Question 1

Influenza virus attachment – Identify the glycoprotein: In influenza (an enveloped orthomyxovirus), which surface protein primarily mediates attachment to host cell receptors?

Accepted Answer

Introduction: Successful viral infection begins with attachment to host cells. For influenza viruses, two major glycoproteins decorate the envelope: hemagglutinin (HA) and neuraminidase (NA). Distinguishing the primary roles of HA and NA is essential in understanding pathogenesis, antiviral targets, and vaccine design. Given Data / Assumptions: Influenza is an enveloped RNA virus with HA and NA spikes on its surface. Attachment requires recognition of sialic acid on host cell glycoproteins/glycolipids. The question asks which protein is responsible for attachment, not release. Concept / Approach: HA binds to terminal sialic acid residues (e.g., alpha-2,3 or alpha-2,6 linkages), initiating entry by receptor-mediated endocytosis. NA acts later to cleave sialic acid, facilitating virion release and preventing self-aggregation. Therefore, the correct attachment mediator is HA. Step-by-Step Solution: Step 1: Identify influenza surface proteins: HA and NA.Step 2: Match function: HA → receptor binding; NA → sialidase activity aiding virion egress.Step 3: Recognize that fimbriae/flagellae are bacterial structures, not viral.Step 4: Conclude hemagglutinin is the attachment protein. Verification / Alternative check: Vaccine strain naming (e.g., H1N1, H3N2) emphasizes HA subtype for antigenicity and receptor binding properties, underscoring HA’s role in attachment. Why Other Options Are Wrong: Fimbriae/Flagellae: present in bacteria, not in viruses. Neuraminidase: cleaves sialic acid to aid release and spread; not the primary attachment factor. M2 ion channel: involved in uncoating and pH regulation inside endosomes. Common Pitfalls: Confusing functions of HA and NA; assuming any surface protein must be for attachment. Final Answer: Hemagglutinin.

Question 2

Biological control of insects – Candidate virus family: Which virus family has received the most attention for development as biological control agents against insect pests?

Accepted Answer

Introduction: Biological control seeks environmentally friendly alternatives to chemical pesticides. Certain viruses specifically infect insects, offering species-targeted suppression with limited off-target impact. This question assesses awareness of the virus family most widely explored and deployed for insect biocontrol. Given Data / Assumptions: Biocontrol agents must be effective, host-specific, and safe for non-target species. Some DNA viruses naturally infect arthropods. Commercial formulations have been developed for forestry and crop protection. Concept / Approach: Baculoviruses (family Baculoviridae) infect insects (mainly Lepidoptera) and are renowned for their narrow host range and environmental stability as occlusion bodies. These features have made them the leading viral candidates for biological insect control in agriculture and forestry. Step-by-Step Solution: Step 1: Identify viral families known for insect infection: Baculoviridae stands out.Step 2: Recognize production as occlusion bodies (polyhedra) facilitates formulation and field stability.Step 3: Compare alternatives: reoviruses, iridoviruses, and poxviruses have been studied but are less prominent for commercial biocontrol.Step 4: Select Baculoviridae as the best answer. Verification / Alternative check: Multiple registered biopesticides are based on nucleopolyhedroviruses (a genus within Baculoviridae), validating their practical application and interest. Why Other Options Are Wrong: Reoviridae/Iridoviridae: studied but not the mainstay of commercial insect biocontrol. Poxviridae: include vertebrate pathogens like vaccinia; not primary insect biocontrol tools. Adenoviridae: primarily vertebrate hosts; not used for field biocontrol of insects. Common Pitfalls: Assuming any insect-infecting virus is equally used; overlooking the formulation advantages of baculoviral occlusion bodies. Final Answer: Baculoviridae.

Question 3

Where RNA viruses replicate – Cellular location: In general (with noted exceptions), replication of viral RNA genomes occurs primarily in which host cell compartment?

