The human hepatitis delta virus (HDV) is a satellite RNA virus that depends on hepatitis B virus (HBV) surface proteins (HBsAg) to assemble into infectious virions targeting the same organ (liver) as HBV. Until recently, the evolutionary origin of HDV remained largely unknown. The application of bioinformatics on whole sequence databases lead to discoveries of HDV-like agents (DLA) and shed light on HDV\'s evolution, expanding our understanding of HDV biology. DLA were identified in heterogeneous groups of vertebrates and invertebrates, highlighting that the evolution of HDV, represented by eight distinct genotypes, is broader and more complex than previously foreseen. In this study, we focused on the characterization of three mammalian DLA discovered in woodchuck (Marmota monax), white-tailed deer (Odocoileus virginianus), and lesser dog-like bat (Peropteryx macrotis) in terms of replication, cell-type permissiveness, and spreading pathways. We generated replication-competent constructs expressing 1.1-fold over-length antigenomic RNA of each DLA. Replication was initiated by transfecting the cDNAs into human (HuH7, HeLa, HEK293T, A549) and non-human (Vero E6, CHO, PaKi, LMH) cell lines. Upon transfection and replication establishment, none of the DLA expressed a large delta antigen. A cell division-mediated viral amplification assay demonstrated the capability of non-human DLA to replicate and propagate in hepatic and non-hepatic tissues, without the requirement of envelope proteins from a helper virus. Remarkably L-HDAg but not S-HDAg from HDV can artificially mediate envelopment of WoDV and DeDV ribonucleoproteins (RNPs) by HBsAg to form infectious particles, as demonstrated by co-transfection of HuH7 cells with the respective DLA expression constructs and a plasmid encoding HBV envelope proteins. These chimeric viruses are sensitive to HDV entry inhibitors and allow synchronized infections for comparative replication studies. Our results provide a more detailed understanding of the molecular biology, evolution, and virus-host interaction of this unique group of animal viroid-like agents in relation to HDV.

Chronic infection of hepatitis B virus (HBV) and hepatitis D virus (HDV) causes the most severe form of viral hepatitis. Due to the dependence on HBV, HDV was deemed to co-evolve and co-migrate with HBV. However, we previously found that the naturally occurred HDV/HBV combinations do not always reflect the most efficient virological adaptation (Wang et al., 2021). Moreover, regions with heavy HBV burden do not always correlate with high HDV prevalence (e.g., East Asia), and vice versa (e.g., Central Asia). Herein, we systematically elucidated the spatiotemporal evolutionary landscape of HDV to understand the unique epidemic features of HDV. We found that the MRCA of HDV was from South America around the late 13th century, was globally dispersed mainly via Central Asia, and evolved into eight genotypes from the 19th to 20th century. In contrast, the MRCA of HBV was from Europe ∼23.7 thousand years ago (Kya), globally dispersed mainly via Africa and East Asia, and evolved into eight genotypes ∼1100 years ago. When HDV stepped in, all present-day HBV genotypes had already formed and its global genotypic distribution had stayed stable geographically. Nevertheless, regionalized HDV adapted to local HBV genotypes and human lineages, contributing to the global geographical separation of HDV genotypes. Additionally, a sharp increase in HDV infections was observed after the 20th century. In conclusion, HDV exhibited a distinct spatiotemporal distribution path compared with HBV. This unique evolutionary relationship largely fostered the unique epidemic features we observe nowadays. Moreover, HDV infections may continue to ramp up globally, thus more efforts are urgently needed to combat this disease.

BACKGROUND: Existing research has provided evidence of changes in hepatitis delta virus (HDV) prevalence worldwide. This study aimed to investigate the prevalence and molecular characteristics of HDV to elucidate its spread in China.
METHODS: A total of 3,000 samples were collected from 2,241 HBV monoinfections and 759 HBV/HIV-1 coinfections across 13 sites in northern, southern, western, and southwestern China. Serological and virological prevalence were determined by detecting anti-HDV antibodies and HDV RNA.
RESULTS: The study revealed a 2.63% (95% CI: 2.06-3.21) seroprevalence of HDV among HBV infections in China, exhibiting regional variation. HDV seroprevalence was notably higher at 7.91% (95% CI: 5.98-9.83) in HBV and HIV-1 coinfections. Region and HIV-1 infection were identified as risk factors for HDV infection. Virological prevalence was 0.67% (95% CI: 0.38-0.96) in HBV infections and 2.24% (95% CI: 1.18-3.29) in HBV/HIV-1 coinfections. The predominant HDV genotype in China was HDV-2a, followed by HDV-1. Participants with anti-HDV positivity demonstrated significantly higher proportions of abnormal liver dysfunction and elevated HBV DNA load (P < 0.001) compared to anti-HDV-negative participants.
CONCLUSIONS: This study highlights the HDV epidemic in China, sheds light on its geographical distribution and high-risk populations, and provides insights for developing strategies to manage the spread of HDV in the country.

