A very prominent virologist, you decided to play in your laboratory growing diff

Question

A very prominent virologist, you decided to play in your laboratory growing different viruses. You have one moderate, enveloped, negative strand RNA virus, and a naked, virulent, positive strand RNA virus. The moderate virus has a growth    cycle of 48 hours in vero cells, where the cytopathology is seen as the formation of polykaryocytes. The other virus does not seem to plaque or cause any detectable cytopathic effect in these cells, but it grows in rabbit kidney cell lines with a growth cycle of 8 hours. Unfortunately you do not have any other cell lines, except the vero line. During a recent meeting of the American Society of the Frustrated Virologists, you heard a paper describing how vero cells could be rendered permissive to infection with any    positive strand RNA virus. The trick was to coinfect or pre infect vero cells with a virus that would cause cell fusion    between normal and infected cells by inserting a viral glycoprotein (peplomere) rich in fucose in these membranes. Back in your fort, you decided to try this experiment. A productive viral infection with your moderate virus causes    massive cell fusion in vero cells 8 hours post infection. The same degree of cell fusion also occurs upon virus penetration if the multiplicity of infection is 10 or greater.

How many cells (%) will be productively infected with both viruses?

Explanation / Answer

Multiplicity of infection (MOI) is the average number of virus particles infecting each cell.
number of cells infected = Multiplicity of infection/plaque forming units (pfu) of virus
     Hence for determining the percentage of cells infected with viruses, we would need the MOI and pfu. However, given that the virus causes massive cell fusion in vitro cells 8 hours post infection and the same degree of cell fusion occurring upon virus penetration is 10 greater, which means the multiplicity of the virus increase 10 times after penetration. So the number of cells that will be productively infected would be approximately 50% of the cells be co-infected with the negative and positive strand virus.

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