Valéria Silva Santos¹, Fernanda Oliveira do Nascimento¹, Luís Ariel Espinosa Rodríguez ², Fábio César Sousa Nogueira ², Gilberto Barbosa Domont², Felipe Gomes Naveca^1,3, Priscila Ferreira de Aquino¹

Oropouche fever is a neglected arboviruses caused by the Oropouche virus (OROV) and represents a growing challenge to public health in Brazil, with more than 10,000 cases reported in 2025. Although it has clinical and epidemiological relevance, Oropouche fever remains poorly studied compared to other arboviruses, with critical gaps in its pathophysiological understanding. In this context, this study aims to investigate the protein profile of plasma from patients infected with OROV and contribute to the molecular processes of this infection. We analyzed three groups of 10 patients each: OROV+ (Oropouche fever), DENV+ (Dengue) and Control (CAAE: 7.2678.9238.0000.5016). We processed plasma samples following the S-Trap methodology and analyzed by UHPLC coupled to Orbitrap Exploris 480 mass spectrometry, using the Data-Independent Acquisition (DIA) strategy. Protein identification and quantification were performed by DIA-NN software, while statistical and differential expression analyses were conducted using Perseus and MetaboAnalyst 6.0. A total of 495 proteins were identified in the OROV+ group; 490 proteins in the DENV+ group; and 493 proteins in the control group. The Venn Diagram revealed that 413 proteins are common to the three groups. In addition, 428 proteins were shared only between the OROV+ and DENV+ groups. The unique proteins identified for each group, especially those exclusive to OROV+, may be crucial for understanding the specificities of this infection, for example Immunoglobulin IGLV10-54 and IGKV1-12, both related to antibody production. The presence of these molecules only in the OROV+ group suggests a specific immune response against this virus. In addition, we also identified 65 significantly abundant proteins. The Control group presented significantly higher levels of 22 proteins, including coagulation factors (Plasma kallikrein, Factor XI and Fibrinogen chains), components of the complement system (Properdin, Complement factor H-related protein 5) and regulators of inflammation and vascular homeostasis (Apolipoprotein A-IV, Beta-2-glycoprotein 1). The reduction in infected patients suggests mechanisms of viral evasion or inflammatory activation, typical of arboviruses. A marked decrease in fibrinogen chains was also observed in the OROV+ and DENV+, possibly linked to the activation of coagulation and systemic inflammation, which may increase the risk of hemorrhagic complications and serve as a biomarker of severity. However, infected patients showed elevated expression of proteins associated with acute inflammatory processes (C-reactive protein, Serum amyloid A-1, Lipopolysaccharide-binding protein), innate and adaptive immune responses (Complement C9, Complement C4-A, von Willebrand factor, Leukocyte immunoglobulin-like receptor, Beta-2-microglobulin) and regulation of hemostatic and tissue remodeling processes (Thrombospondin-1, Platelet factor 4, Galectin-3-binding protein, SPARC). The observed changes in the coagulation system and inflammatory response may aid in the clinical management of patients, allowing better assessment of the risk of complications. Furthermore, the proteins identified as specific for OROV infection represent promising candidates for future investigations of biomarkers or intervention targets. These results expand the knowledge of the pathophysiological mechanisms of Oropouche fever and open new perspectives for the development of diagnostic and therapeutic strategies.

Agradecimentos: CAPES - Finance Code 001, POSGRAD Program/FAPEAM, ILMD/FIOCRUZ-Amazônia, UFRJ (LADETEC-LABPROT and CPMP).