysters at the party. The company doctor assayed a sample of the employees' blood for anti-hepatitis B antibodies, but all samples were negative for anti-HBsAg IgM. The causative agent consistent with this history is most likely: A. hepatitis A virus. B. hepatitis B virus. C. hepatitis C virus. D. hepatitis D virus. E. hepatitis E virus.
Correct answer = A. Hepatitis A is transmitted by the fecal-oral route and is most frequently acquired by eating contaminated shellfish or by contact with a carrier. The symptoms that were exhibited by the party-goers are consistent with liver damage caused by, for example, hepatitis. Hepatitis B infection is excluded because of the negative test for antibodies. Hepatitis C infection is acquired most commonly by IV drug users, patients on dialysis, and individuals obtaining tattoos. Hepatitis D infection occurs only in combination with hepatitis B infection. Hepatitis E is a major cause of enterically transmitted, water-borne hepatitis in developing countries.
Match the appropriate virus from the following list with the statement to which it most closely corresponds. Each virus can match one, more than one, or none of the statements. A. Hepatitis A virus (HAV) B. Coxsackie viruses C. Hepatitis C virus (HCV) D. Hepatitis E virus (HEV) E. Yellow fever virus F.Rubella virus
Intravenous drug users are at high risk for the virus
Correct answer = C. Until the recent development of tests for the presence of HCV in blood, HCV was an important cause of transfusion-associated hepatitis. IV drug users are one of several groups still at high risk for infection with this virus.
Match the appropriate virus from the following list with the statement to which it most closely corresponds. Each virus can match one, more than one, or none of the statements. A. Hepatitis A virus (HAV) B. Coxsackie viruses C. Hepatitis C virus (HCV) D. Hepatitis E virus (HEV) E. Yellow fever virus F. Rubella virus
Infection is caused by the bite of an infected mosquito
Correct answer = E. Yellow fever virus is an arthropod-borne virus, which is transmitted by the bite of an infected Aedes aegypti mosquito. The virus does not spread from person to person.
Match the appropriate virus from the following list with the statement to which it most closely corresponds. Each virus can match one, more than one, or none of the statements.
A. Hepatitis A virus (HAV) B. Coxsackie viruses C. Hepatitis C virus (HCV) D. Hepatitis E virus (HEV) E. Yellow fever virus F. Rubella virus
Predisposes to hepatocellular carcinoma
Correct answer = C. Unlike HAV, HCV infection has a strong tendency to lead to a chronic hepatitis and cirrhosis, often resulting after many years in hepatocellular carcinoma.
Match the appropriate virus from the following list with the statement to which it most closely corresponds. Each virus can match one, more than one, or none of the statements.
A. Hepatitis A virus (HAV) B. Coxsackie viruses C. Hepatitis C virus (HCV) D. Hepatitis E virus (HEV) E. Yellow fever virus F. Rubella virus
Causes congenital malformations
Correct answer = F. Infection with rubella virus is generally of little consequence to the adult. The exception is the pregnant woman, in whom rubella virus infection can result in congenital malformations in the fetus. The risk is highest in the first trimester. These malformations can affect the CNS, the liver, the heart, and the eye.
Current approaches to therapy of AIDS involve the use of multiple drugs because
A. it is not known which one will be effective.
B. mutants resistant to any one drug appear rapidly, but the chance for appearance of mutants resistant to all of them is small.
C. all inhibit the same step in replication, thereby increasing their effectiveness.
D. this is the most effective means of curing cells of integrated HIV genomes.
E. each tends to neutralize the toxicity of the others.
Correct answer = B. The major problem with chemotherapy of AIDS is the high mutation rate of the virus, leading to rapid appearance of mutants resistant to any single drug. By choosing drugs that act at different steps in the replication cycle or with different mechanisms of action, mutations in each of the affected proteins would have to occur in the same virus genome. The chance for this to occur is considerably lower than for either one individually. D: There is no way known to cure cells of their integrated genomes. E: Whereas these drugs do not neutralize each other’s toxicity, it is possible in some cases to use a lower dose of each of the drugs, decreasing the toxic adverse effects.
The “asymptomatic period” following the initial acute disease caused by HIV infection is characterized by
A. high levels of HIV replication in lymphoid tissue.
B. high levels of HIV replication in circulating T lymphocytes.
C. inability of the immune system to respond to antigenic stimuli.
D. absence of detectable HIV genomes or mRNA in circulating lymphocytes.
E. high titers of free virus in the blood.
Correct answer = A. During this period, a relatively large fraction of circulating lymphocytes can be shown to contain integrated HIV genomes, but a considerably smaller fraction have HIV mRNA, and virus replication occurs in relatively few cells. Infectious virus is largely confined to the lymphoid organs, although occasional bursts of viremia do occur, usually as the result of antigenic stimulation. The immune system retains its ability to respond to mitogenic stimuli generally, but there is some impairment of responses to specific antigens.
