A change in the structure of an antigen on the surface of a disease-causing microorganism or virus (a pathogen) so that the host's immune system no longer recognizes the pathogen and must make new antibodies to recognize the changed antigens before the host can continue to combat the disease. As a result, the host cannot stay immune to the disease.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.

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