The major soil-transmitted helminths that infect humans are the roundworms, whipworms and hookworms. Soil-transmitted helminth
infections rank among the most important
neglected tropical diseases in terms of morbidity, and almost one billion people are still infected with at least one species. While
anthelmintic drugs are available, they do not offer long term protection against
reinfection, precipitating the need for
vaccines that provide long-term immunologic defense.
Vaccine discovery and development is in advanced clinical development for
hookworm infection, with a bivalent human hookworm
vaccine in clinical trials in Brazil and Africa, but is in its infancy for both roundworm (
ascariasis) and whipworm (
trichuriasis)
infections. One of the greatest hurdles to developing soil-transmitted helminth
vaccines is the potent immunoregulatory properties of these helminths, creating a barrier to the induction of meaningful long-term protective immunity. While challenging for vaccinologists, this phenomenon presents unique opportunities to develop an entirely new class of anti-inflammatory drugs that capitalise on these immunomodulatory strategies. Epidemiologic studies and clinical trials employing experimental soil-transmitted helminth challenge models, when coupled with findings from animal models, show that at least some soil-transmitted helminth-derived molecules can protect against the onset of autoimmune, allergic and metabolic disorders, and several natural products with the desired bioactivity have been isolated and tested in pre-clinical settings. The yin and yang of soil-transmitted helminth
infections reflect both the urgency for effective
vaccines and the potential for new immunoregulatory molecules from parasite products.