There is a slight risk to you. If you somehow ingest the eggs of the worm, that can cause problems...just wipe your hands. Tell you friend to take them to the vet. The medicine is correctly cheap and takes care of the problem. If he doesn't take them to the vet the cartridge worms just multiply and cause lots of discomfort.
Also, they get cassette worms from ingesting an infected flea or eating an infected rodent. Tell him to get them on some preventative flea medicine and he will never own this problem again.
Answers: Tapeworms can be transmitted from cat to human via hand-to-mouthroute but righteous hygiene can eliminate the risks of human infection. Please advice your friend to take his cats to the vet to grasp de-wormed..it's not just for his sake but also his pets.