evidence: In the past, helminths were thought to simply suppress T-helper Type 1 (Th1) cells while inducing T-helper Type 2 (Th2) cells.[9] Rook points out that this hypothesis would only explain the regulatory effects of parasitic worms on autoimmune diseases caused by Th1 cells.[10] However, helminths also regulate Th2-caused diseases, such as allergy and asthma.[10] Rook postulates that different parasitic worms suppress different Th types, but always in favor of regulatory T (Treg) cells.[10] [...] Comparison with the hygiene hypothesis [edit]The Hygiene hypothesis postulates that decreasing exposure to pathogens and other microorganisms results in an increase of autoimmune diseases, according to Rook.[17] This theory and the theory that certain parasitic worms pacify the immune response are similar in that both theories attribute the recent rise of autoimmune diseases to the decreased levels of pathogens in developed countries. However, the Hygiene Hypothesis claims that the absence of pathogenic organisms in general has led to this.[17] In contrast, the parasitic worm theory only analyzes helminths, and specifically ones found to have a regulating effect.[17] [...] Multiple sclerosis [edit]In 2007, Jorge Correale et al. studied the effects of parasitic infection on multiple sclerosis (MS). Correale evaluated several MS patients infected with parasites, comparable MS patients without parasites, and similar healthy subjects over the course of 4.6 years.[8] During the study, the MS patients that were infected with parasites experienced far less effects of MS than the non-infected MS patients.[8]