EDIT: Ignore everything I just said. I must have seriously misunderstood something in the card description and made an entire post about it. Epic derp. Apologies.
EDIT2: I was right the first time, and to summarize what I said before I deleted it, its a bit too powerful if it increases in attack each time but still spawns on your side of the field. My original suggestion was that the Tapeworm should spawn on the side of the field of the creature it killed, to make it more of a double edged card, and add more depth to the strategy instead of just repeatable, growing virus.