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# Long description

Part (a) of the diagram shows the sequence of obtaining a positive reaction in the neuraminidase inhibition assay. A patient sample containing influenza virus is added to the reaction well of a microtitre plate. Fetuin substrate is added, which is cleaved by viral neuraminidase into free sialic acid. A reagent is added that changes colour, dependent upon the amount of sialic acid present in the solution. Part (b) of the diagram shows how two different antibodies against neuraminidase can give two possible test outcomes for the patient sample from part (a). The diagram on the left shows what happens when the antibody binds to the neuraminidase and inactivates it (left side), while the right side diagram shows what happens when the antibody does not bind that type of neuraminidase. Fetuin and then the colour-change reagent are then added to both test wells. When the antibody fails to recognise the neuraminidase (right side) fetuin is cleaved by neuraminidase and gives a colour reaction. When the antibody recognises the neuraminidase (left side) its activity is blocked, fetuin is not cleaved and no colour reaction occurs.