In the original comic story of "The Purple Smurfs," it was an un-named Smurf (who will become Grouchy Smurf in "L'oeuf et les Schtroumpfs" or "The Egg and the Smurfs" in English) that was bitten by the fly (called the "Bzz Fly" in the comic; "Purple Fly" in the cartoon), not Lazy. Also, the diseased Smurf who painted himself blue and bit Papa Smurf was also an un-named Smurf, not Hefty.
Many of the more violent scenes in the comic version of "The Purple Smurfs" did not make this cartoon version, such as the Purple Smurfs actually biting their victims' tails, and Papa Smurf using his bellow to smack the jaw of a Purple Smurf while defending himself.
The original 1959 comic source of "The Purple Smurfs ("Le Schtroumpfs noirs" or "The Black Smurfs" in English) is the debut of Jokey who played a prank near the end of the story. He is the first Smurf other than Papa Smurf to be identified by name.
In the original comic version of "The Purple Smurfs" (titled "Les Schtroumpfs noirs" or "The Black Smurfs" in English) the bitten Smurfs were black-skinned. The color change in the cartoon version was done to eliminate any racist connotation.
At this point in the Smurf cartoon series' universe history ("The Purple Smurfs"), when Papa Smurf, being bitten by purple Hefty, says that the Smurfs will be no more, Baby, Grandpa, Wild, and Nanny had not yet shown up or been revealed.