Summary
Background
Although adverse maternal and infant outcomes have been reported following Oropouche virus infection, the frequencies of these outcomes have not been compared with those in uninfected pregnancies. We followed up pregnant women from areas with Oropouche virus transmission in Rio de Janeiro state, Brazil, to evaluate potential adverse maternal and infant outcomes following Oropouche virus exposure.
Methods
In this prospective cohort study across the state of Rio de Janeiro, Brazil, we included pregnant women receiving prenatal care in municipalities with or at high risk of Oropouche virus outbreaks. Inclusion criteria were: ongoing risk of Oropouche virus infection at the time of prenatal visit; prenatal care at one of the participating sites; and willingness and ability to consent to and participate in the study. Exclusion criteria included infection with other arboviruses and fetal chromosomal abnormalities. Maternal blood, urine, and saliva were collected and tested for Oropouche virus by RT-PCR at enrolment and pregnancy endpoints. IgG and IgM serologies from maternal blood, placental tissue PCR, and immunohistochemistry were done. Confirmed infections were defined by: positive Oropouche virus PCR in blood, urine, saliva, or placenta; positive Oropouche virus placental immunohistochemistry; or Oropouche virus-specific IgM or IgG seroconversion. Possible infection was defined as one positive IgM result without a positive PCR. Negative results ruled out infection. Adverse maternal outcomes (reported by study investigators following up participants at study sites) were maternal death or disability, fetal loss, or haemorrhage; adverse infant outcomes were neonatal death or malformations. Relative risks adjusted for maternal age, other congenital infections, and use of tobacco, alcohol, and drugs during pregnancy for adverse maternal and infant outcomes were calculated.
Findings
Between Nov 29, 2024, and Oct 8, 2025, 544 participants were enrolled: 130 (24%) with confirmed, 143 (26%) with possible, and 271 (50%) with no Oropouche virus infection. The median cycle threshold value of RT-PCR was 29·7 (IQR 25·8–34·9). Among the 130 women with confirmed infection, 104 (80%) developed detectable IgG antibodies. Symptoms were present in 80 (62%) women with confirmed infection, not necessarily associated with adverse outcomes (adjusted relative risk [aRR] 0∙84 [95% credible interval 0∙51–1∙21]). By the end of follow-up, the pregnancies of 119 women with confirmed infection and 193 with no infection had resulted in livebirth, stillbirth, or miscarriage; 105 (88%) women with confirmed infection had livebirths and 187 (97%) women without infection had livebirths. Adverse maternal outcomes occurred in 21 (18%) women with confirmed infection and 14 (7%) women with no infection (aRR 2∙90 [1∙52–5∙35]). Fetal loss and haemorrhage risk were three times higher in women with confirmed infection than in those with no infection (aRR 3∙08 [1∙28–7∙29] for fetal loss and 2∙79 [1∙22–6∙21] for haemorrhage). The aRR for adverse infant outcomes was 9∙18 (1∙89–47∙88). CNS abnormalities occurred in eight (8%) infants of mothers with confirmed infection and in no infants of mothers with no infection.
Interpretation
Oropouche virus infection during pregnancy is associated with severe maternal and infant outcomes, including maternal haemorrhage, fetal loss, and infant CNS abnormalities.
Funding
The Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ), the National Council for Scientific and Technological Development (CNPq), the Brazilian Ministry of Health, the Oswaldo Cruz Foundation (Fiocruz), and the European Health and Digital Executive Agency.
Translation
For the Portuguese translation of the abstract see Supplementary Materials section.
Source:
Link: https://doi.org/10.1016/S1473-3099(26)00493-7
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