The present invention provides a method of reducing the quanitity of mucus in the respiratory tract of a subject with elevated levels of mucus in said respiratory tract. The method includes administering to the subject a compound or composition containing a therapeutically effective amount of a fusion protein comprising a sialidase or an active portion thereof and an anchoring domain. The therapeutically effective amount comprises an amount of the fusion protein that results in a reduction of the quanitity of mucus in the respiratory tract after administration of the compound or composition when compared to the quantity of mucus present prior to administration of the compound or composition.