Influenza A, B, and C viruses are the members of the Orthomyxoviridae family. Which of the following type changes its antigenic properties in a lesser degree?

Influenza A, B, and C viruses are the members of the Orthomyxoviridae family. Which of the following type is antigenically stable?

1

2

RNA genomes of Influenza A and B viruses occur as 8 separate segments. However, Influenza C viruses contain 7 RNA segments. What gene is lacking in Influenza C?

Genetic reassortment is when a cell is

coinfected by two different viruses of a given type, mixtures of parental gene segments may be assembled into progeny virions. This may result in sudden changes in viral surface antigen. What is the nature of the genome of the virus that causes this?

This is a property resulted from the genetic reassortment made by the virus that explains the epidemiologic features of influenza and poses significant problems for vaccine development.

Influenza viruses are relatively hardy in _____ and may be stored at 0-4 degrees Celsius for weeks without loss of viability

Influenza viruses are susceptible to lipid solvents, protein denaturants, formaldehyde, and irradiation as this destroys their infectivity

Both infectivity and hemagglutination are more resistant to inactivation at ________ pH than at ______ pH.

Standard Nomenclature

The standard nomenclature system for influenza virus isolates includes the following information:

Standard Nomenclature

Antigenic descriptions of the HA and the NA are given in parenthesis for type A. Which of the following is a correct example of this nomenclature?

Host of origin is NOT indicated for HUMAN isolates. Below is an example.

A/Hong Kong/03/68 (H3N2) – human isolate

A/swine/Iowa/15/30(H1N1) – swine isolate

Is this true or false?

So far, ______ subtypes of HA and _____ subtypes of NA in many different combinations, have been recovered from humans and animals.

While there are potentially 198 different influenza A subtype combinations, only 131 subtypes have been detected in nature. Current subtypes that routinely circulate in people are: ______ and A(H3N2)

This virus, scientifically called the ________ and more generally called “2009 H1N1” has continued to circulate seasonally ever since.

When humans are infected with influenza viruses that normally circulate in swine, these viruses are called ______ viruses. It is designated with a letter "v" (e.g. A(H3N2)v virus)

Of all the influenza viruses that routinely circulate and cause illness in people, ________ viruses tend to change more rapidly, both antigenically and genetically.

Influenza B is NOT divided into subtypes (unlike influenza A) but further classified into two lineages: B/Yamagata & ______

Influenza B generally changes more slowly in terms of their genetic and antigenic properties than influenza A viruses

True or false

(Structure)

Orthomyxoviruses contain 9 structural proteins where three large proteins (PB1, PB2, PA) are bound to the viral RNP. These three are responsible for RNA _______ & ________

(Structure)

It forms shell underneath the viral lipid envelope and is important in particle morphogenesis and is a major component of the virion

(Structure)

It associates with the viral RNA to form a ribonucleoprotein (RNP) structure 9 nm in diameter and assumes the helical configuration of the viral nucleocapsid

(Structure)

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(Structure)

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(Structure)

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(Glycoproteins: HA&NA)

• Spike-shaped trimer, activated by a protease

• Binds virus particles to susceptible cells (H for hattach, hold, hug)

• Major antigen against which neutralizing antibodies are directed

• Variability in HA: responsible for evolution of new strains and subsequent influenza epidemics

(Glycoproteins: HA&NA)

• Tetramer

• Has an enzyme activity

• Facilitates release of virus from infected cells

• Target of antiviral drugs (Zanamivir and Oseltamivir)

(Antigenic shift & antigenic drift)

1. Caused by accumulation of point mutations in the gene, resulting in amino acid changes in the protein

2. Sequence changes can alter antigenic sites on the molecule --> virions can escape recognition by the host’s immune system

3.Immune system DOES NOT cause the antigenic variation but rather functions as a selection force that allows new antigenic variants to expand --> A variant must sustain two or more mutations before a new, epidemiologically significant strain emerges

(Antigenic shift & antigenic drift)

Minor antigenic changes

(Antigenic shift & antigenic drift)

Major antigenic changes in HA or NA which result in the appearance of a new subtype

(Antigenic shift & antigenic drift)

1. Reflects drastic changes in the sequence of a viral surface protein, caused by genetic reassortment between human, swine, and avian influenza viruses

2. When shift happens, most people have little or no immunity against the new virus

3. Example: H1N1 2009 pandemic since it is a quadruple reassortant virus because individual gene segments of the virus originated from humans, birds, and Eurasian and North American swine.

(Antigenic shift & antigenic drift)

Influenza B and __ viruses DO NOT exhibit antigenic shift because few related viruses exist in animals. Influenza type B viruses change only by the more gradual process of antigenic drift

(Antigenic shift & antigenic drift)

Type ___ viruses undergo both antigenic drift and shift and are the only influenza viruses known to cause pandemics

(Antigenic shift & antigenic drift)

Internal proteins of the virus such as _____ do not undergo antigenic changes

(Antigenic shift & antigenic drift)

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(Antigenic shift & antigenic drift)

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