Entry, egress and vertical transmission of SARS-CoV-2.

The high infectivity and pathogenicity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have caused the COVID-19 outbreak, one of the most devastating pandemics in more than a century. This pandemic has already left a trail of destruction, including enormous loss of life, a global economic slump, and widespread psychological damage. Despite assiduous world-wide endeavors, an effective cure for COVID-19 is still lacking. Surprisingly, infected neonates and children have relatively mild clinical manifestations and a much lower fatality rate than elderly adults. Recent studies have unambiguously demonstrated the vertical transmission of SARS-CoV-2 from infected pregnant women to fetuses, which creates yet another challenge for disease prevention. In this review, we will summarize the molecular mechanism for entry of SARS-CoV-2 into host cells, the basis for the failure of the lungs and other organs in severe acute cases, and the evidence for congenital transmission.

Probable viremia and positive placental swabs for SARS-CoV-2 in a preterm pregnant woman with mild COVID-19.

This study aimed to report a case of mild novel coronavirus disease (COVID-19) in a pregnant woman with probable viremia, as reverse transcription-polymerase chain reaction (RT-PCR) testing of endometrial and placental swabs for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was positive. A 26-year-old multigravida at 35 weeks 2 days of gestation, who had extensive thigh and abdominal cellulitis, tested SARS-CoV-2 positive by RT-PCR performed on samples from the endometrium and maternal side of the placenta. However, other samples (amniotic fluid, fetal side of the placenta, umbilical cord, maternal vagina, and neonatal nasopharynx) tested negative for SARS-CoV-2. This is one of the rare reports of probable SARS-CoV-2 viremia with the presence of SARS-CoV-2 in the endometrium and placenta, but not leading to vertical transmission and neonatal infection. Because knowledge about transplacental transmission and results is very limited, we conclude that more RT-PCR tests on placental and cord blood samples are needed in order to safely make definite conclusions.

Placental Expression of ACE2 and TMPRSS2 in Maternal Severe Acute Respiratory Syndrome Coronavirus 2 Infection: Are Placental Defenses Mediated by Fetal Sex?

BACKGROUND: Expression of angiotensin-converting enzyme 2 (ACE2) and type II transmembrane serine protease (TMPRSS2), host molecules required for viral entry, may underlie sex differences in vulnerability to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We investigated whether placental ACE2 and TMPRSS2 expression vary by fetal sex in the presence of maternal SARS-CoV-2 infection. METHODS: Placental ACE2 and TMPRSS2 expression was quantified by quantitative reverse transcription polymerase chain reaction (RT-PCR) and by Western blot in 68 pregnant women (38 SARS-CoV-2 positive, 30 SARS-CoV-2 negative) delivering at Mass General Brigham from April to June 2020. The impact of fetal sex and maternal SARS-CoV-2 exposure on ACE2 and TMPRSS2 was analyzed by 2-way analysis of variance (ANOVA). RESULTS: Maternal SARS-CoV-2 infection impacted placental TMPRSS2 expression in a sexually dimorphic fashion (2-way ANOVA interaction, P = .002). We observed no impact of fetal sex or maternal SARS-CoV-2 status on ACE2. TMPRSS2 expression was significantly correlated with ACE2 expression in males (Spearman ρ = 0.54, P = .02) but not females (ρ = 0.23, P = .34) exposed to maternal SARS-CoV-2. CONCLUSIONS: Sex differences in placental TMPRSS2 but not ACE2 were observed in the setting of maternal SARS-CoV-2 infection, which may have implications for offspring vulnerability to placental infection.

Placental Immune Responses to Viruses: Molecular and Histo-Pathologic Perspectives.

As most recently demonstrated by the SARS-CoV-2 pandemic, congenital and perinatal infections are of significant concern to the pregnant population as compared to the general population. These outcomes can range from no apparent impact all the way to spontaneous abortion or fetal infection with long term developmental consequences. While some pathogens have developed mechanisms to cross the placenta and directly infect the fetus, other pathogens lead to an upregulation in maternal or placental inflammation that can indirectly cause harm. The placenta is a temporary, yet critical organ that serves multiple important functions during gestation including facilitation of fetal nutrition, oxygenation, and prevention of fetal infection in utero. Here, we review trophoblast cell immunology and the molecular mechanisms utilized to protect the fetus from infection. Lastly, we discuss consequences in the placenta when these protections fail and the histopathologic result following infection.

