Viewers have been watching as Diane's sister Val was told she could possibly have the virus, causing her to become distant to husband Eric, who may also have been subjected to the infection.Finding comfort and unaware of the dangers, Eric and Diane ended up spending the night together and therefore put Diane in danger of contracting HIV."It's a serious storyline," Elizabeth told This Morning's Eamonn and Ruth. "The main protagonists of course are Val and Eric and they are playing the story perfectly. It is perfectly pitched."Apparently there is a new demographic, historically we associate HIV with gay men, but now older women who are no longer worried about pregnancy are more at risk and in fact are contracting (HIV) more."I think in that sense it is a good storyline because it hasn't been covered before and the strength of soaps I always think is that if they have a storyline that is issue based it really draws a lot of people in."It is taking seriously and it is researched, we know all the details of what can and can't happen. It is a responsibility."This week on the soap it was finally confirmed to Val that she had the HIV virus, while Eric was given the all clear.But unable to deal with the guilt of sleeping with her sister's husband, Diane confessed, paving the way for some explosive scenes.Elizabeth said: "I don't know how it will affect them in the long term; I suppose when the story is eventually parked they will perhaps get on a bit better again."Emmerdale airs on UTV weekdays from 7pm.