CVD 38000: Study of Responses to Vaccination With Typhoid and/or Cholera

Inclusion Criteria: * 1\. Age 18 years and older * 2\. Already scheduled to undergo an EGD or colonoscopy for screening, surveillance, or a medically-indicated work-up at the University of Maryland Medical Center (main campus or Midtown) * 3\. Able to provide written informed consent prior to initiation of any study procedures * 4\. Healthy, as defined by considered fit to undergo outpatient elective EGD/colonoscopy by the evaluating health care provider Exclusion Criteria: * 1\. Pregnancy or nursing mother * 2\. Known coagulopathy or bleeding disorder preventing mucosal biopsy * 3\. History of Crohn's disease or ulcerative colitis * 4\. For Subjects undergoing lower endoscopy (colonoscopy) only: Surgical removal of the ileocecal valve or any part of the small or large intestine (non-complicated appendectomy will be considered eligible) * 5\. Allergic reaction to oral typhoid or cholera vaccine in the past * 6\. Immunosuppression from illness or treatment, including 1. immune-deficiency disorders such as Human Immunodeficiency Virus (HIV) or Acquired Immunodeficiency Syndrome (AIDS) 2. leukemia, lymphoma, or cancers (localized non-melanoma skin cancers which are deemed inactive should be considered eligible) * 7\. Receipt of any other vaccine two weeks prior to receipt of Ty21a or CVD 103-HgR * 8\. Positive urine pregnancy test (HCG) prior to colonoscopy or vaccination