Human Challenge Model With ST-only Enterotoxigenic Escherichia Coli

Inclusion Criteria: * Provide written informed consent before initiation of any study procedures. * Healthy as judged by the Principal Investigator (PI) and determined by medical history, physical examination, and medication history. * Within 15 days of vaccination, have normal screening laboratories for white blood cells (WBC), hemoglobin (Hgb), platelets, absolute neutrophil count (ANC), sodium, potassium, chloride, bicarbonate, blood urea nitrogen (BUN), creatinine, alanine aminotransferase (ALT), C-reactive protein (CRP). * Demonstrate comprehension of the protocol procedures and knowledge of study by passing a written examination (passing grade is at least 80 percent). * Capable of understanding, consenting and complying with the entire study protocol. * Female subjects must be of non-childbearing potential, (as defined as surgically sterile or postmenopausal for more than 1 year), or if of childbearing potential must be practicing abstinence or using an effective licensed method of birth control (e.g., history of hysterectomy or tubal ligation; use hormonal or barrier birth control such as implants, injectables, combined oral contraceptives, some intrauterine devices (IUDs), cervical sponges, diaphragms, condoms with spermicidal agents, or must have a vasectomized partner) within 2 months of infection and must agree to continue such precautions during the study and for 30 days after the Day 56 study visit. Male subjects must agree not to father a child for 90 days afte…