The influenza A virus uses a sialic acid as a receptor for cellular entry. The chemical composition of the specific type of sialic acid that the virus interacts with differs among animal species. The avian influenza virus attaches to a specific sialic acid that is present in fowl epithelial cells but absent in human cells, whereas the human influenza virus can only attach to the type of sialic acid present in human respiratory epithelium. When pig epithelial cells, which contain both types of sialic acid, are infected with the combination of avian and human influenza A viruses, some of the new avian influenza viral particles become capable of attaching to human cells. However, the progeny of this new strain of avian influenza virus is still unable to attach to human epithelial cells. Which of the following phenomena best describes the change in the avian influenza virus in this experiment?

Question

The influenza A virus uses a sialic acid as a receptor for cellular entry.  The chemical composition of the specific type of sialic acid that the virus interacts with differs among animal species.  The avian influenza virus attaches to a specific sialic acid that is present in fowl epithelial cells but absent in human cells, whereas the human influenza virus can only attach to the type of sialic acid present in human respiratory epithelium.  When pig epithelial cells, which contain both types of sialic acid, are infected with the combination of avian and human influenza A viruses, some of the new avian influenza viral particles become capable of attaching to human cells.  However, the progeny of this new strain of avian influenza virus is still unable to attach to human epithelial cells.  Which of the following phenomena best describes the change in the avian influenza virus in this experiment?

Quizplus · Accepted Answer

11ec160b_3879_5676_9249_ad74164aa1ee_MD0001_00 The acquisition of a new viral surface protein is often all that is necessary for a virus to infect a new type of host cell. In this scenario, avian and human influenza virus particles infect host pig cells; certain progeny avian virus particles obtain some of the surface components (eg, sialic acid receptors) of the human influenza virus, allowing the avian virus to infect human cells. This exchange is an example of phenotypic mixing, which generally occurs when a host cell is coinfected with 2 viral strains and progeny virions contain unchanged parental genome from one strain and nucleocapsid (or envelope) proteins from the other strain. However, because there is no change in the underlying viral genomes (no genetic exchange), subsequent progeny will revert to having only avian influenza type surface proteins and will again be noninfectious to human epithelium. (Choice A) Interference occurs when one virus inhibits replication and/or release of a second virus that is infecting the same cell. Simple interference would not result in a new phenotype for progeny. (Choice C) Reassortment refers to changes in genomic composition that occur when host cells are coinfected with 2 segmented viruses that exchange whole genome segments. When reassortment takes place in a cell coinfected by 2 viral strains, any genomic change in first generation progeny will also be present in subsequent progeny. (Choice D) Recombination may be defined as the exchange of genes between 2 chromosomes (double-stranded DNA molecules) by crossing over within homologous regions. As is the case with reassortment, any genomic change in the first generation progeny will also be present in subsequent progeny. (Choice E) Transformation is generally defined as naked DNA uptake by a prokaryotic or eukaryotic cell. In virology, this term may also describe incorporation of viral DNA into a host cell chromosome. Transformation alters the genetic composition of the host cell but typically causes no genomic change in progeny virions. Educational objective: Phenotypic mixing refers to coinfection of a host cell by 2 viral strains, resulting in progeny virions that contain nucleocapsid proteins from one strain and the unchanged parental genome of the other strain. Because there is no change in the underlying viral genomes (no genetic exchange), the next generation of virions revert to their original, unmixed phenotypes.

The Influenza a Virus Uses a Sialic Acid as a Receptor