The information provided here is not a replacement for a doctor. You shouldn't use it for the purpose of self-diagnosing or self-medicating but rather so you can have a more informed discussion with a professional TCM practitioner.
Because it is a herb specifically indicated to treat threadworm as can be seen on Chinaberry Root Bark's page.
Chinaberry Root Barks is a Cold herb that tastes Bitter. It targets the Spleen, the Stomach and the Liver.
Its main actions are: Kills parasites in the Intestines. Used topically for tinea and trichomonas vaginitis.
Roundworm Hookworm Pinworms Vaginal trichomonas infection Tinea Trichomonas vaginitis