“And let the leprosy of Naaman cleave to thee and to thy seed for ever.” This punishment took effect immediately. Gehazi went out from Elisha covered with leprosy as if with snow (cf. ex. 2Ki 4:6; Num 12:10). It was not too harsh a punishment that the leprosy taken from Naaman on account of his faith in the living God, should pass to Gehazi on account of his departure from the true God. For it was not his avarice only that was to be punished, but the abuse of the prophet's name for the purpose of carrying out his selfish purpose, and his misrepresentation of the prophet.
(Note: “This was not the punishment of his immoderate δωροδοκίας (receiving of gifts) merely, but most of all of his lying. For he who seeks to deceive the prophet in relation to the things which belong to his office, is said to lie to the Holy Ghost, whose instruments the prophets are” (vid., Act 5:3). - Grotius.)