Viral, Clinical, and Epidemiological Characteristics of Oropouche Fever in Southeastern Brazil.

Background: Oropouche virus (OROV), an arbovirus causing acute febrile illness, was mostly restricted to the Amazon basin until 2023, when a reassortant lineage spread across Latin America. Increasing numbers of cases have subsequently been reported in extra-Amazonian regions of Brazil. However, follow-up and detailed clinical description is limited. This study aimed to describe viral, clinical, and epidemiological characteristics of OROV cases in the Brazilian states of Rio de Janeiro and Minas Gerais. Methods: This longitudinal study enrolled adults with OROV exposure. Clinical and laboratorial data were assessed, and serum, urine, and saliva samples were tested for OROV RNA and sequenced. Results: From December 2024 to May 2025, 55 OROV cases were recruited (median age: 46, 65% female). The novel OROV reassortant was confirmed by RNA sequencing. The acute phase was characterized by headache (87%), malaise (87%), fever (82%), myalgia (75%), and rash (45%). Recurrence of symptoms occurred in one-third of participants, including malaise (53%), fever (41%), arthralgia (41%), and chills (41%), but without resurgence of viral load. Viral RNA in serum and saliva was primarily detected in the first week of disease, and beyond the third week in urine. Conclusions: Cases appeared in clusters and rash was frequently observed. Symptoms returned after 1 week, indicating the importance of patient follow-up. Cases either lived near banana plantations or participated in recreational activities at waterfalls, raising concerns about ecotourism in the Atlantic Forest. Since OROV RNA was detectable in urine for a prolonged period, urine samples may be useful for diagnosis.