The present invention relates to a method for preventing or treating virus and protozoa infection in a subject in need thereof comprising: orally administering to said subject an effective amount of a composition comprising a complex consisting of a starch binding protein (SBP)-tagged immunostimulatory protein and a SBP-binding matrix, wherein the immunostimulatory protein is from Ganoderma species. The present invention also relates to a method for inducing interferon-gamma production in a subject in need thereof comprising: orally administering to said subject an effective amount of a composition comprising a complex consisting of a starch binding protein (SBP)-tagged immunostimulatory protein and a SBP-binding matrix, wherein the immunostimulatory protein is from Ganoderma species. The present invention further relates to a method for improving feed intake, growth rate or feed conversion ratio in a subject in need thereof comprising: administering to said subject by oral administration or injection an effective amount of a composition comprising a complex consisting of a starch binding protein (SBP)-tagged immunostimulatory protein and a SBP-binding matrix, wherein the immunostimulatory protein is from Ganoderma species.