[bigpooch]

You definitely have a call here and there is no doubt about
it. Your opponent would have likely raised before the draw
with two pair a small amount just to attempt to get heads
up with the limper in which case it is very likely he has a
draw that he completed. Also, straight draws are very
troublesome hands, especially in PL and you often see them
beaten by better complete hands after the draw. A raise of
any amount will clearly be -EV plus your opponent may not be
playing any straight draw (for example, he may muck small
straight draws since they have almost no chance of winning
by pairing although arguably he may play a hand like AKQJ).

Also, in this case, there is a slight chance if the limper
is a bad player that he may overcall with trips.