#$%^&*AU2017251766A120180517.pdf#####ABSTRACT The present specification relates generally to the field of immunization of a mammal against infection. Enabled herein is a method of immunizing a mammal against infection by Actinobacillus pleuropneumoniae or a related microorganism. Also taught herein is a method of preventing pneumonia in a mammal due to infection by Actinobacillus pleuropneumoniae or its relatives.