Due to the limited host range of HBV, research progress has been hindered by the absence of a suitable animal model. The natural history of woodchuck hepatitis virus (WHV) infection in woodchuck closely mirrors that of HBV infection in human, making this species a promising candidate for establishing both in vivo and in vitro HBV infection models. Therefore, this animal may be a valuable species to evaluate HBV vaccines and anti-HBV drugs. A significant milestone in HBV and hepatitis D virus (HDV) infection is the discovery of sodium taurocholate cotransporting polypeptide (NTCP) as the functional receptor. In an effort to enhance susceptibility to HBV infection, we introduced hNTCP into the woodchuck hepatocytes by multiple approaches including transduction of vLentivirus-hNTCP in woodchuck hepatocytes, transfection of p-lentivirus-hNTCP-eGFP plasmids into these cells, as well as transduction of vAdenovirus-hNTCP-eGFP. Encouragingly, our findings demonstrated the successful introduction of hNTCP into woodchuck hepatocytes. However, it was observed that these hNTCP-expressing hepatocytes were only susceptible to HDV infection but not HBV. This suggests the presence of additional crucial factors mediating early-stage HBV infection that are subject to stringent species-specific restrictions.

Hepatitis D virus (HDV) infection occurs as a coinfection with hepatitis B and increases the risk of hepatocellular carcinoma, decompensated cirrhosis, and mortality compared to hepatitis B virus (HBV) monoinfection. Reliable estimates of the prevalence of HDV infection and disease burden are essential to formulate strategies to find coinfected individuals more effectively and efficiently. The global prevalence of HBV infections was estimated to be 262,240,000 in 2021. Only 1,994,000 of the HBV infections were newly diagnosed in 2021, with more than half of the new diagnoses made in China. Our initial estimates indicated a much lower prevalence of HDV antibody (anti-HDV) and HDV RNA positivity than previously reported in published studies. Accurate estimates of HDV prevalence are needed. The most effective method to generate estimates of the prevalence of anti-HDV and HDV RNA positivity and to find undiagnosed individuals at the national level is to implement double reflex testing. This requires anti-HDV testing of all hepatitis B surface antigen-positive individuals and HDV RNA testing of all anti-HDV-positive individuals. This strategy is manageable for healthcare systems since the number of newly diagnosed HBV cases is low. At the global level, a comprehensive HDV screening strategy would require only 1,994,000 HDV antibody tests and less than 89,000 HDV PCR tests. Double reflex testing is the preferred strategy in countries with a low prevalence of HBV and those with a high prevalence of both HBV and HDV. For example, in the European Union and North America only 35,000 and 22,000 cases, respectively, will require anti-HDV testing annually.

About ten years ago, Wenhui Li\'s research group in China identified the sodium taurocholate co-transporting polypeptide (NTCP), a bile acid transporter predominantly expressed in the liver, as a functional receptor for hepatitis B virus (HBV) and its satellite hepatitis delta virus (HDV) through biochemical and genetic studies. This finding unraveled a longtime mystery in the HBV field and led to the establishment of efficient and easy-to-use HBV infection models, which paved the way for the in-depth study of the HBV entry mechanism and facilitated the development of therapeutics against HBV and HDV. The whole picture of the complex HBV entry process became clear upon the follow-up studies over the years, including the recent resolution found for the NTCP structure. As one of the first authors of the 2012 eLife paper on NTCP identification, here, I (H. Y.) share our experience on the bumpy and exciting journey of receptor hunting, particularly on the photo-cross-linking study and some detailed descriptions of the \"fishing\" process and summarize the key factors for our successful receptor identification. This review may also provide helpful insights for identifying a protein target by peptide or protein baits through cross-linking and immunoprecipitation.

