This question is based on a confusion about the term "original sin." There are at least two concepts to which this term can refer, and they don't imply each other. From the New Advent Catholic Encyclopedia:
Original sin may be taken to mean: (1) the sin that Adam committed; (2) a consequence of this first sin, the hereditary stain with which we are born on account of our origin or descent from Adam.
From the earliest times the latter sense of the word was more common, as may be seen by St. Augustine's statement: "the deliberate sin of the first man is the cause of original sin" (De nupt. et concup., II, xxvi, 43). It is the hereditary stain that is dealt with here. As to the sin of Adam we have not to examine the circumstances in which it was committed nor make the exegesis of the third chapter of Genesis.
Your question assumes that both meanings are tied to each other, which is a position that Catholicism does not hold.
Catholics which do not hold to a literal Adam and Eve would also not hold to a literal original sin in the first sense mentioned in the encyclopedia above.