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Mpox, caused by the monkeypox virus (MPXV), has been associated with adverse pregnancy outcomes, but evidence of vertical transmission remains limited.1–3 Concerns of transplacental transmission are heightened by the ongoing Clade Ib mpox epidemic, which often affects individuals of reproductive age.4 We report three cases of Clade Ib MPXV infection in pregnant women, providing molecular and histopathological evidence of transplacental transmission across all trimesters. (Details of methodology, clinical presentation, and histopathology are in the supplementary appendix.) The first case involved a woman at six weeks of gestation who developed fever, generalized rash, inguinal adenopathy, and genital edema and tested positive for Clade Ib MPXV. Despite symptomatic treatment, she experienced a spontaneous abortion. MPXV DNA was detected in embryonic and placental tissues, with Ct values of 13.4 and 20.1, respectively (Table). Histopathology of these tissues demonstrated MPXV antigen colocalized with CD68 positive placental villous macrophages (Hofbauer cells) and alpha-fetoprotein positive embryonic cells, indicating transplacental transmission (Figure S1A–K).

nic and placental tissues, with Ct values of 13.4 and 20.1, respectively (Table). Histopathology of these tissues demonstrated MPXV antigen colocalized with CD68 positive placental villous macrophages (Hofbauer cells) and alpha-fetoprotein positive embryonic cells, indicating transplacental transmission (Figure S1A–K). The second case involved an HIV-positive woman at 16 weeks of gestation who presented with widespread vesiculopustular lesions, fever, and dysphagia. Fifteen days after she tested positive for Clade Ib MPXV, fetal movements ceased, and ultrasound confirmed intrauterine fetal demise. A cesarean delivery was performed after unsuccessful labor induction; the fetus had several mpox-like lesions on the face, chest, abdomen, and upper limbs. MPXV DNA was detected in placental and fetal tissue, with Ct-values of 19.3 and 18.3, respectively (Table). The third case involved an HIV-positive woman at 34 weeks of gestation with generalized mpox lesions, and genital ulcers, who tested positive for Clade Ib MPXV. She was admitted with hypotension but recovered and was discharged after 29 days. Thirteen days later, at 40 weeks gestation, she delivered a live infant with multiple ulcerative skin lesions (Figure S2); MPXV DNA was detected in placental swab (Ct 23.7) and oropharyngeal swab from the newborn (Ct 38.2). Histopathology revealed MPXV antigen within the placental villi, co-localized with CD68 positive-cells (Figure S1L–P). The mother reported the infant’s death three months later, likely unrelated to mpox.

ns (Figure S2); MPXV DNA was detected in placental swab (Ct 23.7) and oropharyngeal swab from the newborn (Ct 38.2). Histopathology revealed MPXV antigen within the placental villi, co-localized with CD68 positive-cells (Figure S1L–P). The mother reported the infant’s death three months later, likely unrelated to mpox. These findings provide evidence that Clade Ib MPXV can be vertically transmitted, resulting in pregnancy loss or congenital infection, consistent with isolated previous reports on Clade Ia MPXV.1,2 These findings support the need for preventive interventions in pregnant women, including vaccination. Prospective large scale studies are required to better understand perinatal outcomes associated with mpox in pregnancy and to guide clinical management.