COVID-19 in pregnancy: What we know from the first year of the pandemic.

The COVID-19 pandemic has infected nearly 178 million people and claimed the lives of over 3.8 million in less than 15 months. This has prompted a flurry of research studies into the mechanisms and effects of SARS-CoV-2 viral infection in humans. However, studies examining the effects of COVID-19 in pregnant women, their placentae and their babies remain limited. Furthermore, reports of safety and efficacy of vaccines for SARS-CoV-2 in pregnancy are limited. This review concisely summarises the case studies and research on COVID-19 in pregnancy, to date. It also reviews the mechanism of infection with SARS-CoV-2, and its reliance and effects upon the renin-angiotensin-aldosterone system. Overall, the data suggest that infection during pregnancy can be dangerous at any time, but this risk to both the mother and fetus, as well as placental damage, increases during the third trimester. The possibility of vertical transmission, which is explored in this review, remains contentious. However, maternal infection with SARS-CoV-2 can increase risk of miscarriage, preterm birth and stillbirth, which is likely due to damage to the placenta.

Significance of the placental barrier in antenatal viral infections.

The placenta provides a significant physical and physiological barrier to prevent fetal infection during pregnancy. Nevertheless, it is at times breached by pathogens and leads to vertical transmission of infection from mother to fetus. This review will focus specifically on the Zika flavivirus, the HIV retrovirus and the emerging SARS-CoV2 coronavirus, which have affected pregnant women and their offspring in recent epidemics. In particular, we will address how viral infections affect the immune response at the maternal-fetal interface and how the placental barrier is physically breached and discuss the consequences of infection on various aspects of placental function to support fetal growth and development. Improved understanding of how the placenta responds to viral infections will lay the foundation for developing therapeutics to these and emergent viruses, to minimise the harms of infection to the offspring.

Term Human Placental Trophoblasts Express SARS-CoV-2 Entry Factors ACE2, TMPRSS2, and Furin.

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has had a massive impact on human lives worldwide. While the airborne SARS-CoV-2 primarily affects the lungs, viremia is not uncommon. As placental trophoblasts are directly bathed in maternal blood, they are vulnerable to SARS-CoV-2. Intriguingly, the human fetus is largely spared from SARS-CoV-2 infection. We tested whether the human placenta expresses the main SARS-CoV-2 entry factors angiotensin-converting enzyme 2 (ACE2), transmembrane protease serine 2 (TMPRSS2), and furin and showed that ACE2 and TMPRSS2 are expressed in the trophoblast rather than in other placental villous cells. While furin is expressed in the main placental villous cell types, we surveyed, trophoblasts exhibit the highest expression. In line with the expression of these entry factors, we demonstrated that a SARS-CoV-2 pseudovirus could enter primary human trophoblasts. Mechanisms underlying placental defense against SARS-CoV-2 infection likely involve postentry processing, which may be germane for mitigating interventions against SARS-CoV-2.IMPORTANCE Pregnant women worldwide have been affected by COVID-19. As the virus is commonly spread to various organs via the bloodstream and because human placental trophoblasts are directly bathed in maternal blood, feto-placental infection by SARS-CoV-2 seems likely. However, despite the heightened risk to pregnant women, thus far the transmission risk of COVID-19 to the feto-placental unit seems extremely low. This has been recently attributed to a negligible expression of SARS-CoV-2 entry factors in the human placenta. We therefore sought to explore the expression of the entry factors ACE2 and TMPRSS2 in the different cell types of human placental villi. Using a combination of transcriptome sequencing (RNA-seq), real-time quantitative PCR (RT-qPCR), in situ hybridization, and immunofluorescence, we found that trophoblasts, but not the other main villous cell types, express ACE2 and TMPRSS2, with a broad expression of furin. Correspondingly, we also showed that primary human trophoblasts are permissive to entry of SARS-CoV-2 pseudovirus particles.

