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Indian Journal of Medical Sciences, Vol. 64, No. 12, December, 2010, pp. 529-531 Editorial Transplacental transmission of influenza virus: What do we know? Andreea A Creanga Epidemic Intelligence Service, Office of Workforce and Career Development, Centers for Disease Control and Prevention, Atlanta, GA; National Center for Chronic Disease Prevention and Health Promotion, Division of Reproductive Health, Correspondence Address: Code Number: ms10001 DOI: 10.4103/0019-5359.76342 Little is known about transplacental transsmission of influenza viruses. Influenza viremia has been reported, [1],[2] but appears to be rare with human influenza. [3] Evidence exists to suggest that the influenza virus can cross the placenta. [1],[4],[5] However, case-reports of transplacental transmission of influenza virus have rarely been described in the clinical literature. This is not surprising given the difficulty in obtaining adequate specimens for documenting infection in placental and fetal tissues. Most recently, Lieberman et al. (2011) published their findings from an investigation of products of conception associated with a 20-week intrauterine fetal demise that occurred after exposure to seasonal (2007/08) influenza A (H1N1) virus early during the pregnancy (weeks 2-6 of gestation). [6] Through immunofluorescence techniques, histiocytes from both the maternal intervillous space and the fetal chorionic villi demonstrated characteristics of viral infection; the absence of immunofluorescence within fetal organs suggested infection of the amniotic fluid and transamnionic passage of the virus. This journal issue includes the 3rd report published to date of possible transplacental transmission of 2009 pandemic influenza A (H1N1) virus (2009 H1N1) to a neonate born to an infected mother. This report illustrates the case of an Indian female neonate delivered by cesarean (under general anesthesia) for fetal distress at 38 completed weeks of gestation; the 22-year old mother developed influenza-like symptoms 8 days before delivery, and required respiratory support for acute respiratory distress from hospital admission (i.e. 2 days before delivery) until 2 weeks postpartum. A throat swab collected from the neonate at 5 hours of life was confirmed positive for 2009 H1N1 by RT-PCR. The neonate developed respiratory distress a few hours after birth, was admitted to the neonatal intensive care unit, and received supplemental oxygen by hood, intravenous fluids, and broad spectrum antibiotics; treatment with oseltamivir was started at birth and continued for 5 days. Two other cases of suspected transplacental transmission of 2009 H1N1 influenza have been reported in the literature. The first report described the case of a newborn delivered at 31 weeks gestation by emergency cesarean section for maternal cardio-pulmonary failure; the mother's influenza symptoms started 7 days before delivery, her clinical course was quite complex, and she died due to respiratory failure 7 days postpartum. [7] A throat swab specimen collected from the neonate at an unspecified time within the first 3 days of life and analyzed by RT-PCR confirmed infection with 2009 H1N1. The second report presented the case of an infant delivered by cesarean for fetal distress at 36 weeks to a 2009 H1N1-infected mother admitted to the hospital with respiratory failure; a nasopharyngeal swab collected from the neonate at 24 hours of life was confirmed positive for 2009 H1N1 by RT-PCR. [8] While possible, the transplacental route of transmission for 2009 H1N1 has not been demonstrated in any of these 3 case-reports. It is true that the 3 infants were delivered by cesarean under general anesthesia to infected and severely ill mothers, and were reportedly "completely isolated" from them upon delivery. However, it is difficult to attribute transmission of influenza to the transplacental route in the absence of documented maternal viremia or of positive immunohistochemical findings from placental and/or fetal tissue examination. Also, transmission of the influenza virus during direct contact with or through respiratory droplets from infected family members or healthcare workers cannot be ruled out in any of these cases. Nonetheless, the 3 case reports and the recently published article by Lieberman et al. [6] raise questions about potential, yet unknown, pathophysiological associations between maternal exposure to influenza, transplacental transmission of the virus and adverse pregnancy outcomes. Clearly, joint epidemiological and immunohistochemical research efforts aimed at answering such questions should include collection and analysis of appropriate tissue specimens. Multiple factors may influence the transplacental passage of influenza and its subsequent effects on the fetus; as proposed by various authors, key among these factors may be the virulence of the influenza strain, [1] the timing of exposure, [6] maternal viremia, [9] maternal immune response, and the use of antiviral agents. [10] Importantly, as Rasmussen et al. (2007) noted, the different degrees of influenza illness severity in the mother and the difficulty in separating the effects of the infection itself from those of the medications used to treat the infection will make research and interpretation of research findings difficult. [10] Yet, such research efforts are greatly needed. References
Copyright 2010 - Indian Journal of Medical Sciences |
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