Brucellosis is a disease caused by facultative intracellular bacteria of the monospecific genus Brucella melitensis. The invention in one aspect is an immunogenic nucleic acid composition comprising DNA encoding Brucella melitensis Invasion Protein B, a polypeptide with at least 95% identity thereto, or an immunologically active fragment of either of these, and an adjuvant. In another aspect, the invention is a DNA vaccine composition comprising a plasmid vector having DNA encoding a polypeptide as recited above, in which said plasmid vector is adsorbed to a liposome. Other aspects of the invention include methods of inducing an enhanced immune response to Brucella infection in an animal, methods for the differential diagnosis in an animal of brucellosis and vaccination by an immunogenic nucleic acid composition having DNA encoding any of the above-recited polypeptides, and a kit for conducting said differential diagnosis methods.
