9.4-MEASUREMENT OF VIRUS SIZES Flashcards
Primary method for direct viral size measurement
Electron microscopy
Technique relating sedimentation rate to viral size/shape
Ultracentrifugation
Size range of most animal viruses
20–300 nm
Smallest RNA virus family
Picornaviridae (4 kb genome)
Smallest DNA virus family
Parvoviridae (3.2 kbp genome)
Bacteriophage size range
10–100 nm
Staphylococcus bacterial cell size
~1000 nm (1 µm)
Viral protein protecting nucleic acids from nucleases
Capsid
Structural subunits forming viral capsids
Capsomeres
Symmetrical arrangements of viral capsids
Icosahedral/Helical
Envelope acquisition site in host cells
Cellular membranes (plasma/nuclear/Golgi)
Ether-sensitive viral component
Lipid envelope
Ether-resistant viral characteristic
Non-enveloped capsid
Viral glycoprotein function in entry
Receptor binding/membrane fusion
Viral genome classification basis
Nucleic acid type (DNA/RNA)
DNA virus with largest genome
Poxviridae (375 kbp)
RNA virus with largest genome
Coronaviridae (32 kb)
Segmented genome example
Orthomyxoviruses (Influenza)
Viral lipid envelope composition source
Host cell membrane during budding
Glycoprotein analysis method
X-ray crystallography
Viral protein initiating replication cycle
Uncoating proteins
Antigenic determinants on viruses
Surface glycoproteins/capsid proteins
Enveloped virus entry mechanism
Membrane fusion
Non-enveloped virus entry mechanism
Membrane disruption/lysis
Capsid symmetry in herpesviruses
Icosahedral
Helical nucleocapsid example
Rabies virus
Density gradient medium for purification
Cesium chloride/sucrose
S value correlation with viral size
Larger viruses = higher S (100–1000S)
Viral buoyant density range
1.35–1.4 g/cm³ (protein + nucleic acid)
Hydration impact on size measurements
Increases apparent size in solution vs. dried state
Freshly dispersed tissue cells with limited lifespan (≤20 passages)
Primary cell culture
Passaged primary cells retaining diploid chromosomes (≤50 passages)
Secondary cell culture (Diploid cell line)
Immortalized cells from tumors with abnormal chromosomes (unlimited growth)
Continuous cell line
Example of continuous cell line from cervical cancer
HeLa cells
Virus-induced cell changes (lysis
inclusions
Adsorption of RBCs to viral hemagglutinin on infected cells
Hemadsorption
PCR/sequencing to identify viral genetic material
Nucleic acid detection
Immunofluorescence/ELISA for viral antigens
Viral protein detection
Embryo death in eggs (e.g.
encephalitis viruses)
Pock/plaque formation in egg membranes (e.g.
herpesviruses)
Rapid cell destruction (e.g.
enteroviruses)
Fused multinucleated giant cells (e.g.
measles)
Swollen cells with nuclear clearing (e.g.
CMV)
Vacuolated cytoplasm (e.g.
SV40)
Viral replication factories visible under microscopy
Inclusion bodies
Intranuclear eosinophilic bodies in herpes infections
Cowdry type A inclusions
Cytoplasmic Negri bodies in rabies-infected neurons
Negri bodies
Intranuclear+cytoplasmic inclusions in measles
Warthin-Finkeldey bodies
Cytoplasmic Guarnieri bodies in smallpox
Guarnieri bodies
Liver cell Councilman bodies in yellow fever
Torres bodies
Rabies virus
Negri bodies (cytoplasm)
Herpes simplex virus
Cowdry type A (nucleus)
Variola virus (smallpox)
Guarnieri bodies (cytoplasm)
Cytomegalovirus (CMV)
Owl’s eye inclusions (nucleus)
Measles virus
Warthin-Finkeldey bodies (nucleus+cytoplasm)
What is the primary physical method using nucleic acid amplification to quantify viral genomes?
Quantitative PCR (qPCR)
Which serologic tests use radioactive or enzyme-linked antibodies to detect viral antigens?