Fetal and placental infection with SARS-CoV-2 in early pregnancy.

To date, mother-to-fetus transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for the coronavirus disease 2019 (COVID-19) pandemic, remains controversial. Although placental COVID-19 infection has been documented in some cases during the second- and third-trimesters, no reports are available for the first trimester of pregnancy, and no SARS-CoV-2 protein has been found in fetal tissues. We studied the placenta and fetal organs from an early pregnancy miscarriage in a COVID-19 maternal infection by immunohistochemical, reverse transcription quantitative real-time polymerase chain reaction, immunofluorescence, and electron microscopy methods. SARS-CoV-2 nucleocapsid protein, viral RNA, and particles consistent with coronavirus were found in the placenta and fetal tissues, accompanied by RNA replication revealed by double-stranded RNA (dsRNA) positive immunostain. Prominent damage of the placenta and fetal organs were associated with a hyperinflammatory process identified by histological examination and immunohistochemistry. The findings provided in this study document that congenital SARS-CoV-2 infection is possible during the first trimester of pregnancy and that fetal organs, such as lung and kidney, are targets for coronavirus. The infection and multi-organic fetal inflammation produced by SARS-CoV-2 during early pregnancy should alert clinicians in the assessment and management of pregnant women for possible fetal consequences and adverse perinatal outcomes.

Investigating the risk of maternal-fetal transmission of SARS-CoV-2 in early pregnancy.

INTRODUCTION: The possibility of vertical transmission of SARS-CoV-2 from the mother to the fetus is one of the most crucial issues regarding the COVID-19 effects on pregnancy. In this study, we aimed to explore the risk of maternal-fetal transmission before 24 weeks of gestation, through analysis of abortion materials collected from PCR-positive women with pregnancy loss. To the best of our knowledge, apart from case reports, this study is the first prospective work on the vertical transmission of SARS-CoV-2 in early pregnancy. METHODS: The patients who had attended our clinic with the diagnosis of pregnancy loss before 24 weeks of gestation were screened for COVID-19. Vertical transmission in PCR-positive women was assessed through the presence of SARS-CoV-2 RNA in fetal-placental tissues by rt-PCR test. RESULTS: 24 of 210 (%11,4) pregnant women participating in the study had positive rt-PCR results. Placenta and curettage material samples of these PCR-positive patients were analyzed and all valid test results (21 samples) were negative for SARS CoV-2 RNA. In three cases, the rt-PCR results were invalid due to failed internal controls. DISCUSSION: In the literature, the possibility of intrauterine vertical transmission of SARS-CoV-2 is still controversial. The findings of the present study did not reveal any evidence of vertical transmission of SARS-CoV-2 in early pregnancy.

Single-cell RNA expression profiling of SARS-CoV-2-related ACE2 and TMPRSS2 in human trophectoderm and placenta.

OBJECTIVES: To examine the characteristics and distribution of possible severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) target cells in the human trophectoderm (TE) and placenta. METHODS: Bioinformatics analysis was performed based on published single-cell transcriptomic datasets of early TE and first- and second-trimester human placentae. We conducted the transcriptomic analysis of 4198 early TE cells, 1260 first-trimester placental cells and 189 extravillous trophoblast cells (EVTs) from 24-week placentae (EVT_24W) using the SMART-Seq2 method. In addition, to confirm the bioinformatic results, we performed immunohistochemical staining of three first-trimester, three second-trimester and three third-trimester placentae from nine women recruited prospectively to this study. We evaluated the expression of the SARS-CoV-2-related molecules angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2). RESULTS: Via bioinformatic analysis, we identified the existence of ACE2 and TMPRSS2 expression in human TE as well as in first- and second-trimester placentae. In the human TE, 54.4% of TE1 cells, 9.0% of cytotrophoblasts (CTBs), 3.2% of EVTs and 29.5% of syncytiotrophoblasts (STBs) were ACE2-positive. In addition, 90.7% of TE1 cells, 31.5% of CTBs, 22.1% of EVTs and 70.8% of STBs were TMPRSS2-positive. In placental cells, 20.4% of CTBs, 44.1% of STBs, 3.4% of EVTs from 8-week placentae (EVT_8W) and 63% of EVT_24W were ACE2-positive, while 1.6% of CTBs, 26.5% of STBs, 1.9% of EVT_8W and 20.1% of EVT_24W were TMPRSS2-positive. Pathway analysis revealed that EVT_24W cells that were positive for both ACE2 and TMPRSS2 (ACE2 + TMPRSS2-positive) were associated with morphogenesis of branching structure, extracellular matrix interaction, oxygen binding and antioxidant activity. The ACE2 + TMPRSS2-positive TE1 cells were correlated with an increased capacity for viral invasion, epithelial-cell proliferation and cell adhesion. Expression of ACE2 and TMPRSS2 was observed on immunohistochemical staining in first-, second- and third-trimester placentae. CONCLUSIONS: ACE2- and TMPRSS2-positive cells are present in the human TE and placenta in all three trimesters of pregnancy, which indicates the possibility that SARS-CoV-2 could spread via the placenta and cause intrauterine fetal infection. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Intrauterine Transmission of SARS-CoV-2.

