Viral Replication
What is the difference between susceptible and permissive cell lines?
Susceptible: virus enters and can infect, but does NOT replicate
Permissive: virus infects and completes cycle (replication)
True or False: enveloped viruses are less sensitive to disinfectants and more resistant to dehydration.
False, this is describing naked viruses. Enveloped viruses are less resistant in the environment and more sensitive to some disinfectants.
True or False: Antivirals should not be specific to viruses because it causes more side effects.
False!
Antivirals should be specific to viruses to render improved safety
Example: Acyclovir for Feline Herpesvirus 1 corneal ulcers
What are some host and environmental factors that can affect the outcome of a viral infection?
Host: age, immune status, genetic background, nutrition status, hormonal status
Environmental: overcrowding, poor ventilation, bad weather, low temp
True or False: Reassortment only occurs in segmented genomes
True, it is another way of evolution causing new strains. Also, they cause genomic shift.
What is a plasmid? When is it used?
Circular ring of DNA in viruses. It is used as an infectious clone if a virus doesn't grow in cell culture. It bypasses the need of receptors to enter, transcibe, and translate specific cell types.
What is a prion? What does it cause?
Bonus Q: how does it differ from a virus?
Abnormally folded protein resistant to proteases and accumulates into fibrils and plaques. They create vacuoles, appearing spongy under the microscope.
Can cause spongiform encephalopathies
Bonus Q: Prions don't have nucleic acids
How is HIV treated?
With an antiretroviral drug cocktail
List the ways viruses can enter the host (6) and describe how the host can protect itself, how infection occurs, etc.
Skin: breach in physical barrier or by vectors
Conjunctiva/mucous membranes: exposure, but MALT protect
Respiratory: ciliated epithelium, mucus secretion, lower temp
GI: gastric acid, bile salts; many are naked, so they are more resistant to this environment
Genitourinary: less frequently exposed, host flushes via urine, low pH
Iatrogenic: infected needles, blood transfusion
What are the 3 types of point mutations?
Insertion, deletion, and substitution
List template and product: Use (RNA/DNA) for (RNA/DNA) synthesis
DNA dependent DNA polymerase
RNA dependent RNA polymerase
DNA dependent RNA polymerase
Reverse transcriptase
DNA dependent DNA polymerase
---> Use DNA for DNA synthesis
RNA dependent RNA polymerase
---> Use RNA for RNA synthesis
DNA dependent RNA polymerase
--> Use DNA for RNA synthesis (occurs in cytoplasm)
Reverse transcriptase
--> Use RNA for DNA synthesis (occurs in nucleus)
What type of relationship do viruses have when comparing genomic sequence and how are they classified?
Evolutionary
Classified by predicting behavior
Why are many antiviral agents that interfere with viral replication also toxic to host cells?
A. Viruses use many of the host cell’s metabolic enzymes and replication machinery, so drugs targeting these processes can also disrupt normal cellular functions.
B. Viruses contain unique metabolic pathways that are similar to bacterial pathways targeted by antibiotics.
C. Viral capsids are structurally identical to host cell membranes, making it impossible for drugs to distinguish between them.
D. Viruses replicate independently of the host cell, requiring drugs that broadly destroy infected cells.
A. Viruses do not have their own metabolism, they are required to use the pathways of their host cells. They are required to be parasitic in order to multiply.
What is NOT true?
A. Rabies virus primarily infects the central nervous system, so its tissue tropism is for the brain.
B. Aerosolized respiratory secretions can travel longer distances than droplets, increasing the likelihood of infection.
C. Acute infections can cause phenotypic mutations
D. Free virus viremia is short lived because it is visible to the immune system
C
Which of the following statements about point mutations in viral genomes is correct?
A. Point mutations always result in the insertion or deletion of large segments of the viral genome.
B. Point mutations involve a change in a single nucleotide, which can alter viral proteins and potentially affect virulence or drug resistance.
C. Point mutations only occur in DNA viruses, not RNA viruses.
D. Point mutations always have no effect on the virus because the genetic code is redundant.
B
Describe how the steps of viral replication differ in naked and enveloped viruses during attachment, entry and release.
Naked - Attach via capsid. Enter via endocytosis and release by accumulating, then lysis
Enveloped - Attach via envelope. Enter via membrane fusion and release by budding or exocytosis
What is true about viruses?
A. Viruses are capable of independent metabolism and energy production.
B. Viruses contain both DNA and RNA in their genome.
C. Arboviruses transmit by and replicate in arthropods biologically
D. Viruses reproduce by binary fission similar to bacteria.
C
Example of a virus family would be togaviridae
What animal could antivirals NOT be used in?
A. A cat with Feline Herpesvirus
B. Valuable breeding animals where viral treatment is critical
C. Herefords (cattle) intended for human consumption
D. Zoo animals infected with a virus that uses reverse transcriptase
C. Antivirals CANNOT be used in food animals
Describe viremia and the difference between primary vs secondary
Viremia: virus present in bloodstream
Primary: initial spread of virus in blood from first site of infection
Secondary: infection of additional tissues results in virus entering circulation (systemic). Associated with crossing the blood-brain barrier. Part of the cycle of arboviruses and vector transmitted viruses.
Would a frameshift happen if you add 3 nucleotides? 2? 4? 6?
Bonus Q: Fill in the blank: The frame in which a protein sequence is translated is defined by the ______ ______
3 and 6: No
2 and 4: Yes
Mutations of a multiple of 3 do not cause.
Bonus Q: Fill in the blank: The frame in which a protein sequence is translated is defined by the start codon
List and describe the 10 steps of viral replication
1. Attachment - receptors become connected to complementary receptors (& co-receptors in susceptible cells)
2. Penetration - enter host cells cytoplasm
3. Uncoating - viral capsid opens and frees genome
4-8. Transcription (genome to mRNA) --> Translation (mRNA to protein) --> Replication (genome to copying itself)
9. Assembly
10. Release
Compare and contrast DNA and RNA viruses: Where do they replicate? Host range? Vaccines? Evolution?
DNA: Replicate in nucleus (species specific), narrow host range, vaccines quite effective at preventing disease, no evolution
RNA: Most replicate in cytoplasm, wide host range, jump host species, evolve fast resulting in spillover events, vaccines require frequent update due to mutation
True or False: Antiviral drugs are best suited for persistent infections. Why or why not?
Bonus Q: What type of viruses cause persistent infections
True, because there are more opportunities to interfere with viral replications compared to acute infections where the course may be too short
Bonus Q: Herpesvirus and retroviruses
Describe horizontal transmission vs vertical transmission. List some ways they can be spread.
Horizontal: One susceptible host to another.
Examples: Indirect (fomites), Direct (physical or sexual contact), Common-vehicle (fecal-oral), Airborne, Arthropod, Iatrogenic (Direct result of hospital staff), Nosocomial (In hospital), Zoonotic
Vertical: Parent to offspring
Examples: During gestation, during birth, after birth
A virologist is classifying a virus population. Which of the following correctly matches the viral classification with its definition?
A. Biotype – viruses distinguished by genetic sequence differences only
B. Serotype – viruses distinguished by antigenic differences recognized by antibodies
C. Genotype – viruses distinguished by growth characteristics in cell culture or host species
D. Variant – viruses distinguished only by disease symptoms in the host
B.
Biotype: distinguished by biological properties, such as differences in growth characteristics in cell culture, pathogenicity, or host range.
Serotype: distinguished by antigenic differences recognized by antibodies (surface antigens)
Genotype: distinguished by genetic sequence differences in their genome
Variant: differs from the original strain due to mutations