The present invention relates to parasitic helminth aromatic amino acid decarboxylase proteins; to parasitic helminth aromatic amino acid decarboxylase nucleic acid molecules, including those that encode such aromatic amino acid decarboxylase proteins; to antibodies raised against such aromatic amino acid decarboxylase proteins; and to compounds that inhibit parasitic helminth aromatic amino acid decarboxylase activity. The present invention also includes methods to obtain such proteins, nucleic acid molecules, antibodies, and inhibitory compounds. Also included in the present invention are therapeutic compositions comprising such proteins, nucleic acid molecules, antibodies and/or inhibitory compounds as well as the use of such therapeutic compositions to protect animals from diseases caused by filariids. The present invention also includes a method for detecting the presence of amino acid decarboxylases.