Accepted Answer

Introduction: Replication sites differ between DNA and RNA viruses and even among RNA virus families. Understanding the default cellular compartment for RNA genome replication helps predict drug targets, host interactions, and cytopathic effects. This question asks for the general rule, acknowledging there are exceptions. Given Data / Assumptions: Most positive- and negative-sense RNA viruses synthesize RNA in the cytoplasm. Some exceptions (e.g., orthomyxoviruses, bornaviruses, hepaciviruses for certain steps) exist. The stem requests the usual site, not a universal rule without exceptions. Concept / Approach: RNA-dependent RNA polymerases (RdRp) of many RNA viruses operate on membranous replication complexes derived from ER/Golgi/endosomes located in the cytoplasm. Influenza viruses represent a key exception because they replicate RNA segments in the nucleus, but they are not the norm for all RNA viruses. Step-by-Step Solution: Step 1: Recall canonical families (Picornaviridae, Flaviviridae, Coronaviridae, Togaviridae, Paramyxoviridae) replicate in cytoplasm.Step 2: Note exceptions: Orthomyxoviridae (influenza) uses the host nucleus for transcription/replication steps.Step 3: Evaluate organelles: mitochondria, lysosomes, peroxisomes are not general sites for viral RNA genome replication.Step 4: Conclude the best general answer is cytoplasm. Verification / Alternative check: Electron microscopy and biochemical fractionation localize viral replication factories to cytoplasmic membranes for most RNA viruses, supporting this generalization. Why Other Options Are Wrong: Nucleus: true for specific exceptions like influenza, not the general rule. Mitochondria/Lysosomes/Peroxisomes: not principal replication sites for most RNA viruses. Common Pitfalls: Overgeneralizing the influenza exception; confusing entry/uncoating with replication location. Final Answer: Cytoplasmic matrix (cytoplasm).

Question 4

Cytopathic changes – Name the structures: During many viral infections, intracellular structures form that can directly disrupt normal cell architecture. What are these structures called?

Accepted Answer

Introduction: Viruses reprogram host cells to replicate their genomes and assemble progeny. This often produces distinctive intracellular structures visible by light or electron microscopy. Recognizing and naming these structures is useful in diagnostics and pathology. Given Data / Assumptions: Many viruses produce accumulations of viral proteins, nucleic acids, and altered host components. Such accumulations may be nuclear, cytoplasmic, or both. These structures can be diagnostic (e.g., Negri bodies in rabies). Concept / Approach: The general term for these virus-induced structures is “inclusion bodies.” They may be acidophilic or basophilic, eosinophilic under H&E staining, and can represent sites of replication or assembly, or aggregates of viral components. Step-by-Step Solution: Step 1: Associate specific diseases with inclusions (e.g., cytomegalic inclusions, Cowdry A).Step 2: Distinguish inclusions from generic chromosomal abnormalities or non-viral structures.Step 3: Identify inclusion bodies as the umbrella term used across virology.Step 4: Choose “Inclusion bodies.” Verification / Alternative check: Histopathology texts consistently describe viral inclusions as characteristic cytopathic effects aiding etiologic diagnosis. Why Other Options Are Wrong: Prokaryotes: refers to bacteria/archaea, not intracellular structures. Chromosomal disruptions: nonspecific description, not standard terminology. Cytocidal bodies: non-standard term; cell death is a process, not a defined structure. Stress granules: host RNA-protein assemblies; not synonymous with viral inclusions. Common Pitfalls: Confusing specific named inclusions with the general category; assuming inclusions are always nuclear (many are cytoplasmic). Final Answer: Inclusion bodies.

Question 5

Protein-only infectious agents – Neurodegeneration: Which agent is associated with transmissible neurodegenerative diseases in livestock and humans?

Accepted Answer

Introduction: Transmissible spongiform encephalopathies (TSEs) such as scrapie in sheep, bovine spongiform encephalopathy in cattle, and Creutzfeldt–Jakob disease in humans are unusual infectious neurodegenerative disorders. The causative agent defies classical definitions of life and infection. This question probes recognition of the unique agent class involved. Given Data / Assumptions: TSEs show long incubation, spongiform neuropathology, and lack of inflammation. Agents are resistant to nucleic acid–targeting methods and many disinfectants. Transmission has been documented in experimental and some natural contexts. Concept / Approach: The prion hypothesis identifies the infectious agent as an abnormal, misfolded isoform of a host protein (PrP^Sc) that templates conformational change in normal PrP^C. Therefore, prions—not viruses, viroids, or hypothetical entities—are implicated in TSEs. Step-by-Step Solution: Step 1: Match TSEs with protein-only infectivity.Step 2: Exclude viroids (small circular RNA in plants) and virions (general term for virus particles).Step 3: Recognize “virino” as a speculative concept lacking consensus.Step 4: Conclude prions are the correct agents. Verification / Alternative check: Biochemical purification and resistance patterns support the proteinaceous nature of the agent; genetic studies link PRNP mutations to familial prion diseases, reinforcing the mechanism. Why Other Options Are Wrong: Viroids: plant pathogens; nucleic acid–based. Virions: any complete virus particle; not specific to TSEs. Virinos: hypothetical; not established. Satellites: subviral agents requiring helper viruses; unrelated to TSEs. Common Pitfalls: Assuming all infectious agents must contain nucleic acid; conflating prions with viruses due to transmissibility. Final Answer: Prions.

