1.   The aetiology remains unknown, but much circumstantial evidence suggests that immunological mechanisms are involved in the pathogenesis.

2.   The cause of RP may be linked to the still unelucidated immunological mechanisms in inflammatory bowel disease that are clinically manifested as extraintestinal complications.

3.   Although this phenomenon has an immunological mechanism it is not necessarily associated with protection against reinfection since the larval challenge often develops to maturity.