Parasitic worm therapy for allergy: is this incongruous or avant-garde medicine?

Helminth (worm) therapy has already been used in clinical trials associated with allergy. These were generally small scale, safety orientated trials of short duration, justified by epidemiological and experimental data indicating potentially beneficial immune modulation by some parasites. However, parasites by definition are disadvantageous to their hosts, and helminth infection in particular almost invariably induces an allergic phenotype, rendering this somewhat paradoxical therapeutic approach for allergy open to scrutiny. Is parasitic worm therapy for allergy incongruous medicine, or avant-garde medicine? In the present article, we assess the strength of evidence supporting the use of helminth therapy for allergy and critically appraise the trials already completed. Then, should this approach prove successful, we suggest strategies to improve the delivery of helminth therapy, and ways to discover immune response modifiers derived from worms.