We documented fetal death associated with intrauterine transmission of severe acute respiratory syndrome coronavirus 2. We found chronic histiocytic intervillositis, maternal and fetal vascular malperfusion, microglial hyperplasia, and lymphocytic infiltrate in muscle in the placenta and fetal tissue. Placenta and umbilical cord blood tested positive for the virus by PCR, confirming transplacental transmission.

Description of a late miscarriage case at 16 Weeks of Gestation associated with a SARS-CoV-2 infection.

BACKGROUND: Data about obstetric complications of maternal infection by SARS-CoV-2 remain sparse. CASE: A 40-year-old pregnant woman, gravida 3 para 1 with no previous obstetric complications, presented a late miscarriage at 16 weeks of gestation on day 9 of COVID-19 disease. The results of her nasopharyngeal swab for SARS-CoV-2, tested the same day, were negative, but the placenta was infected by SARS-CoV-2 and serology was positive 11 days later. No other obstetric or infectious cause was found to explain this outcome. CONCLUSION: This case strongly suggests that SARS-CoV-2 may lead to a late miscarriage.

Congenital, Intrapartum and Postnatal Maternal-Fetal-Neonatal SARS-CoV-2 Infections: A Narrative Review.

BACKGROUND: There is inconclusive evidence regarding congenital, intrapartum, and postnatal maternal-fetal-neonatal SARS-CoV-2 infections during the COVID-19 pandemic. A narrative review was conducted with the aim of guiding clinicians on the management of pregnant women with respect to congenital, intrapartum, and postnatal maternal-fetal-neonatal SARS-CoV-2 infections and breastfeeding during the COVID-19 pandemic. METHODS: Searches were conducted in Web of Science, PubMed, Scopus, Dialnet, CUIDEN, Scielo, and Virtual Health Library to identify observational, case series, case reports, and randomized controlled trial studies assessing the transmission of SARS-CoV-2 from mother to baby and/or through breastfeeding during the COVID-19 pandemic. RESULTS: A total of 49 studies was included in this review, comprising 329 pregnant women and 331 neonates (two pregnant women delivered twins). The studies were performed in China (n = 26), USA (n = 7), Italy (n = 3), Iran (n = 2), Switzerland (n = 1), Spain (n = 1), Turkey (n = 1), Australia (n = 1), India (n = 1), Germany (n = 1), France (n = 1), Canada (n = 1), Honduras (n = 1), Brazil (n = 1), and Peru (n = 1). Samples from amniotic fluid, umbilical cord blood, placenta, cervical secretion, and breastmilk were collected and analyzed. A total of 15 placental swabs gave positive results for SARS-CoV-2 ribonucleic acid (RNA) on the fetal side of the placenta. SARS-CoV-2 RNA was found in seven breastmilk samples. One umbilical cord sample was positive for SARS-CoV-2. One amniotic fluid sample tested positive for SARS-CoV-2. CONCLUSIONS: This study presents some evidence to support the potential of congenital, intrapartum, and postnatal maternal-fetal-neonatal SARS-CoV-2 infections during the COVID-19 pandemic. Mothers should follow recommendations including wearing a facemask and hand washing before and after breastfeeding.