RIA and ELISA
What rapid
low-cost assay measures viral hemagglutinin’s ability to clump red blood cells?
Which physical method directly visualizes and counts viral particles at high magnification?
Electron microscopy
What biological assay determines the virus dilution causing disease in 50% of inoculated animals/cells?
Endpoint dilution (ID₅₀) assay
Which widely used biological method quantifies infectious virus via clear zones in cell monolayers?
Plaque assay
What technique identifies infected cells by detecting viral antigens with fluorescent antibodies?
Immunofluorescence assay
Which egg-based method quantifies viruses through pock formation on membranes?
Chorioallantoic membrane (CAM) assay
What initial step concentrates viruses from body fluids using ammonium sulfate or PEG?
Precipitation purification
Which purification method separates viruses by size using sucrose gradients?
Density gradient centrifugation
What criteria confirm a particle as a virus (must show identical properties across preparations)?
Antigenic/biological consistency and host-independent nucleic acid
What laboratory hazard arises from homogenizing infected tissues or using broken glassware?
Aerosol exposure
Why is mouth pipetting prohibited in viral labs?
To prevent ingestion of infectious material
Which viruses retain infectivity after heating at 50-60°C for 30 minutes?
Hepatitis B virus and polyomaviruses
What salt stabilizes picornaviruses against thermal inactivation?
1M MgCl₂
Which viruses survive acidic conditions (e.g.
stomach pH)?
What radiation type most effectively inactivates viruses by damaging nucleic acids?
Ultraviolet (UV) light
How does ether susceptibility distinguish enveloped from non-enveloped viruses?
Enveloped viruses lose infectivity due to lipid membrane disruption
Which detergent solubilizes viral envelopes without disrupting capsids?
Nonionic detergents (e.g.
What chemical inactivates viruses by cross-linking nucleic acids while preserving antigenicity?
Formaldehyde
Why are viruses resistant to standard antibacterial antibiotics?
They lack bacterial targets (e.g.
Which sterilant is used for heat-sensitive equipment in virus labs?
Ethylene oxide gas
What skin disinfectant is effective against most enveloped viruses?
70% ethanol
Which vaccine inactivation method uses UV-activated nucleic acid-binding dyes?
Photodynamic inactivation (e.g.
How does qPCR overestimate infectious virus counts?
It detects non-infectious genomes/defective particles[^1][^3]
What advanced method quantifies single viral particles via nanopore size detection?
Tunable Resistive Pulse Sensing (TRPS)[^1]
Which ELISA variation offers highest specificity for viral antigen detection?
Sandwich ELISA[^1][^2]
What is the key limitation of hemagglutination assays?
Low sensitivity for low-titer samples[^2][^8]
Why do chemical/physical methods fail to distinguish infectious from inactivated viruses?
They detect viral components (protein/DNA) indiscriminately[^3][^5]
Which biosafety practice prevents cross-contamination during viral culture?
Use of HEPA-filtered biosafety cabinets[^4][^7]
What is the initial step where viral proteins bind to cell surface receptors like CD4 or sialic acid?
Attachment
Which penetration method involves the virus merging its envelope with the host cell membrane?
Membrane fusion
How do non-enveloped viruses like poliovirus typically enter host cells?
Direct penetration across plasma membrane
What process separates viral nucleic acid from capsid proteins after entry?
Uncoating
Where do most DNA viruses (e.g.
herpesviruses) release their genomes for replication?
Where do RNA viruses like picornaviruses typically replicate their genomes?
Cytoplasm
Which viruses require virion-packaged RNA polymerase to transcribe mRNA?
Negative-sense RNA viruses (e.g.
What mechanism allows HIV to enter cells via both CD4 and chemokine receptors?
Co-receptor-dependent entry (CXCR4/CCR5)
Which receptor does rhinovirus use to attach to respiratory epithelial cells?
ICAM-1
What is Epstein-Barr virus’s primary receptor for B-cell entry?
CD21 (complement receptor)
How do enveloped viruses like influenza acquire their lipid membranes?
Budding from host cell membranes
What occurs during morphogenesis of helical nucleocapsids?
