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39 Cards in this Set

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Are enveloped viruses more stable than uneveloped viruses?
No, because enveloped viruses are less stable they require a closer contact to be transmitted. Also, enveloped viruses are easily destroyed by ether.
What is the main component of virus envelopes?
Lipoprotein
Characteristics of unenveloped virus assembly
1. Few cell-associated virions are needed to launch infection --> short incubation period
2. Coutinious release of virions without gross cellular damage
3. Use of a modified cellular membrane (containing viral glycoproteins) for budding.
Compare the antigens for neutralizing antibody between enveloped and unenveloped virions
Enveloped - envelope glycoproteins

Unenveloped - nucleocapsid protein
Compare the sensitivity to ether between enveloped and unenveloped virions
Enveloped - sensitive to ether

Unenveloped - not sensitive to ether
The envelope of orthomyxovirus virions is made of...
lipoproteins + glycoproteins
Orthomyxoviruses:

Type of nucleotide
Number of nucleotide segments
Nucleocapsid
Virus-specific RNA polymerases in virions?
8 segments of (-) strand RNA
(each segment encode one of more unique proteins)
Helical nucleopcapsid
Contain its own polymerase to transcribe (-)RNA to (+)RNA which can be used as a mRNA
Compare RNA viruses with different different genomes
(minus-, plus- and ds-RNA)
First viral macromolecule synthesized in infected cell
RNA (protein-free) infectious?
RNA polymerase in virion
New viral RNA synthesis is totally dependent on synthesis of virus protein
(+)genome - proteins necessary for viral assembly, including polymerase and capsid; RNA infectious; No polymerase; Need virus proteins to begin its assembly
(-)RNA - first synthesize (+)stranded mRNA; RNA non-infectious itself; Contain polymerase; No
(ds)RNA - (+)mRNA; not infectious; no polymerase; not dependent on synthesis of virus protein to begin viral RNA synthesis
What are the two important antigenic molecules on the orthomyoviruses?
Hemagglutinin (H-glycoprotein): Required for virus adsorption to the host cell. H-abs can neutralize the virions. and are the most effective way of controlling infection.
Neuraminidase (N-glycoprotein): functions to release the newly formed virions from the host cell. N-abs can help slow the release of the virions and reduce the severity of disease and the chance of infection. BUT not as effective in blocking infection of new cells because does not neutralize virions.
How many nucleocapsid do orthomyxoviruses contain?
8 helical nucleopcapsids (each with unique RNA segment) in one enveloped virion.
Hemagglutination of orthomyxoviruses: What kind of antibody do we use for this clinical test?
Orthomyxoviruses agglutinate red cells by binding to RBC H receptors.
We inhibit the hemagglutination by adding antibodies against the H-antigen. (More H-abs added, less agglutination)
What is the most common disease caused by orthomyoxoviruses?
Influenza!
How many tpes of human influenze viruses are there?

Do they have different types of nucleocapsid?
There are three types of human influenza viruses (influenza A, B and C). Each type share the unique nucleocapsid antigen.

*There are many different strains in each type of influenza viruses
Which type of the influenza virus is the predominant cause of influenza?
Type A

