1. HAOD cohort (Cohort of patients with acute hepatitis of unknown origin)  Patients older than 18 years with acute hepatitis of unknown origin (HAOD)  2. OrthoC-Tx cohort (HEV Screening Cohort in Transplant Patients):  Kidney or liver transplant subjects  3. Ortho-CoRIS Cohort (derived from the AIDS Research Network Cohort (CoRIS))  HIV-infected patients being monitored by the Spanish AIDS Research Network (RIS)  4. TrazHE Cohort (Traceability cohort of Hepatitis E infections)  Patients with the presence of antibodies (IgM) against HEV and absence of HEV-RNA  5. Ortho-C-Rodent Collection:  Wild and peri-urban rodents (rats) from different areas of Spain  6. Ortho-C-Domestic Rodent Collection:  Domestic rodents and mustelids under follow-up in veterinary clinics of different Spanish municipalities.  7. Ortho-C-Carnivore Collection:  Wild carnivores that eat rodents collected by the research team since 2020 in 4 autonomous communities (Extremadura, Andalusia, Murcia and Castilla la Mancha)