Antigens are molecules – proteins, peptides, carbohydrates, nucleic acids, lipids, or any other compound – that induce the production of antibodies and bind to antibodies. Parasites may present a great quantity and variety of antigens to the host that change with time as a consequence of maturation through different life-cycle stages. Parasitic antigens may be divided into several categories: diagnostic, protective, and pathologic. An antigen acts as immunogen when it is able to induce an immune response (immunogenicity). In general, different antibodies are produced to an antigen which bind to different epitopes. The hosts’ immune response depends on the presentation, quantity, and kind, of circulating antigen. Cross-reacting epitopes exist between the different stages of the same species and between different species of the same genus. In helminthinfections there is a high degree of cross-reactivity between species and genus. The antigens of...