Week 12 Flashcards
Naked viruses
Naked viruses: nucleocapsid = [genome + capsid]
Enveloped viruses
How are they inactivated?
- Enveloped viruses: nucleocapsid + matrix/tegument + lipid bilayer + glycoprotein spikes
- Enveloped viruses can be inactivated via drying, detergents, pH, temperature
- This is because the lipid bilayer is required for infection of cells
- Enveloped viruses can be inactivated via drying, detergents, pH, temperature
DNA Virus Genome Types (5)
- Duplex, open ends: adenovirus and herpesvirus (open = say AH)
- Duplex, closed ends: poxvirus
- Duplex, closed circle: polyomarvirus and papillomavirus
- Duplex, inner strand incomplete: hepadnavirus
- Single stranded, linear: parvovirus
RNA Virus Genome Types (2)
- Coding strand = positive strand (same polarity as mRNA and functions as mRNA)
- Template strand = negative strand (opposite polarity of mRNA)
Capsid structures Types
- Capsid structures (protomer → capsomer → capsid)
- Icosohedral – rigid structure comprised that limits size of enclosed nucleic acid
- Helical – flexible structure that can accommodate any length of nucleic acid
Matrix/tegument
Proteinaceous layer – layer between capsid and envelope containing endogenous proteins/enzymes for viral assembly and initiating new infection
Envelope components
- Lipid bilayer derived from host cell membrane
- Glycoprotein spikes
DNA Virus
Capsid Structure?
Naked or Enveloped?
(NAME EXCEPTIONS TOO)
- DNA Viruses
- Capsid: icosahedral
- Exceptions: Pox
- Envelope: none
- Exceptions: Hepatitis B., Herpes viruses, and Pox
- Capsid: icosahedral
RNA Virus
Capsid Structure?
Naked or Enveloped?
(NAME EXCEPTIONS TOO)
- Capsid: icosahedral or helical
- Envelope
- Icosahedral: all naked
- Exceptions: Togaviruses and Flaviviruses
- Helical: all enveloped
- Exceptions: none
- Icosahedral: all naked
- Retroviruses have complex capsid and are enveloped
What are the general steps of virus life cycle?
- Virus Attachment Protein (VAP) binds to non-suspecting receptor on host PM
- Capsomere on naked virus
- Glycoprotein spike on envelope virus
- Virus penetration: release of nucleocapsid is dependent on pH changes → conformational change
- Endocytosis
- Fusion
- Uncoating of genome: release of genome from capsid
- Cellular Sites of Replication
Cellular Sites of Replication
RNA vs. DNA
(EXCEPTIONS?)
- RNA viruses: occurs in cytoplasm
- Exceptions: influenza and retroviruses (only virus to have 2 exact copies of its genome)
- DNA viruses: occurs in nucleus
- Exceptions: Pox and Hepatitis B
GENOME REPLICATION
RNA+ vs. RNA -
- Genome Replication: RNA-dependent RNA polymerase functions as replicase and transcriptase
- Positive Strand Virus: positive strand codes for mRNA to make proteins, one of which is an RNA poly → positive strand acts as template to make negative strand → negative strand serves as template for mRNA and positive genome production
- Negative Strand Virus: negative strand acts as template to make positive strand → positive strand serves as mRNA and as template for negative genome production
- Comes with RNA-dependent RNA polymerase in the virion
Protein production in DNA viruses
Three regulatory classes?
- Immediate-Early: regulatory proteins
- Early: genome replication
- Late: structural proteins
Provide examples of how viruses alter cell functions and appearance, intracellular defenses, and viral countermeasures.
- Evelopment: budding process of enveloped viruses to exit infected cells
- Cytopathology: host cell may be destroyed in process of evelopment
- Intracellular defenses: cells release interferon to activate immune response against infected cell
- Viral countermeasures: interrupt interferon signaling or encode anti-apoptotic proteins
Permissive vs. Non-permissive
- Permissive cells: allow for complete viral life cycle including release of virus
- Non-permissive cells: do not allow the viral life cycle to complete
Virus-Cell Interactions (5 TYPES)
- Lytic infection – virus production with cell death
- Abortive infection – infection of non-permissive cells with no infectious virus production
- Persistent infection – long-term virus-cell association with cell survival
- Chronic: virus replicates
- Latent: no replication but some viral gene expression
- Recurrent infection: has latent and lytic periods
- Transformation: oncogenic conversion caused directly by viral gene activities
Tropism
Tropism – a particular disease may be caused by several viruses that have a common tissue preference
Virulence factors
Virulence factors – required for pathogenicity and/or survival in the host; may not include factors required for viral growth
Attenuation
Attenuation – loss of virulence factors
Explain the differences between local and systemic viral infections with respect to replication sites, target organs, and disease manifestations.
