Mast Cell Treatment in Post-tick Bite Illness (PTBI)

Inclusion Criteria: * In order to be eligible to participate in this study, an individual must meet all of the following criteria: * Ability to understand and provide informed consent in English (a translator will not be present during screening, consent or follow-up visits) * Age 21-65 years old and of any gender, race, and ethnicity at the time of the initial visit. * History of Ehrlichiosis and/or Rocky Mountain Spotted Fever (RMSF) within the last 36 months diagnosed and treated by a healthcare provider more than 6 months previously with current symptoms causing clinically significant distress or impairment in functioning as measured by a mast cell symptom scale score \>88 ± 9 * OR - History of alpha-gal syndrome (AGS) with an alpha-gal Immunoglobulin E (IgE) \>0.1 IU/mL and managed on an appropriate avoidance diet for more than 6 months previously with current symptoms causing clinically significant distress or impairment in functioning as measured by a mast cell symptom scale score \>88 ± 9 * Females of childbearing potential must have a negative pregnancy test prior to study entry * Ability to refrain from diphenhydramine ("Benadryl") during the study period Exclusion Criteria: * Any individual who meets one or more of the following criteria will be excluded from participation: * History of allergy, intolerance or hypersensitivity to fexofenadine, cromolyn or ketotifen (as documented by self-report and/or medical chart review) * History of a prior c…