Oropouche Fever Outbreak, Manaus, Brazil, 2007–2008

induced protection from egg production losses in commercial turkey breeder hens following experimental challenge with a triple-reassortant H3N2 avian infl uenza virus.opment of a real-time reverse transcriptase PCR assay for type A infl uenza virus and the avian H5 and H7 hemagglutinin sub-types. Limited susceptibility and lack of systemic infection by an H3N2 swine infl uenza virus in intrana-sally inoculated chickens. YM. Interspecies and intraspecies transmission of triple reassortant H3N2 infl u-enza A viruses. To the Editor: Oropouche virus (OROV) is an arbovirus, Orthobu-nyavirus, transmitted among sloths, marsupials, primates, and birds by the mosquitoes Aedes serratus and Culex quinquefasciatus. Notably, this virus has adapted to an urban cycle involving man, with midges (Culicoides paraen-sis) as the main vector (1). Oropouche fever is the second most frequent ar-boviral disease in Brazil, surpassed only by dengue. OROV causes large, explosive outbreaks of acute febrile illness in cities and villages in the Amazon and central regions of Brazil. An estimated 500,000 cases of OROV infection have occurred in Brazil in the past 48 years. In addition to outbreaks, OROV can also cause sporadic human infections (2). The Tropical Medicine Foundation of Amazonas State (TMF-AM) is a tertiary care center specializing in tropical and infectious diseases and is located in the city of Manaus. Syn-dromic surveillance for acute febrile illness has been conducted by TMF-AM since 1998. During January 2007 through November 2008, we obtained blood samples from 631 patients who had acute febrile illness for ≥5 days but who had negative results at initial screening for malaria (thick blood smear) and dengue (MAC-ELISA). Blood samples were tested for OROV immunoglobulin (Ig) M antibodies by an indirect enzyme immune assay using infected cells as antigen, as previously reported for dengue (3). For the indirect enzyme immune assay using infected cells as antigen, C6/36 A. albopictus cells were grown in 96 well microplates; these cells were infected with OROV (BeAn 1991 strain). After 4 days, the cells were fi xed in the wells with 7% formalin buffered at pH 7.0. The microplate was blocked with 5% skim milk and, after washing the wells, 100 μL of serum diluted 1:400 was added into infected and uninfected wells. After incubation and washing the wells, a peroxidase-conjugated goat anti-human IgM was added; fi nally, the ABTS substrate was added into the wells. The plates were incubated and read on a spec-trophotometer at 405 nm. The cutoff for the …