Question 6

Viroids – Molecular nature: Viroids, which cause several plant diseases, are composed of what type of nucleic acid?

Accepted Answer

Introduction: Viroids are the smallest known infectious agents, responsible for several economically significant plant diseases. Unlike viruses, viroids do not encode proteins. Understanding their molecular composition is key to distinguishing them from viruses and prions. Given Data / Assumptions: Viroids infect plants and replicate in host cells without coding for proteins. They are circular molecules with extensive base pairing and secondary structure. The question asks for the nature of the nucleic acid they contain. Concept / Approach: Viroids are composed of small, circular single-stranded RNA molecules, typically 250–400 nucleotides long. Their pathogenicity arises from RNA structure and host interaction, not from expressed proteins. Step-by-Step Solution: Step 1: Exclude DNA options because viroids are RNA-only agents.Step 2: Exclude protein-only agents (that would be prions).Step 3: Identify the correct form as ssRNA with circular topology and high intramolecular base pairing.Step 4: Select “Single-stranded RNA (ssRNA).” Verification / Alternative check: Molecular analyses and replication mechanisms (rolling-circle) validate viroids as small circular ssRNA pathogens of plants. Why Other Options Are Wrong: ssDNA/dsDNA: not consistent with viroid biology. dsRNA: some RNA viruses have dsRNA genomes, but viroids do not. Protein-only: describes prions, not viroids. Common Pitfalls: Confusing viroids with viruses due to similar names; assuming all infectious agents encode proteins. Final Answer: Single-stranded RNA (ssRNA).

Question 7

Hepadnaviruses (HBV) – Unique replication: Hepatitis B virus is a DNA virus that replicates its genome using which key enzyme activity?

Accepted Answer

Introduction: Hepadnaviruses, especially hepatitis B virus (HBV), possess a partially double-stranded DNA genome but replicate via an RNA intermediate. This replication strategy distinguishes them from typical DNA viruses and underlies the use of reverse-transcriptase inhibitors in therapy. Given Data / Assumptions: HBV genome: relaxed circular, partially double-stranded DNA. Replication involves pregenomic RNA (pgRNA) as an intermediate. The key step resembles retroviral reverse transcription. Concept / Approach: HBV encodes a polymerase with multiple activities: reverse transcriptase to copy pgRNA into DNA, RNase H to degrade RNA in RNA–DNA hybrids, and DNA-dependent DNA polymerase to complete the second DNA strand. The signature, however, is reverse transcription of an RNA intermediate. Step-by-Step Solution: Step 1: Identify pgRNA as the template for DNA synthesis.Step 2: Recognize reverse transcriptase activity as essential for copying RNA to DNA.Step 3: Understand supporting roles of RNase H and DNA polymerase activities within the HBV polymerase.Step 4: Choose “Reverse transcriptase.” Verification / Alternative check: Antiviral nucleos(t)ide analogs (e.g., entecavir, tenofovir) target reverse transcription, clinically validating the mechanism. Why Other Options Are Wrong: DNA-dependent DNA polymerase only: incomplete; ignores RNA intermediate. RNase H only/DNA ligase: accessory or unrelated to primary genome synthesis step. RNA-dependent RNA polymerase: used by RNA viruses, not HBV. Common Pitfalls: Assuming all DNA viruses replicate purely with DNA polymerases; overlooking HBV’s RNA intermediate. Final Answer: Reverse transcriptase.

Question 8

Host cell macromolecules during infection – Identify the exception: Virulent and nonvirulent (attenuated) viruses typically do all of the following during infection, except which one?

