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Flashcards in Microbiology 4: Viruses Deck (22):

All helical viruses have an _______?



What is acute (viral) infection?

Acute viral infections are characterized by either rapid recovery or rapid death (e.g. influenza or rabies).


What are envelopes?

Envelopes are basically pieces of cell membrane stolen from host cells. They are acquired during maturation through budding from cell membranes.
Proteins in the envelope are virally encoded:
• Glycoproteins – form projections known as spikes, needed to locate CD4 protein to get into the cell
• Matrix protein – layer on the inside of the envelope that provides added rigidity (only found in helical viruses)


Elaborate on the Icosahedron architecture

Icosahedral – spherical viruses are normally icosahedral (20 equilateral triangles arranged with 5:3:2 symmetry) and 12 vertices. This is a strong structure that can enclose a maximal volume.
Best way of producing a shell of equivalently bonded identical structures. Minimum free energy state.


What are the two types of virion architecture?

1. Spherical/Icosahedral
-Best way of producing a shell of equivalently bonded identical structures
-Minimum free energy state
-Strong structure that can enclose a maximal volume
2. Helix- Cylindrical shape (spiral staircase)


What are the mechanisms of production of disease?

• Cell death – cytocidal effect of virus, apoptosis, immune mediated

• Interference with the function of essential cells – hepatitis, myocarditis

• Body’s response to deal with cell damage – mucus production

• Local effects of the immune response – rashes (antibodies binding to virus generally)

• Systemic effects of the immune response – fever (INTERFERON released- leads to cytokines, chemokines, WBC's etc.)

• Triggering autoimmune response – post infectious encephalomyelitis


Elaborate on Helical viral structure?

several RNA viruses undergo self-assembly as a cylindrical nucleocapsid, where the RNA forms a spiral within the capsid structure. Each capsomere (capsid subunit) consists of a single protein, which protects the genome. All animal viruses with helical symmetry have a lipid envelope.


Provide insight into latency

latency occurs in nerve cells. The viral DNA is not integrated into the genome, limited expression of viral genes), and reactivates spontaneously or in response to specific stimuli (trauma, sunburn, stress).


What are the properties of naked viruses?

• Environmentally stable (temperature, desiccation, acid, proteases, and detergents). Hence, retain infectivity after drying, and can survive sewage treatment and in the GIT. Naked viruses are easily spread.
• They are non-hidden from the immune system so induce an immune response.


What is a virion?

Virions are extracellular v virus particles (it’s the virus when its not inside a cell!)

ƒ- Inert carriers of the genome outside of host cell, and take viral genomes from cell to cell, as well as protecting the genome in inhospitable environments.
-ƒ Assembled inside cells, from components of the virus. ƒ
- Do not grow or form by division (simply a product!).


What are characteristics of persistent viral infections?

• Symptom free periods followed by reactivation (e.g. herpes)
• Long symptom free periods followed by illness and death (e.g. HIV)
• Chronic, actively replicating viruses (e.g. HPV)


What are the properties of viruses?

• 25-350nm in size (average around 100nm)
• Totally dependent upon living cells for replication and existence
• Possess only one specie of nucleic acid either DNA or RNA (can be single stranded or double stranded) covered in protein
• Have a component for attaching and docking to cells
• Able to take over the host cell to propagate themselves


Viruses can be _____ or ________. Virion architecture can either be ________ or _____

Enveloped or naked
Spherical or helical


How does a virus enter the body?



They can enter through wounds on the skin, or via mucosal surfaces (the eyes, mouth, nose, urinogenital tract, lungs, GI tract.

They can also enter through direct entry into the blood . This includes through intravenous drug use, unsafe medical practices as well as insect vectors (mosquitos).

It can also occur through vertical transmission , which involves it being passed on from a mother to her baby.

Typically, the way a virus gets into the body is usually the way it get out!


Why are persistent infections important?

• Be activated and lead to acute disease (herpes)
• Cause chronic or progressive disease (Hep. B)
• Lead to the development of tumours (HBV)
• Confuse diagnoses if a persistent infection is detected as an incidental finding


What are the properties of enveloped viruses?

• Can be released by budding or cell lysis (do not always kill the cell to disseminate)
• They are environmentally sensitive (acid, detergent, desiccation, heat). Cannot survive in the GIT and must remain in moist environments. Hence, spread in large droplets, secretions and transplants
• They modify host cell membranes during replication (effectively steal it)
• Envelopes provide protection from host immune system(because it belongs to the cell)


Size of the icosahedral is relatively proportional to the _____?



How many viral families are there?

96 :)


In terms of incumbation periods, what can they indicate?

Short incubation period (less than a week)- Dealt with quickly and acutely

Medium incubation (roughly 2 weeks)- Effect multiple organs, give rashes, called systemic viruses.

Long incubation (multiple weeks 3-12)


What are viruses?

A virus is a cellular organism whose genome consists of nucleic acid, which can replicate inside host cells using host metabolic machinery to form a pool of components which assemble into particles called VIRIONS. Virions serve to protect the genome and to transfer it to other cells.

Intracellular – virus Extracellular - virion


All DNA viruses are ____?



What are the criteria used for classification of viruses?

• Type of nucleic acid
• Number of strands of nucleic acid and their physical construction
• Polarity of the viral genome
o Viral genome acts as mRNA are termed "positive stranded"
o Those where a transcript is made first are named "negative-stranded"
• Replication strategy
• Symmetry of the nucleocapsid
• Presence or absence of a lipid envelope