Patient description: A 53-year-old man presents with chronic HCV infection for the past 2 years. His past medical history is only significant for inguinal hernia surgery when he was 20 years old. He is on IFN (100 mg/week) plus RBV (400 mg/day) combination therapy for the past 9 months. Direct antiviral drugs were added to his treatment 6 months ago. His medical record shows previous positive HCV RNA tests as well as positive enzyme immunoassay for anti-HCV-antibodies. The recent biopsy was negative for hepatocellular carcinoma and was only remarkable for chronic inflammation compatible with a chronic viral hepatitis. There is no evidence of alcoholic liver disease, bleeding from esophageal varices, hemochromatosis, autoimmune hepatitis or metabolic liver disease. He is an alert male with no acute distress. His BP: 130/75, HR: 90/min and BMI: 27. His abdomen is soft with no ascites or tenderness. The lower extremities are normal with no edema.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Hepatitis E Hepatitis Chronic Viral Willing and able to provide written informed consent 2. Male or female, age ≥ 18 years 3. Confirmation of chronic HEV infection documented by: Positive HEV RNA at least 3 months before Screening, and positive for HEV RNA at the time of Screening 4. Documented previous ribavirin therapy or documented contraindication for full dose (≥ 600mg qd) ribavirin monotherapy for at least 3 months 5. Body mass index (BMI) ≥ 18 kg/m2 6. Screening ECG without clinically significant abnormalities 7. Subjects must have the following laboratory parameters at screening Platelets ≥ 60,000/μL INR ≤2.0 x ULN unless subject has known hemophilia or is stable on an anticoagulant regimen affecting INR HbA1c ≤ 10% Creatinine clearance (CLcr) ≥ 30 mL/min, as calculated by the Cockcroft-Gault equation (using actual body weight) 8. Subject has not been treated with any investigational drug or device within 42 days of the Screening visit 9. A negative serum pregnancy test is required for female subjects (unless surgically sterile or women ≥ 54 years of age with cessation for 24 ≥ months of previously occurring menses). Complete abstinence from intercourse. Periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods) is not permitted. Or Consistent and correct use of 1 of the following methods of birth control listed below, in addition to a male partner who correctly uses a condom, from the date of Screening until 30 days after last dose of study drug intrauterine device (IUD) with a failure rate of < 1% per year female barrier method: cervical cap or diaphragm with spermicidal agent tubal sterilization vasectomy in male partner hormone-containing contraceptive  Clinically-significant illness (other than HEV) or any other major medical disorder that, in the opinion of the investigator, may interfere with subject treatment, assessment or compliance with the protocol. 2. Ribavirin administration within the last 28 days. 3. Infection with the hepatitis C virus (defined as HCV RNA positive) 4. Gastrointestinal disorder or post-operative condition that could interfere with the absorption of the study drug (for example, gastric bypass or severe ulcerative colitis). 5. Difficulty with blood collection and/or poor venous access for the purposes of phlebotomy. 6. Psychiatric hospitalization, suicide attempt, and/or a period of disability as a result of their psychiatric illness within the last 2 years. Subjects with psychiatric illness that is wellcontrolled on a stable treatment regimen for at least 12 months prior to screening or has not required medication in the last 12 months may be included. 7. Significant drug allergy (such as anaphylaxis or hepatotoxicity). 8. Pregnant or nursing female 9. Clinically-relevant drug or alcohol abuse within 12 months of screening including any uncontrolled drug use within 6 months of screening. A positive drug screen will subjects unless it can be explained by a prescribed medication; the diagnosis and prescription must be approved by the investigator. Uncontrolled users of intravenous drugs will not be permitted to enroll in the study. 10. Use of any prohibited concomitant medications within 21 days of the Baseline/Day 1 visit. Use of Amiodaron as concomitant medication is prohibited within 60 days of Baseline/Day1 visit. 11. Known hypersensitivity to SOF or formulation excipients