Accepted Answer

Introduction: Many viruses reprogram host biosynthesis to favor viral replication. Common outcomes include inhibition of host DNA, RNA, and protein synthesis—collectively called host shutoff. Distinguishing typical inhibitory effects from atypical stimulation clarifies how viruses commandeer cellular resources. This question asks for the option that is generally not a feature shared by virulent and nonvirulent strains. Given Data / Assumptions: Viruses commonly suppress host transcription and translation to prioritize viral gene expression. Some lytic infections degrade host DNA. Nonvirulent (attenuated) strains can still impose host shutoff mechanisms, though often less aggressively. Concept / Approach: Evaluate which action contradicts the typical viral strategy. While degrees vary by virus, stimulation of global host macromolecule synthesis is not a common shared feature; instead, viruses usually inhibit host macromolecular processes and redirect them toward viral synthesis. Step-by-Step Solution: Step 1: List common viral effects: inhibit host DNA replication, suppress host mRNA production, and shut off host translation.Step 2: Recognize some viruses encode nucleases or trigger pathways that degrade host DNA or mRNA.Step 3: Compare with “stimulate host macromolecule synthesis,” which runs counter to conserved host-shutoff strategies.Step 4: Select stimulation as the exception (i.e., what they may not do). Verification / Alternative check: Examples include poliovirus cleavage of eIF4G (translation shutoff), herpesviruses’ host shutoff proteins, and influenza endonuclease/NS1 activities—all reducing host macromolecular synthesis rather than increasing it. Why Other Options Are Wrong: Inhibit DNA/RNA synthesis: widely documented across diverse viruses. Degrade host DNA: observed in several lytic infections. Shut off translation: a recurring strategy to privilege viral mRNAs. Common Pitfalls: Interpreting “nonvirulent” as “non-replicating”; many attenuated strains still induce host shutoff to some degree. Final Answer: Stimulate host cell macromolecule synthesis.

Question 9

Classifying eukaryotic viruses – Key criterion: For viruses infecting eukaryotes, which characteristic is most important for formal classification schemes?

Accepted Answer

Introduction: Virus taxonomy integrates multiple attributes, but one overarching feature anchors classification for eukaryotic viruses: the chemical nature of the genome and structural components. Recognizing this helps interpret families, Baltimore classes, and diagnostic algorithms. Given Data / Assumptions: Viral genomes vary: DNA vs RNA, single- vs double-stranded, segmented vs non-segmented, positive vs negative sense. Structural proteins and envelopes also differ chemically. Taxonomy aims for evolutionary and mechanistic coherence, not only clinical features. Concept / Approach: The chemical nature of virion constituents—especially genome type and replication strategy—forms the backbone of formal classification (e.g., Baltimore system categories I–VII). Morphology and host range inform lower-level distinctions but are not the primary axis. Step-by-Step Solution: Step 1: Prioritize genome chemistry (DNA/RNA, sense, strandedness).Step 2: Incorporate envelope presence, capsid symmetry, and replication mode.Step 3: Recognize host preference and disease severity as variable phenotypes not reliable for taxonomy.Step 4: Choose the option emphasizing chemical nature. Verification / Alternative check: ICTV and Baltimore classification frameworks consistently center on genome chemistry and replication strategy for high-level grouping. Why Other Options Are Wrong: Host preference/Disease severity: epidemiologic or clinical traits, not fundamental taxonomy. Morphology alone/Physical nature alone: helpful but insufficient for accurate classification. Common Pitfalls: Overvaluing disease outcomes or host range; ignoring replication chemistry when thinking about taxonomy. Final Answer: Chemical nature of virion constituents (type of nucleic acid and related properties).

Question 10

Oncopathology – key definition: In cancers and malignant neoplasms, what is the term for the reversion of cells to a more primitive, less differentiated state accompanied by loss of normal architecture and function?

Accepted Answer

Introduction: A cornerstone concept in pathology is how malignant cells diverge from normal cells. One hallmark of aggressive malignancy is the loss of differentiation. This question checks your ability to recall the precise term for that loss of mature features in cancer cells. Given Data / Assumptions: We are dealing with vocabulary used in surgical pathology and oncology. The focus is the regression to a primitive, undifferentiated phenotype. No calculation is needed; careful term recognition is required. Concept / Approach: Anaplasia literally means “to form backward.” In tumors, anaplasia describes a loss of structural and functional differentiation of normal cells. It is reflected by pleomorphism, hyperchromasia, high nuclear-to-cytoplasmic ratio, prominent nucleoli, abnormal mitoses, tumor giant cells, and architectural chaos. Greater anaplasia usually correlates with higher grade and more aggressive behavior. Step-by-Step Solution: Identify what is being asked: loss of differentiation toward an immature phenotype. Map the definition to the standard term used in pathology. Recognize “anaplasia” as the specific word describing dedifferentiation in malignant neoplasms. Select the option that exactly matches this concept. Verification / Alternative check: Textbook grading schemes for carcinomas and sarcomas commonly list anaplasia as a criterion of poor differentiation. Histologic images with marked pleomorphism and bizarre mitotic figures exemplify anaplastic change. Why Other Options Are Wrong: Neoplasia – general new, uncontrolled growth; does not specify differentiation loss. Metastasis – spread to distant sites; not about cellular maturity. Oncogenic – refers to the capacity to cause tumors; not a morphologic descriptor. Dysplasia – disordered growth in epithelia, potentially premalignant but not necessarily fully undifferentiated. Common Pitfalls: Confusing dysplasia with anaplasia; dysplasia can be reversible and graded, whereas anaplasia denotes frank malignant dedifferentiation. Final Answer: Anaplasia.

