Lisa Nowoslawski Akhtar

Neonatal herpes simplex virus disease most often occurs following mother-to-neonate transmission during childbirth. However, genomic differences between the maternal and neonatal viral populations are poorly understood. Here, we performed deep whole-genome sequencing of clinical HSV-2 samples obtained from a maternal-neonatal dyad to investigate viral population dynamics during transmission.

Background: Herpes simplex virus (HSV) type 1 and 2 infect over 14,000 newborns each year globally, with most cases (55%) causing a severe outcome that can be fatal if untreated. Neonatal disease severity and long-term outcomes remain unpredictable, and elucidating viral factors that contribute to these outcomes remains a challenge. However, through viral genomic and phenotypic analysis of HSV isolated from neonatal patients, we can begin to connect aspects of viral diversity with clinical patient data. Methods: Here we have applied viral whole genome sequencing to a collection of residual clinical diagnostic samples from ten neonates who had either mild or severe HSV-1 infections. Samples from different body sites or across recurrences allowed for both within- and between-host comparisons. From 30 residual diagnostic samples, we successfully isolated 14 viral cultures. These cultured viruses enabled additional phenotypic analyses, including in vitro growth evaluation in multiple cell types and an in vivo murine model of infection. Results: These data highlight the diversity found in HSV-1 isolated from neonates. Through comparative genomics approaches, we demonstrate both within- and between-host diversity of these samples. Growth of cultured isolates in cell-based assays and a murine model of infection reveal additional aspects of within- and between-host differences. Conclusions: Overall, this study presents the first investigation into the viral diversity of neonatal HSV-1, which is now more common in the US than neonatal HSV-2. Through integration of phenotypic, genomic, and clinical data we characterized these neonatal viral samples to begin unraveling the complexity of neonatal HSV-1 infections.

The use of multiplex polymerase chain reaction (PCR) panels for diagnosis of clinical syndromes is rapidly growing despite limited data on optimal use cases. We retrospectively reviewed the clinical impact and consequences of the inclusion of herpesvirus targets on the meningitis/encephalitis PCR panel.

The ability of herpes simplex virus (HSV) to establish lifelong latency in sensory neurons makes it one of the most pervasive viruses worldwide. Although most HSV infections are asymptomatic or cause limited cutaneous symptoms, some give rise to serious central nervous system (CNS) manifestations. Both primary HSV infection and subsequent reactivation events can cause viral replication and spread within the brain, ultimately leading to pathologic inflammation and direct CNS damage. In addition to fulminant presentations of HSV encephalitis, subclinical HSV CNS infections have been implicated in neurodevelopmental, cognitive, and neurodegenerative impairment. Here, we review the pathogenesis of HSV infection and resulting CNS manifestations across the human lifespan. Identifying the mechanisms of HSV-induced CNS damage, and therefore the populations at highest risk for neurological morbidity, may provide a better understanding of the role viruses play in neurological diseases and inform novel approaches to treatment.

Herpes simplex virus (HSV) infection of the neonatal brain causes severe encephalitis and permanent neurologic deficits. However, infants infected with HSV at the time of birth follow varied clinical courses, with approximately half of infants experiencing only external infection of the skin rather than invasive neurologic disease. Understanding the cause of these divergent outcomes is essential to developing neuroprotective strategies. To directly assess the contribution of viral variation to neurovirulence, independent of human host factors, we evaluated clinical HSV isolates from neonates with different neurologic outcomes in neurologically relevant in vitro and in vivo models. We found that isolates taken from neonates with encephalitis are more neurovirulent in human neuronal culture and mouse models of HSV encephalitis, as compared to isolates collected from neonates with skin-limited disease. These findings suggest that inherent characteristics of the infecting HSV strain contribute to disease outcome following neonatal infection.

More than 14,000 neonates are infected with herpes simplex virus (HSV) annually. Approximately half display manifestations limited to the skin, eyes, or mouth (SEM disease). The rest develop invasive infections that spread to the central nervous system (CNS disease or encephalitis) or throughout the infected neonate (disseminated disease). Invasive HSV disease is associated with significant morbidity and mortality, but the viral and host factors that predispose neonates to these forms are unknown. To define viral diversity within the infected neonatal population, we evaluated 10 HSV-2 isolates from newborns with a range of clinical presentations. To assess viral fitness independently of host immune factors, we measured viral growth characteristics in cultured cells and found diverse in vitro phenotypes. Isolates from neonates with CNS disease were associated with larger plaque size and enhanced spread, with the isolates from cerebrospinal fluid (CSF) exhibiting the most robust growth. We sequenced complete viral genomes of all 10 neonatal viruses, providing new insights into HSV-2 genomic diversity in this clinical setting. We found extensive interhost and intrahost genomic diversity throughout the viral genome, including amino acid differences in more than 90% of the viral proteome. The genes encoding glycoprotein G (gG; US4), glycoprotein I (gI; US7), and glycoprotein K (gK; UL53) and viral proteins UL8, UL20, UL24, and US2 contained variants that were found in association with CNS isolates. Many of these viral proteins are known to contribute to cell spread and neurovirulence in mouse models of CNS disease. This report represents the first application of comparative pathogen genomics to neonatal HSV disease. IMPORTANCE Herpes simplex virus (HSV) causes invasive disease in half of infected neonates, resulting in significant mortality and permanent cognitive morbidity. The factors that contribute to invasive disease are not understood. This study revealed diversity among HSV isolates from infected neonates and detected the first associations between viral genetic variations and clinical disease manifestations. We found that viruses isolated from newborns with encephalitis showed enhanced spread in culture. These viruses contained protein-coding variations not found in viruses causing noninvasive disease. Many of these variations were found in proteins known to impact neurovirulence and viral spread between cells. This work advances our understanding of HSV diversity in the neonatal population and how it may impact disease outcome.