Changes in physiology and immune system during pregnancy and coronavirus infection: A review.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the 3rd epidemic coronavirus after severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV). Since December 2019, the outbreak of the Coronavirus Disease 2019 (COVID-19) caused by SARS-CoV-2 has aroused great attention around the world. Pregnant women and their fetuses have been concerned as a high-risk population. We explained why pregnant women are susceptible to coronavirus in terms of their adaptive changes in physiology and immune system during pregnancy, and described the associations between maternal clinical symptoms, perinatal outcomes and coronavirus infections.

Potential effects of SARS-CoV-2 infection during pregnancy on fetuses and newborns are worthy of attention.

The outbreak of the 2019 novel coronavirus disease (SARS-CoV-2) has resulted in a major epidemic threat worldwide. However, the effects of neoviruses on infected pregnant women and especially on their fetuses and newborns are not well understood. Most up-to-date evidences about how SARS-CoV-2 affected patients especially in pregnancy were collected by conducting a comprehensive search of medical literature electronic databases. Immune-related data of pregnant women, fetuses and newborns were further analysis. According to the limited literature, SARS-CoV-2 utilizes angiotensin converting enzyme 2 as its receptor and causes severe hypoxemia. Insufficiency of angiotensin converting enzyme 2 in pregnant women and the effects of hypoxia on the placental oxygen supply will cause severe perinatal complications. In addition, SARS-CoV-2 infection may disrupt maternal-fetal immune tolerance and cause immunological damage to embryos. Because of these reasons, pregnancy complications such as fetal demise or premature birth, preeclampsia, intrauterine growth restriction, respiratory dyspnea, nervous system dysplasia and immune system defects are likely to occur in pregnant women with COVID-19 or their newborns. Pregnant women infected with SARS-CoV-2 should be treated as a special group and given special attention. Fetuses and newborns of SARS-CoV-2-infected pregnant women should be given more protection to reduce the occurrence of adverse events. In this review, we intend to provide an overview of the physiological and immunological changes that induce the pregnancy complications. This article will benefit the treatment and prognosis of fetuses and newborns of SARS-CoV-2-infected pregnant women.

Effects of altered photoperiod due to COVID-19 lockdown on pregnant women and their fetuses.

Maternal circadian rhythms provide highly important input into the entrainment and programming of fetal and newborn circadian rhythms. The light-dark cycle is an important regulator of the internal biological clock. Even though pregnant women spend a greater part of the day at home during the latter stages of pregnancy, natural light exposure is crucial for the fetus. The current recommended COVID-19 lockdown might dramatically alter normal environmental lighting conditions of pregnant women, resulting in exposure to extremely low levels of natural daylight and high-intensity artificial light sources during both day and night. This article summarizes the potential effects on pregnant woman and their fetuses due to prolonged exposure to altered photoperiod and as consequence altered circadian system, known as chronodisruption, that may result from the COVID-19 lockdown.

Hypothesized behavioral host manipulation by SARS-CoV2/COVID-19 infection.

Although not widely studied, behavioral host manipulation by various pathogens has been documented. Host manipulation is the process by which a pathogen evolves adaptations to manipulate the behavior of the host to maximize reproduction (Ro) of the pathogen. The most notable example is rabies. When a host is infected with the rabies virus it gets into the host's central nervous system and triggers hyper aggression. The virus is also present in the rabid animal's saliva so being bitten transmits the infection to a new host and the old host is left to eventually die if untreated. Toxoplasmosis is another example. When mice are infected they demonstrate a fearlessness toward cats, thus increasing their chances of being eaten. Toxoplasmosis needs the digestive tract of the feline to survive. Recent studies have shown that exposure to toxoplasmosis in humans (e.g., through cat feces) has also been associated with behavioral changes that are predicted to enhance the spread of the pathogen. Even the common influenza virus has been shown to selectively increase in-person sociality during the 48-hour incubation period, thus producing an obvious vector for transmission. Here we hypothesize that the novel coronavirus, SARS-CoV2, which produces the COVID-19 disease may produce similar host manipulations that maximize its transmission between humans.