RNA genome incorporation during capsid assembly
Why do non-enveloped viruses often cause cell lysis during release?
Lack of budding mechanism requiring membrane disruption
What determines the glycoprotein composition of viral envelopes?
Host cell membrane type used for budding
Which viral release method preserves host cell viability?
Budding (e.g.
What distinguishes (+)ssRNA viruses’ replication strategy from (-)ssRNA viruses?
Direct mRNA translation vs. requiring RNA-dependent RNA polymerase
How do DNA viruses exploit host cellular machinery?
Using host DNA/RNA polymerases for genome replication
What role do nonstructural proteins play in viral replication?
Facilitating genome replication/transcription (e.g.
Which step follows uncoating and precedes assembly in viral replication?
Genome replication/transcription
Why do retroviruses require reverse transcription before replication?
To convert RNA genomes into integration-competent DNA
What structural feature enables rabies virus to bind acetylcholine receptors?
Glycoprotein spikes (G protein)
How do picornaviruses protect their RNA during uncoating?
Partially uncoat while releasing RNA into cytoplasm
Which viral family requires nuclear export of mRNA for protein synthesis?
DNA viruses (e.g.
What triggers syncytium formation in paramyxovirus infections?
Fusion protein-mediated cell-cell membrane merging
How do segmented RNA viruses ensure genome packaging accuracy?
RNA-RNA interactions between genome segments
What advantage do lysogenic viruses gain by integrating into host DNA?
Latent persistence and vertical transmission
What are the primary person-to-person viral transmission routes exemplified by coronaviruses?
Direct contact (droplets/aerosols)
Which viruses spread via respiratory droplets/aerosols (e.g.
sneezing)?
What transmission route involves HPV and HIV through intimate contact?
Sexual transmission13
How do herpes simplex and EBV spread through non-sexual contact?
Hand-mouth/eye or mouth-mouth contact14
Which viruses transmit via contaminated blood products?
Hepatitis B
What is the primary route for enteroviruses and hepatitis A?
Fecal-oral transmission15
How do noroviruses spread via inanimate objects?
Fomite transmission (e.g.
Which animal-borne viruses transmit through bites?
Rabies virus (via saliva)15
How do hantaviruses spread from rodents to humans?
Aerosolized excreta in confined spaces15
What arthropods transmit flaviviruses like dengue?
Mosquito vectors (Aedes species)15
What is the human-arthropod cycle in viral transmission?
Direct transmission between humans and vectors (e.g.
What defines tangential infection in zoonotic cycles?
Accidental human infection from animal-arthropod cycles (e.g.
How does arthropod-to-arthropod transmission occasionally infect humans?
Spillover during vector feeding (e.g.
What environmental changes increase arbovirus emergence?
Urbanization disrupting arthropod habitats15
How do multiple sexual partners influence viral spread?
Facilitates HIV/HPV transmission through increased exposure13
Why do poor socioeconomic conditions exacerbate viral diseases?
Limited sanitation/healthcare access (e.g.
How does global travel contribute to pandemics?
Introduces endemic viruses to naïve populations (e.g.
What food-handling practice prevents hepatitis A transmission?
Proper cooking and avoiding fecal contamination65
How does healthcare accessibility impact viral control?
Reduces vaccine-preventable diseases (e.g.
What enables viruses to bypass host immunity?
Rapid mutation (e.g.
Why are public health measures critical for respiratory viruses?
Limits airborne/droplet spread through masking/distancing24
What vertical transmission method occurs during birth?
Intrapartum exposure to maternal fluids (e.g.
Which virus requires C-sections to prevent neonatal transmission?
Herpes simplex virus (active genital lesions)57
How does breastfeeding transmit viruses vertically?
Through infected breast milk (e.g.
What distinguishes airborne from droplet transmission?
Particle size (<5µm aerosols vs. >5µm droplets)12
Why are non-enveloped viruses resistant to desiccation?
Stable capsids survive on fomites (e.g.
What transmission route involves contaminated needles?
Percutaneous exposure (e.g.
