Oropouche virus in pregnancy: fetal loss, haemorrhage and infant CNS abnormalities

Design

Prospective cohort

Population

544 pregnant women in Oropouche-affected areas of Rio de Janeiro state

Primary outcome

Adverse maternal and infant outcomes by infection status

Effect

Maternal adverse outcomes 18% vs 7% (aRR 2.90, 1.52–5.35); infant aRR 9.18 (1.89–47.88)

A prospective cohort in The Lancet Infectious Diseases enrolled 544 pregnant women receiving antenatal care in parts of Rio de Janeiro state with or at high risk of Oropouche outbreaks, testing blood, urine, saliva and placenta by PCR and serology. 130 had confirmed infection, 143 possible infection and 271 none.

Adverse maternal outcomes — death, disability, fetal loss or haemorrhage — occurred in 18% of confirmed infections and 7% of uninfected women (aRR 2.90). Fetal loss (aRR 3.08) and haemorrhage (aRR 2.79) were about three times as likely. CNS abnormalities occurred in 8% of infants of infected mothers and none of the others. Only 62% of confirmed infections caused symptoms, and symptoms did not predict who had a poor outcome.

Oropouche has spread across Latin America and the Caribbean since 2024, and earlier reports of vertical transmission were case series. This is the first cohort to compare outcomes with uninfected pregnancies, and it suggests the risk is real and substantial.

The practical concern for clinicians outside the region is travel. Ask pregnant women about travel to affected areas, and consider Oropouche alongside dengue, Zika and chikungunya when a pregnant traveller has a febrile illness.

• Ask pregnant women about recent travel to Oropouche-affected areas in Latin America and the Caribbean
• Consider Oropouche testing alongside dengue, Zika and chikungunya in a febrile pregnant traveller
• Do not rule out infection because the woman had no symptoms; over a third were asymptomatic
• Advise pregnant women planning travel to affected areas about insect bite prevention
• Arrange detailed fetal imaging after confirmed infection in pregnancy

Why it matters

Oropouche now joins Zika on the list of arboviruses that harm pregnancies.

Don't overread it

This was observational, with wide intervals for infant outcomes; the size of the infant risk is uncertain.

The statistics, in plain English

The infant outcome aRR of 9.18 has a credible interval from 1.89 to 47.88: the risk is clearly raised, but the data cannot say by how much. The maternal estimate (2.90, 1.52–5.35) is more precise.

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