importing shapefiles into AutoCAD map

I need to import a complex polygon shape file into AutoCAD (AutoCAD map 3D 2015).
I can import using Mapimport command, I can use the shp attributes to split into different drawing layers etc.

What I am having problems with is that all the shared boundaries are creating duplicate lines in the drawing. The reason I am importing into CAD is to create topologies and for this there must be a single line between adjacent polygons,, not 2 shared lines on top of each other. Is there any way to prevent the duplicate lines during import or is there a way to get rid of it after import. I imported polygons as closed polylines.