Question 11

Clinical virology – durable markers: After natural infection, which listed virus leaves markers that are reliably detectable long-term in most individuals, allowing past infection to be identified during adult screening?

Accepted Answer

Introduction: Serologic and molecular footprints of prior viral infection vary by virus. In public health and transfusion medicine, certain markers persist and are used to infer previous exposure. This item focuses on the virus for which routine adult screening relies on a durable marker of past infection. Given Data / Assumptions: We compare common human viruses: HBV, HSV, VZV, CMV. “Always detectable after infection” is interpreted as a robust, durable laboratory marker in typical adult practice. We prioritize markers widely used in clinical screening algorithms. Concept / Approach: For hepatitis B virus, anti-HBc (core antibody) of the IgG class usually persists for life after natural infection. Screening panels routinely leverage anti-HBc to establish prior exposure even when HBsAg has cleared and anti-HBs may vary. While herpesviruses also induce long-lived IgG, standardized adult screening for past infection typically emphasizes HBV core antibody as a dependable indicator across populations. Step-by-Step Solution: Identify viruses known for lifelong seropositivity. Recall that HBV anti-HBc IgG is a canonical, durable marker used in algorithms. Select the option that matches routine detection of past infection. Therefore choose Hepatitis B virus. Verification / Alternative check: Interpretation charts show that anti-HBc positive with HBsAg negative and anti-HBs positive indicates past resolved infection; even if anti-HBs wanes, anti-HBc IgG often remains, flagging prior exposure. Why Other Options Are Wrong: Herpes simplex virus – IgG often persists but is not a standard universal screening marker; detection is not uniformly performed to infer past infection. Varicella–zoster virus – IgG persists, yet adult screening programs commonly vaccinate or use exposure history; not the canonical “always-detectable” marker emphasized in algorithms. Cytomegalovirus – IgG persistence varies and is context dependent; not the standard marker for broad adult screening outside specific settings. None – incorrect because HBV provides a robust, lasting serologic footprint. Common Pitfalls: Equating “can be detected” with “routinely used marker.” Many infections leave IgG, but HBV anti-HBc is uniquely central to screening pathways. Final Answer: Hepatitis B virus.

Question 12

Oncogenic viruses – association check: Which virus has a well-established causal association with Kaposi's sarcoma in humans?

Accepted Answer

Introduction: Several human cancers are linked to specific viruses. Recognizing the correct pairing between tumor entity and etiologic virus is essential in pathology and epidemiology. Kaposi's sarcoma has a signature viral driver that should be memorized. Given Data / Assumptions: The neoplasm is Kaposi's sarcoma. Options list common oncogenic viruses. We seek the strongest, well-accepted causal link. Concept / Approach: Human herpesvirus 8 (also called Kaposi's sarcoma–associated herpesvirus, KSHV) is detected in virtually all forms of Kaposi's sarcoma (classic, endemic, iatrogenic, and AIDS-related). Viral genes promote angioproliferation and immune evasion, and seroepidemiology tracks disease prevalence. Step-by-Step Solution: Recall signature tumor–virus pairs taught in oncology. Match Kaposi's sarcoma with HHV-8/KSHV. Confirm no other listed virus is the principal causal agent. Select HHV-8. Verification / Alternative check: Immunohistochemistry for LANA-1 (latency-associated nuclear antigen) of HHV-8 is routinely positive in tumor cells, serving as a diagnostic test. Why Other Options Are Wrong: Epstein–Barr virus – associated with Burkitt lymphoma, nasopharyngeal carcinoma, some Hodgkin lymphomas. Human T-cell lymphotropic virus – linked to adult T-cell leukemia/lymphoma. Human papillomavirus – linked to cervical and anogenital cancers and subsets of head and neck cancers. Merkel cell polyomavirus – associated with Merkel cell carcinoma. Common Pitfalls: Confusing HHV-8 with EBV because both are herpesviruses; their tumor spectra differ. Final Answer: Human herpesvirus 8 (HHV-8).

Viruses in Eukaryotes Questions