Call 001/2013 - PPSUS / 062.00656/2014 and call 001/2014 - PROEP / 062.01939/2014Fundação de Amparo à Pesquisa do Estado do Amazonas - FAPEAMIntroduction: Several orthobunyaviruses are important arthropod-borne pathogens, responsible for a variety of diseases in humans, from acute febrile illness to encephalitis. Methods: We collected serum samples from a series of dengue suspected cases in Tefé, a mid-size city located in the interior of the Amazonas state, Brazil. Viral RNA extraction was performed, and specimens were tested for dengue virus using RT-PCR. Thirty dengue negative samples were further tested for Mayaro virus (MAYV) and Oropouche virus (OROV) using an RT-qPCR protocol previously described. Positive samples were characterized by MegaBLAST analysis over the entire nucleotide collection of the main public databases, and also by maximum likelihood phylogenetic reconstruction of the S genome segment. Results: We detected nine OROV or OROV-like positive cases among 30 patients reporting fever and headache, as the most common symptoms. The closest nucleotide sequence returned from the MegaBLAST analysis belongs to an OROV isolated in Peru 2008. Moreover, all Tefé samples grouped in the same clade with the OROV reference sequence and other closely-related OROV-like viruses. Discussion: Dengue viruses are still the most important arbovirus worldwide, causing hundreds of millions of infections every year. Nonetheless, other arboviruses like chikungunya virus, Zika virus, and yellow fever virus have emerged in the last few years and are now a public health concern in several countries. OROV is believed to have caused more than 500,000 febrile infections in Brazil over recent decades. Therefore, the results described in this study strengthen that this arbovirus, and its closely-related recombinants, should be under continuous surveillance, at least in the endemic countries of Latin America.