Type C has a minor clinical significance. Influenza B epidemics are less severe and occur ever 3~6 years.
How often do minor and major epidemics of influenza A occur?
minor - 2 to 3 years
major - 10 to 30 years
What is the best available explanation of minor epidemics?
Antigenic drift
What is antigenic drift?
Minor variation in the gene for the H-antigen by mutation within existing RNA segments. This leads to a minor change in antigenic variant of H-antigen.
Can be made by mistakes of RNA replication, i.e. point or minor mutation.
Existing abs provide partial immunity since the mutated ags are similar enough to the old ags.
How can we best explai the major pandemics?
Antigenic shift
What is antigenic shift?
The major antigenic variation of H-antigen occurs so that existing abs in human population do not neutralize viral infectivity. May accompany a variation in N-antigen
What is the mechanism of antigenic shift?
1) Genetic recombination between human and animal influenza A strains - VERY frequent; pandemics in 1957 and 1968
2) Direct transmission of a swine or avian inflenza A virus into the human population- less likely because propagation method would be not well-suited to human; but might be a cause of 1918 pandemic
Explain the genetic recombination of viruses.
1) The first type of genetic recombination require classic mixing of genes on the same nucleotide segment - this is rare due to its requirement for close interaction of the two segments
2) Reassortment type of genetic recombination is more frequent because packging of a virion is a random process. This requires one cell to be infected by two different viruses. The chance of reassortment would be higher if the viral genome is composed of more than one segments.
Which classes of viruses are prone to genetic recombination?
Orthomyxoviruses (e.g. influenza viruses)
Reoviruses (e.g. rotaviruses)
What is phenotypic mixing?
Non-genetic interaction.
e.g. a Type I RNA is assembled into a type II capsomers or mixed type I and II capsomers.
This is transient!
How is influenza virus transmitted?
From person-to-person by coughs and sneezes.
Can directly infect the upper respiratory tract (no viremia-short incubation period)and infections often extend to the lower respiratory tract.
What are the symptoms of influenza diseases?
Fever, chills, aches

Possible complications: pneumonia, secondary bacterial infection, pneumococcus, staphylococcus
Pathogenesis of influenza diseases
Transmitted by coughs or sneezes
Involve destruction of ciliated epithelium in the respiratory tract.
Viremia is not common
Toxic components released from the site of local growth in the respiratory tract cause systemic symptoms (headache, muscle pains)
High risk group for influenza viruses?
Elderly population (>65 yo)
Infant population
What type of immunoglobulin is the most important factor in immunity and in recover from acute infection of influenza viruses?
Secreted IgA in the upper respiratory tract
Killed and polyvalent live-attenuated vaccine are available for influenza disease. To which age group each of the vaccines is recommonded?
The killed vaccines are recommended for the special risk groups, the elderly and the children, but the killed vaccines are 70% effective and may not induced IgA secretion.
The FluMist administered intra-nasal spray and is only approved for the age group of 5 to 49 yo.
Are there treatment to influenza disease?
Yes, amantadine and remantadine are effective against only influenza A by inhibiting its adsorption to the host cell.
Tamiflu and Relenza target neuraminidase (N-antigens) and are effective against both influenza types A and B. But it HAS TO BE used within 48 hours of the onset of the symptom.
How are paramyxoviruses different from orthomyxoviruses?
They have much in common except that paramyxoviruses have a single (-) stranded RNA segment whereas orthomyxoviruses have 8 segments of (-)stranded RNA. Paramyxoviruses cannot undergo re-assortment.
Do paramyxoviruses need a polymerase in the viron?
Yes!
What are 4 common diseases caused by paramyxoviruses?
Systemic infections:
Mumps
Measles
Non-systemic repiratory infections caused by repiratory syncytial virus and parainfluenza virus Type 1,2,3 and 4.
Which viruses of paramyxoviruses cause non-systemic respiratory disease?
Respiratory synctial virus
Parainfluenza Type 1,2,3,4
Mumps and measles
Systemic infection by mumps and measles viruses of paramyxoviruses
What are the characteristics of non-systemic paramyxoviruses?
Does not undergo major antigenic shift (as compared to repiratory infection caused by influenza viruses)
Many are subclinical
More severe in initial childhood infection
CROUP (acute laryngo-tracheo-bronchitis)

Characteristic
Risk group
Treatment
dyspnea
stridor (high pitched noisy inspiration)
glucocorticoid tretement in severe cases
Respiratory syncytial virus

Cause what types of infection?
Risk group
Vaccine?
Lower respiratory infection in infants and elderly population.
No vaccine availble
SARS (Severe acute respiratory syndrome)
SARS-associated coronavirus
Lower respiratory tract infection
Incubation day of 2 to 10 days