- Local infection – virus replication at site of entry and spreads to adjacent cells
- Systemic infection
- Entry into host → primary replication → primary viremia → secondary replication → secondary viremia → disease → shedding (transmission to new host/cell)
- Primary is low viral load
- Secondary is high viral load
What if primary site of infection is target site of virus?
- If primary site of infection is target site of virus, disease is shorter incubation
- If secondary site is target tissue, disease is longer incubation
Viral modes of transmission
- Self-inoculation
- Inhalation
- Breaks in skin or mucoepithelial membranes
Sites of Entry (6)
Defense Mechanisms?
- Oropharynx – viruses can enter via aerosols or saliva
- Defense mechanism: mucous
- Respiratory tract – viruses can enter via inhalation
- Defense mechanism: temperature and mucociliary transport system
- Upper RT: 32 degrees Celsius gives rise to common cold
- Lower RT: 37 degrees Celsius gives rise to adenovirus
- Defense mechanism: temperature and mucociliary transport system
- GI tract – viruses can enter through our food and drink
- Defense mechanism: bile salts degrade enveloped viruses
- Skin – viruses can enter through trauma
- Conjuctiva – viruses enters via direct inoculation
- Defense mechanism: tears
- Genitourinary Tract: viruses enter via sex
- Defense mechanism: mucous, pH, urine
How do viruses causes damage?
- Cell killing by virus replication – budding can cause cell lysis
- Oncogenesis – can convert cells into tumor cells
- Immunopathology – activation of immune system to cause disease symptoms
Provide examples of viral counter-measures against host defenses.
- Cross BBB (ABs cannot reach this area)
- Pass beneath tight junction (restrict access of immune response)
- Viruses make IL-10 homologue (immunosuppression)
NAME EACH TYPE
Describe different types of exposure to viruses and provide examples of viruses that are transmitted in each situation.
- Crowded living conditions – rhinoviruses, influenza
- Certain occupations – HBV, HCV, HIV, HPV
- Lifestyle – HIV, HPV, herpesvirus
- Daycare centers – measles, mumps, rubella, rhinoviruses, influenza, herpesvirus
- Travel – arboviruses, respiratory viruses
Explain how viruses commonly found in healthy individuals and animals can cause disease in humans.
Normal Flora
Normal Flora
Sites and Examples
Normal Flora
- Oropharynx and Mouth
- Adenoviruses and cytomegalovirus (CMV)
- Large Intestines
- Adenoviruses and enterovirus
- Urinary/Reproductive Systems
- Papillomaviruses
Explain how each of the following affects susceptibility and severity of viral disease: age, immune status, general health, geography, and time of the year.
- Age
- Children – susceptible because immunologically naïve and small size/physiologic requirements
- Elderly – susceptible to new viral infections and reactivation due to decline in immune response
- Immune status – immunosuppressed individuals are at risk
- General health – poor nutrition leads to compromised immune system
- Geography – population density can spread disease
- Time of year – individuals spend more time inside during winter so higher concentration of air droplets
Explain the differences between outbreak, epidemic, and pandemic.
- Outbreak – introduction of a virus into a new area with immunologically naïve population
- Epidemic – spread of virus to larger geographic region
- Pandemic – worldwide spread of virus
Define:
Saprophytic, Symbiotic, Parasite, Pathogen
- Saprophytic – feeds on dead or decaying matter
- Symbiotic – mutually beneficial relationship with host
- Parasite – lives on or in a host solely to benefit itself
- Pathogen – when the parasite harms its host, it is called this
How fungi differ from bacteria?
- Fungi are eukaryotic
- Major sterol in cell membrane of fungi is ergosterol
