A few comments:

1/ As you know, the parasites that were conclusive are microscopic. I presume there were no positives for worms?

2/ Flagyl is generally not considered to be anti worm but may have worm killing properties but would have to check. Flagyl is not without its side effects, there are sister drugs such as Tinidazole and Secnidazole that are in the same family but much less side effects.

3/ This has no resemblance of a worm which does not mean he does not have worms. Much of the hoopla about 'rope worms' is not based on credible Science for several reasons and I am sure I will face some opposition on this point.

4/ Generally Flagyl is not considered very effective, I would talk to your doctor about this, better yet see Dr. Cahill (Kevin Cahill NYC) if you can.