Results from our study indicated that the CP-δ fusion protein plays a specific function in host cell entry during Orsay infection based on the following evidence: (1) Orsay δ forms pentameric fibers; (2) CP-δ is incorporated into viral capsid as a minor structural protein; (3) the δ portion of CP-δ forms a long projecting fibers with a globular head domain at the distal end; (4) disrupting the structural integrity of CP-δ results in non-viable virus mutants; and (5) the addition of recombinant δ to worm medium reduced Orsay infectivity. Here, CPD is linked to infection.