Natural killer cells can act as rheostats, or ‘master regulators’, controlling antiviral T-cell responses. In mice infected with lymphocytic choriomeningitis virus, a model for human hepatitis C virus and human immunodeficiency virus (HIV) infections, natural killer (NK) T cells are shown to regulate antiviral T-cell immunity by directly killing activated CD4 T cells. This immunoregulatory role is in addition to the direct antiviral effects of NK cells. Antiviral T cells are thought to regulate whether hepatitis C virus (HCV) and human immunodeficiency virus (HIV) infections result in viral control, asymptomatic persistence or severe disease, although the reasons for these different outcomes remain unclear. Recent genetic evidence, however, has indicated a correlation between certain natural killer (NK)-cell receptors and progression of both HIV and HCV infection1,2,3, implying that NK cells have a role in these T-cell-associated diseases. Although direct NK-cell-mediated lysis of virus-infected cells may contribute to antiviral defence during some virus infections—especially murine cytomegalovirus (MCMV) infections in mice and perhaps HIV in humans4,5—NK cells have also been suspected of having immunoregulatory functions. For instance, NK cells may indirectly regulate T-cell responses by lysing MCMV-infected antigen-presenting cells6,7. In contrast to MCMV, lymphocytic choriomeningitis virus (LCMV) infection in mice seems to be resistant to any direct antiviral effects of NK cells5,8. Here we examine the roles of NK cells in regulating T-cell-dependent viral persistence and immunopathology in mice infected with LCMV, an established model for HIV and HCV infections in humans. We describe a three-way interaction, whereby activated NK cells cytolytically eliminate activated CD4 T cells that affect CD8 T-cell function and exhaustion. At high virus doses, NK cells prevented fatal pathology while enabling T-cell exhaustion and viral persistence, but at medium doses NK cells paradoxically facilitated lethal T-cell-mediated pathology. Thus, NK cells can act as rheostats, regulating CD4 T-cell-mediated support for the antiviral CD8 T cells that control viral pathogenesis and persistence.

In October 2018 a large number of international experts with complementary expertise came together in Taormina to participate in a workshop on occult hepatitis B virus infection (OBI). The objectives of the workshop were to review the existing knowledge on OBI, to identify issues that require further investigation, to highlight both existing controversies and newly emerging perspectives, and ultimately to update the statements previously agreed in 2008. This paper represents the output from the workshop.

The coronavirus disease 2019 (COVID-19) pandemic poses an enormous challenge to healthcare systems in affected communities. Older patients and those with pre-existing medical conditions have been identified as populations at risk of a severe disease course. It remains unclear at this point to what extent chronic liver diseases should be considered as risk factors, due to a shortage of appropriate studies. However, patients with advanced liver disease and those after liver transplantation represent vulnerable patient cohorts with an increased risk of infection and/or a severe course of COVID-19. In addition, the current pandemic requires unusual allocation of healthcare resources which may negatively impact the care of patients with chronic liver disease that continue to require medical attention. Thus, the challenge hepatologists are facing is to promote telemedicine in the outpatient setting, prioritise outpatient contacts, avoid nosocomial dissemination of the virus to patients and healthcare providers, and at the same time maintain standard care for patients who require immediate medical attention.

Background and Aim: Decisions on public health issues are dependent on reliable epidemiological data. A comprehensive review of the literature was used to gather country‐specific data on risk factors, prevalence, number of diagnosed individuals and genotype distribution of the hepatitis C virus (HCV) infection in selected European countries, Canada and Israel.Methodology: Data references were identified through indexed journals and non‐indexed sources. In this work, 13 000 articles were reviewed and 860 were selected based on their relevance.Results: Differences in prevalence were explained by local and regional variances in transmission routes or different public health measures. The lowest HCV prevalence (≤0.5%) estimates were from northern European countries and the highest (≥3%) were from Romania and rural areas in Greece, Italy and Russia. The main risk for HCV transmission in countries with well‐established HCV screening programmes and lower HCV prevalence was injection drug use, which was associated with younger age at the time of infection and a higher infection rate among males. In other regions, contaminated glass syringes and nosocomial infections continue to play an important role in new infections. Immigration from endemic countries was another factor impacting the total number of infections and the genotype distribution. Approximately 70% of cases in Israel, 37% in Germany and 33% in Switzerland were not born in the country. In summary, HCV epidemiology shows a high variability across Europe, Canada and Israel.Conclusion: Despite the eradication of transmission by blood products, HCV infection continues to be one of the leading blood‐borne infections in the region.

Summary: The disease burden of hepatitis C virus (HCV) is expected to increase as the infected population ages. A modelling approach was used to estimate the total number of viremic infections, diagnosed, treated and new infections in 2013. In addition, the model was used to estimate the change in the total number of HCV infections, the disease progression and mortality in 2013–2030. Finally, expert panel consensus was used to capture current treatment practices in each country. Using today's treatment paradigm, the total number of HCV infections is projected to decline or remain flat in all countries studied. However, in the same time period, the number of individuals with late‐stage liver disease is projected to increase. This study concluded that the current treatment rate and efficacy are not sufficient to manage the disease burden of HCV. Thus, alternative strategies are required to keep the number of HCV individuals with advanced liver disease and liver‐related deaths from increasing.