After infection of a cell by a retrovirus, synthesis of progeny genomes is carried out by
A. the DNA-dependent RNA polymerase activity of viral reverse transcriptase.
B. the retrovirus RNA-dependent RNA polymerase.
C. the host-cell DNA polymerase.
D. a host-cell RNA polymerase.
E. a complex of reverse transcriptase and a second virus protein that enables it to synthesize RNA rather than DNA.
Correct answer = D. Progeny virus RNA is synthesized by the same transcription process as that of cellular genes. A and E: Reverse transcriptase is involved only in the initial step, converting the infecting parental RNA genome into dsDNA. B: Unlike other RNA viruses, retroviruses do not encode an RNA-dependent RNA polymerase. C: The host cell DNA polymerase replicates the integrated provirus, but plays no role in synthesis of progeny.
An ornithologist was on a three-month trip to study several species of birds living in a rain forest in South America. On the tenth day of her trip, she was bitten on the hand by an unusually aggressive bat. The scientist applied a topical antibiotic ointment and continued her research. Four weeks later, the scientist lost feeling in her hand. She shortly began experiencing high fever, periods of rigidity, difficulty in swallowing liquids, drooling, and disorientation. Death followed rapidly. A postmortem biopsy of her brain showed the presence of Negri bodies. These symptoms are consistent with the woman having died of A. California encephalitis virus. B. hantaan virus. C. ebola virus. D. rabies virus. E. lymphocytic choriomeningitis virus.
Correct answer = D. Rabies virus is usually transmitted via the bite of an infected animal, and the woman’s symptoms are consistent with those of rabies. California encephalitis virus, transmitted by arthropods, causes meningitis and encephalitis. Hantaan virus is transmitted through aerosols formed from dried rodent excretions. This virus causes hemorrhagic fever and severe pulmonary infections. Ebola virus can be transmitted by an animal, but infection causes severe hemorrhagic fever. Lymphocytic choriomeningitis virus is a cause of viral meningitis and a relatively benign infection with little mortality. Humans are infected by inhaling contaminated aerosols, or eating food containing viral particles, or by exposure of open wounds to infected soil.
From 1918 until 1956, the only subtype of influenza observed in humans was H1N1. In 1957, H1N1 was replaced by H2N2. This is an example of A. viral interference. B. phenotypic mixing. C. antigenic shift. D. antigenic drift. E. viral transformation.
Correct answer = C. A marked antigenic change in the N protein, the H protein, or both is termed antigenic shift. In antigenic drift, there is also an antigenic change in one or both of these proteins, but the change is much less significant. With antigenic drift, although the H protein does change antigenically, H1 remains H1, for example.
The typical clinical syndrome associated with rotavirus infection is
A. acute gastroenteritis of young adults.
B. acute bronchiolitis of infants.
C. acute hepatitis.
D. nausea, vomiting, and diarrhea in infants and young children.
E. acute paralytic syndrome.
Correct answer = D. Rotaviruses infect and replicate in the gastrointestinal tract and typically affect infants and very young children. Although rotavirus infections are seen world-wide, there is significant mortality only in developing countries or in situations where good medical treatment (for example, fluid and electrolyte replacement), is not available.
Rotaviruses differ from polioviruses in that rotaviruses A. infect via the fecal-oral route. B. lack an envelope. C. can undergo genetic reassortment. D. do not contain any enzymes. E. have an icosahedral structure.
Correct answer = C. Because rotaviruses contain a segmented genome, infection of a single cell with two different rotaviruses can result in genetic reassortment and the emergence of a new viral strain with some genomic segments from one parent and the remaining genomic segments from the other parent. Rotaviruses do contain the enzymes required to synthesize viral mRNAs. A, B, D, E: There are no differences between polioviruses and rotaviruses in these characteristics.
The diagnosis of a rotavirus infection
A. can be made, in most cases, on the basis of the clinical presentation.
B. can be made on the basis of an increase in antibody titer.
C. is routinely made by electron microscopy of suitably treated stool samples.
D. can only be made on epidemiologic grounds (for example, if there is an epidemic).
E. must be made rapidly so that specific antiviral therapy is initiated as soon as possible.
Correct answer = B. The diagnosis of rotavirus infection is readily made by serology (that is, by demonstrating a rise in antibody titer). There are also several tests available by which rotavirus antigens can be demonstrated in the stool. Although the diagnosis can be made by electron microscopy, it is not a routine procedure. The clinical presentation is not sufficiently distinctive to make the diagnosis, and there is no specific antiviral treatment for rotavirus infections.
