Herpes simplex virus-2 (HSV-2) is periodically shed throughout the human genital tract. Although a high viral load correlates with the development of genital ulcers, shedding also commonly occurs even when ulcers are absent, allowing for silent transmission during coitus and contributing to high seroprevalence of HSV-2 worldwide. Frequent viral reactivation occurs within ganglia despite diverse and complementary host and viral mechanisms that predispose toward latency, suggesting that viral replication may be constantly occurring in a small minority of neurons at these sites. Within genital mucosa, the in vivo expansion and clearance rates of HSV-2 are extremely rapid. Resident dendritic cells and memory HSV-2 specific T cells persist at prior sites of genital tract reactivation and, in conjunction with prompt innate recognition of infected cells, lead to rapid containment of infected cells. The fact that immune responses usually control viral replication in genital skin before lesions develop provides hope that enhancing such responses could lead to effective vaccines and immunotherapies.
[Show abstract][Hide abstract] ABSTRACT: It is largely unknown why certain infected hosts shed Herpes Simplex Virus-2 (HSV-2) more frequently and have more severe disease manifestations than others. One idea is that different density or functional capacity of tissue resident effector memory CD8+ T-cells between infected persons may explain phenotypic variability. To generate hypotheses for contrasting shedding patterns in different infected hosts, a spatial mathematical model was employed to evaluate the effects of variability in tissue resident effector memory CD8+ T-cell response, and HSV-2 replication and spread, on viral shedding rate. Model simulations suggest that high levels of CD8+ T-cells in the mucosa do not necessarily indicate a protective phenotype but rather an effective response to recent shedding. Moreover, higher CD8+ T-cell expansion rate and lower viral replication rate, which correlate with better short-term control, may have only a minor impact on long-term shedding rates. Breakthrough shedding occurs under all sets of model parameter assumptions, because CD8+ T-cell levels only surpass a protective threshold in a minority of genital tract mucosal micro-regions. If CD8+ T-cell levels are artificially increased using an immunotherapeutic approach, better control of shedding is predicted to occur for at least a year. These results highlight the complex co-dependent relationship between HSV-2 and tissue resident CD8+ lymphocytes during the course of natural infection.
Frontiers in Immunology 07/2013; 4:209. DOI:10.3389/fimmu.2013.00209
[Show abstract][Hide abstract] ABSTRACT: Genital herpes is an incurable, chronic disease that affects millions of people worldwide. Not only does genital herpes cause painful, recurrent symptoms, it is also a significant risk factor for the acquisition of other sexually transmitted infections such as HIV-1. Antiviral drugs are used to treat herpes simplex virus (HSV) infection, but they cannot stop viral shedding and transmission. Thus, developing a vaccine that can prevent or clear infection will be crucial in limiting the spread of disease. In this review we outline recent studies that improve our understanding of host responses against HSV infection, discuss past clinical vaccine trials, and highlight new strategies for vaccine design against genital herpes.
Trends in Immunology 09/2013; 34(10). DOI:10.1016/j.it.2013.08.001 · 10.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Genital herpes has a high global prevalence and burden of disease. This manuscript highlights recent advances in our understanding of genital herpes simplex virus (HSV) infections.
Studies demonstrate a changing epidemiological landscape with an increasing proportion of genital herpes cases associated with HSV type 1. There is also growing evidence that the majority of infected individuals exhibit frequent, brief shedding episodes that are most often asymptomatic, which likely contribute to high HSV transmission rates. Given this finding as well as readily available serological assays, some have proposed that routine HSV screening be performed; however, this remains controversial and is not currently recommended. Host immune responses, particularly local CD4 and CD8 T cell activity, are crucial for HSV control and clearance following initial infection, during latency and after reactivation. Prior HSV immunity may also afford partial protection against HSV reinfection and disease. Although HSV vaccine trials have been disappointing to date and existing antiviral medications are limited, novel prophylactic and therapeutic modalities are currently in development.
Although much remains unknown about genital herpes, improved knowledge of HSV epidemiology, pathogenesis and host immunity may help guide new strategies for disease prevention and control.
Current Opinion in Infectious Diseases 12/2013; 27(1). DOI:10.1097/QCO.0000000000000029 · 5.01 Impact Factor
C Morabito, P Lanuti, G A Caprara, S Guarnieri, V Verratti, G Ricci, A Catizone, M Marchisio, G Fanò-Illic, M A Mariggiò
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