Oropouche fever fatalities and vertical transmission in South America: implications of a potential new mode of transmission

<p dir="ltr">Oropouche fever, caused by the Oropouche orthobunyavirus (OROV), represents a significant yet often overlooked public health issue in South and Central America, particularly in northern Brazil. The virus has been reported in Brazil, Bolivia, Colombia, Cuba, and Peru, totalling 9852 cases as of September 6, 2024, with Brazil accounting for over 80.5% (7931) of those cases (Fig. 1). Up to September 7, 2024, the Ministry of Health of Brazil has reported 7931 cases of OROV infection, 3230 of them in the Amazonas state (40.72%), 1710 in Rondonia state (21.56%), and 886 in Bahia (11.17%). Furthermore, OROV belongs to the Simbu serogroup within the genus Orthobunyavirus, the largest genus of RNA viruses with over 170 named viruses across 18 serogroups and 48 species complexes. The Simbu serogroup includes 22 recognised viruses grouped into seven species complexes: Akabane, Manzanilla, Oropouche, Sathuperi, Simbu, Shamonda, and Shuni. Phylogenetic analysis of the S RNA, which encodes the nucleocapsid protein, has identified four major OROV genotypes (I-IV). Genotype I has been reported in Acre, Amazonas, Maranhão, and Pará in Brazil, as well as in French Guiana. Genotype II occurs in Amapá, Brazil. Genotype III is present in Pará, Brazil, and Panama, while Genotype IV exists in Rondônia, Brazil. Genomic reassortment, where related viruses exchange genetic segments, plays a key role in orthobunyavirus biodiversity. Typically, the S and L segments (coding for nucleocapsid protein and RNA polymerase) are inherited together, while the M segment (coding for viral glycoproteins) mutates more easily under selective pressure.</p>