A patient with symptoms of Creutzfeldt-Jacob disease caused by eating contaminated beef would most likely exhibit which of the following
A. circulating antibodies specific for bovine CNS antigens.
B. DNA copies of the bovine infectious agent integrated into chromosomes of the patient’s diseased CNS tissue.
C. cytotoxic T lymphocytes directed against CNS-specific antigens found in both cattle and humans.
D. amyloid deposits that have bovine rather than the human amino acid sequences.
E. lack of any bovine-specific protein or nucleic acid or an immune response.
Correct answer = E. A and C: An important characteristic of the prion diseases is that there is no unique immune response to either the prion or to CNS antigens. B: A second distinguishing feature of these agents is the absence of a detectable nucleic acid genome. D: The amyloid deposits found in these diseases are composed of the diseased host’s proteins, and not of proteins from the source of the infection.
What degree of HSV resistance to acyclovir is seen in the US population?
Depend on the host
Asymptomatic shedding of HSV-2 occurs in what percentage of days out of a year?
4.30%
What antiviral drug is active against CMV?
Foscarnet
How are the asymptomatic HIV patients screen for CMV?
Eye exams every 6 months while the CD4 count is less that 50
What is the appropriate initial clinical management of AIDS?
Symptomatic therapy
The term “retrovirus” refers specifically to the presence of ____?
Reverse transcriptase
What measures can be protective against the acquisition of West Nile virus?
Mosquito repellant
What host factor is most strongly linked to increased morbidity and mortality of WNV encephalitis?
Older age
A 41 year old man presents to the ER with the sudden onset of anorexia, abdominal pain, nausea, and dark urine. He lives with his wife and 2 year old son who is in day care, neither of whom are ill. He works as a phlebotomist at your hospital and has been successfully immunized for Hep B. He drinks one glass of wine daily with dinner and denies IVDU. He takes no medications. On exam he is afebrile with obvious scleral icterus, mild jaundice, and RUQ tenderness. Labs show normal CBC and creatinine, AST, ALT, total bilirubin, Alkaline phosphataste. What is the most likely source of his infection?
Food
A healthy 35 year old woman is going to a remote village in Mexico for hiking in 2 weeks. She has no history of Hep A disease or vaccination. What strategy for prevention of Hep A is appropriate?
Both Hep A vaccine and serum Ig
What serologic marker shows immunity to HBV?
Anti-HBs
What HIV drug is also active against HBV?
3TC (lamivudine)
Ribavirin can treat certain hemorrhagic fever viruses as well as severe cases of RSV. It is also a mainstay of treatment of ___?
Hep C
A previously healthy 28 year old woman goes camping in New Mexico and develops a fever and sever pulmonary edema requiring intubation. She should be evaluated for ____?
Sin Nombre virus
A 29 year old confined to bed with headache, fatigue, and high fever most likely has?
Influenza
Which enzyme is inhibited by zanamivir?
Neuraminidase
What is a contraindication to influenza vaccination?
Allergy to eggs
What drug is active against influenza B?
Oseltamivir
Which of the following is not an RNA virus?
A. HIV B. Measles virus C. Rubella virus D. Hep B E. Hep C
Hep B
A woman in he 1st trimester of pregnancy is known to be rubella non-immune. She is inadvertently exposed to an active case of rubella through a coworker’s child. What is the most appropriate course of action?
Simultaneously determine rubella Ab titers on specimens obtained 2 to 4 weeks apart during pregnancy to determine risk to the fetus
What patients should not be offered a rubella vaccine?
The husband of a woman in her first trimester of pregnancy; neither parent has detectable rubella Abs.
A 25 year old medical student develops rhinorrhea, sneezing, nasal congestion, and mild sore throat, while her family medicine rotation in January. She has no fever, headache, or myalgia. What is the most likely cause of her symptoms?
Rhinovirus
A 23 year old man presents with acute onset of dysuria, gross hematuria, and suprapubic pain of 2 day duration. He has no fever. BP and creatinine are normal. UA shows 3+ hemoglobin, no leukocyte esterase. Microscopic exam of the urine shows numerous RBC’s of normal morphology. Routine culture is negative. CT scan of the abdomen is completley normal. His symptoms continue for 3 more days, and then spontaneously subside. What was the cause of his illness?
Adenovirus
T/F: OPV has the advantage of secondary immunization of non-immune contacts through the shedding of vaccine virus into the intestinal tract.
TRUE
