LAUSR

In August 2015, when we first discussed the idea of a special issue on infections and pregnancy with Drs. Vekemans and Chambers (editor-in-chief and deputy editor of Birth Defects Research Part A), our goal was to highlight infectious diseases, both established and emerging, and their effects on the pregnant woman and her fetus. At that time, Zika virus had been identified in Brazil and was rapidly spreading throughout the country (Campos et al., 2015; Zanluca et al., 2015), but the sharp increase in births of infants with microcephaly had not yet been observed (Kleber de Oliveira et al., 2016). Since then, evidence has accumulated to confirm Zika virus as a teratogen (Rasmussen et al., 2016a), and much has been learned about Zika virus and its effects during pregnancy (Oussayef et al., 2017). Although Zika virus has fueled an interest in infections during pregnancy and their potential teratogenicity, the effects of infectious diseases on the pregnant woman and her fetus have long been recognized. In fact, the first exposure recognized to be a teratogen (rubella) was an infectious one (Webster, 1998; Wesselhoeft, 1947), and several well-recognized teratogens, including cytomegalovirus, toxoplasmosis, syphilis, and varicella zoster, among others, are infections (Običan and Scialli, 2011). In recent years, increased emphasis has been placed on the effects of emerging infections on maternal and child health (Jamieson et al., 2004; Jamieson et al., 2005; Rasmussen and Hayes, 2005; Jamieson et al., 2006; Faherty et al., 2017). Emerging infections during pregnancy are of concern for several reasons (Rasmussen and Hayes, 2005): (1) pregnant women might be more susceptible to or more severely affected by emerging infections (Rasmussen et al., 2012); (2) emerging infections during pregnancy might have adverse effects on the fetus (Rasmussen et al., 2007); and (3) prophylaxis or treatment of emerging infections recommended for the general population might not be appropriate for or accepted by pregnant women (Cono et al., 2006). Emerging infections, initially brought to the forefront in 1992 by an Institute of Medicine report (Institute of Medicine, 1992), are defined as “new, reemerging or drug-resistant infections whose incidence in humans has increased within the past 2 decades or whose incidence threatens to increase in the future.” This broad definition has led to many infectious diseases being characterized as emerging, including several that have recently led the news headlines (i.e., West Nile virus, pandemic H1N1 influenza virus, Middle East Respiratory Syndrome Coronavirus [MERS-CoV], Ebola virus, and, most recently, Zika virus) (Petersen and Hayes, 2008; Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team, et al., 2009; Baize et al., 2014; Petersen et al., 2016; Rasmussen et al., 2016b). Understanding the impact of emerging infections on the pregnant woman and her fetus is still in the early stages, and for many pathogens, little is known. In this special issue, we have included articles on both established as well as emerging infections during pregnancy. Several articles aim to update the reader on established infections with adverse effects on the fetus. As reviewed by Ornoy et al. (in this issue), human parvovirus B19, first described as a DNA virus in 1975 (Cossart et al., 1975) became a recognized cause for fetal effects in the late 1980s (Van Elsacker–Niele et al., 1989). Infection during pregnancy does not seem to have a characteristic pattern of birth defects; however, infection in pregnancy can lead to fetal loss, fetal damage, and, in rare cases, brain abnormalities and neurodevelopmental delays. Parvovirus targets the fetal liver, the main site of hematopoiesis in the fetus, and damages fetal erythrocytes, leading to severe fetal anemia, high output cardiac failure, myocarditis, and nonimmune hydrops. Although women are often immune before their childbearing years, the well-established fetal effects of parvovirus B19 infection generate significant concern among women infected during pregnancy. Pregnancy-related listeriosis is another infection with recognized harmful fetal and neonatal effects: infection during pregnancy is known to cause fetal loss and an increased risk of neonatal mortality. As Wadhwa Desai and Smith (in this issue) discuss in their article, the incidence of infection with this food-borne bacteria has declined over time because of better food safety practices but has now plateaued. Also, improved detection methods have resulted in an increasing number of food recalls and potential exposures. Unfortunately, the underlying *Correspondence to: Dana M. Meaney–Delman, 1600 Clifton Road, MS C12, Centers for Disease Control and Prevention (CDC), Atlanta, GA 30333. E-mail: [email protected]