Oropouche fever epidemic in Northern Brazil: epidemiology and molecular characterization of isolates.

Background: Oropouche fever virus is an important arbovirus associated with febrile disease that reemerged in 2006 in several municipalities of Para State, Bragantina region, Amazon, Brazil, 26 years after the last epidemic. Objective: To investigate an Oropouche fever outbreak in this region. Study design: A serologic survey and prospective study of acute febrile cases were performed in Magalhaes Barata (urban and rural areas) and Maracana (rural area) municipalities. Serology (IgM-ELISA and hemagglutination-inhibition [HI]), virus isolation, RT-PCR and real-time-PCR were used to confirm Oropouche virus (OROV) as responsible for the febrile outbreaks. Results: Real-time-PCR showed high titers of OROV in acute-phase serum samples from febrile patients. From 113 of 119 acutely febrile patients with paired serum samples, OROV infections was confirmed by serologic conversion (n = 76) or high titers (n = 37) for both HI and IgM-ELISA. Patients had a febrile disease characterized by headache, chills, dizziness, photophobia, myalgia, nausea, and vomiting. Females and children under 15 years of age were most affected. Nucleotide sequencing of six OROV isolates identified that genotype II was associated with the human disease epidemic. Conclusions: Oropouche fever, which has re-emerged in the Bragantina region in eastern Amazon 26 years after the last epidemic, is caused by genotype II, a lineage previously found only in Peru and western Brazil. © 2008 Elsevier B.V. All rights reserved.