Background: Trichuris suis ova (TSO), with the potential to modulate the human immune system, have been tested for therapeutic application in autoimmune and allergic diseases such as inflammatory bowel disease (IBD). Previous clinical studies were limited to European and American participants, whereas Asian populations have not been well documented. In this study, a clinical trial was conducted to examine the safety and tolerability of TSO administration among a healthy Japanese population. Methods: The study was a randomized, double-blind, placebo-controlled trial held at Jikei University Hospital, Tokyo. Twelve volunteers were stratified into three groups receiving different doses of TSO (TSO 1000, 2500, and 7500) and another into the control group. These cases were limited to healthy Japanese men aged over 20 years old. Single doses of medicinal TSO or placebo were given to three participants of each group. All participants were followed up to 56 days after ingestion. During the follow-up period, clinical practitioners checked each participant at the clinic at 7, 14, 28, and 56 days post-ingestion (dpi). Clinical symptoms were evaluated using questionnaire-based self-reporting, which participants filled at every visit. Blood samples were drawn at 7, 14, 28, and 56 dpi. Fecal samples were collected at 28 and 56 dpi. Results: During the study period, twelve healthy Japanese male volunteers were enrolled. All participants completed the follow-up period. No severe adverse events were observed during the study period in all groups. Three participants in the TSO 1000, 2500, and 7500 groups had mild to moderate abdominal symptoms, diarrhea, bloating, and appetite loss during the observation period. One participant in the placebo group presented with mild diarrhea. Microscopic examination identified no parasite ova in any fecal samples. Blood sample examination indicated elevated eosinophil count in several cases, especially in the groups with the higher dose of TSO. No extra-abdominal symptoms were present in all cases. Conclusions: Healthy Japanese people tolerated all doses of TSO without any severe adverse events. On the other hand, mild to moderate abdominal symptoms were observed in several participants. This study suggested that the medicinal use of TSO in Japan is relatively safe, and close follow-up is recommended for sustainable usage.
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