Hepatitis delta virus (HDV) is a satellite RNA virus that relies on hepatitis B virus (HBV) for transmission. HIV/HBV/HDV coinfection or triple infection is common and has a worse prognosis than monoinfection.
We aimed to reveal the epidemiological characteristics of HIV/HBV/HDV triple infection in the global population.
A systematic literature search in PubMed, Embase, and the Cochrane Library was performed for studies of the prevalence of HIV/HBV/HDV triple infection published from January 1, 1990, to May 31, 2021. The Der Simonian-Laird random effects model was used to calculate the pooled prevalence.
We included 14 studies with 11,852 participants. The pooled triple infection rate in the global population was 7.4% (877/11,852; 95% CI 0.73%-29.59%). The results of the subgroup analysis showed that the prevalence of triple infection was significantly higher in the Asian population (214/986, 21.4%; 95% CI 7.1%-35.8%), in men (212/5579, 3.8%; 95% CI 2.5%-5.2%), and in men who have sex with men (216/2734, 7.9%; 95% CI 4.3%-11.4%). In addition, compared with people living with HIV, the HIV/HBV/HDV triple infection rate was higher in people with hepatitis B.
This meta-analysis suggests that the prevalence of HIV/HBV/HDV triple infection in the global population is underestimated, and we should focus more effort on the prevention and control of HIV/HBV/HDV triple infection.
PROSPERO CRD42021273949; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=273949.

Elite athletes who participate in contact sports are at risk of bleeding injuries, leading to transmission of blood-borne viruses including hepatitis type B, C and D (HBV, HCV and HDV) capable of causing chronic liver disease, liver failure and liver cancer. In view of the significant advances in the viral hepatitis field over the past decade, more structured approaches should be in place to screen for and manage viral hepatitis in elite athletes. HBV status should be assessed in all elite athletes, and those infected should receive nucleos(t)ide analogues for viral suppression, while uninfected individuals should receive HBV vaccination. The all-oral direct acting antivirals for HCV are highly effective and safe, thus the remaining challenge with hepatitis C is case identification and linkage to care. HDV is only found in HBV-infected individuals, which is characterized by rapid disease progression and higher rates of cirrhosis and liver cancer in infected subjects. Pegylated interferon was the mainstay of treatment for HDV infection until bulevirtide, a viral entry inhibitor, was recently approved by the European Union (EMA) and FDA in America, while multiple novel therapies are already in clinical trials as part of the HBV cure program. Overall, awareness of chronic viral hepatitis in athletes should be improved. Prevention remains the cornerstone of the management of viral hepatitis in sport coupled with rigorous disease assessment in infected individuals, and antiviral therapy where indicated.

Hepatitis D is the most severe form of human viral hepatitis and currently lacks an efficient therapy. Dendritic cell-derived exosomes (Dexs) have been found to induce immune responses capable of eliminating viruses. However, the therapeutic potential of antigen-loaded exosomes in hepatitis D is still unknown. Recently, we designed exosomes loaded with ubiquitinated hepatitis delta virus (HDV) small delta antigen (Ub-S-HDAg) and then treated mice bearing replicating HDV with these exosomes to explore their antiviral effect and mechanism. Mature dendritic cell-derived exosomes (mDexs) were loaded with Ub-S-HDAg and their antivirus function was evaluated in mice with HDV viremia. Furthermore, the proportion of CD8+ cells, the ratio of Th1/Th2 cells, the postimmunization levels of cytokines were explored, and the Janus kinases (JAK)/signal transducer and activator of transcription (STAT) pathway was evaluated with a JAK2 inhibitor AG490. In Ub-S-HDAg-Dexs group, the HDV RNA viral load was significantly decreased compared with other groups by CD8+ cell enrichment and an increase Th1/Th2 cell ratio. Furthermore, lymphocyte infiltration was increased, while the HDAg level was decreased in mouse liver tissue. However, there were no significant differences in HBV surface antigen (HBsAg), alanine aminotransferase (ALT), or aspartate aminotransferase (AST) levels among the groups. Moreover, p-JAK2, p-STAT1, p-STAT4, STAT1, and STAT4 expression was increased in Ub-S-HDAg-Dexs group. In conclusion, Ub-S-HDAg-Dexs might be a potential immunotherapeutic agent for eradicating HDV by inducing specific cellular immune response via the JAK/STAT pathway. IMPORTANCE Hepatitis D is the most severe viral hepatitis with accelerating the process of liver cirrhosis and increasing the risk of hepatocellular carcinoma. However, there are no effective antiviral drugs. Exosomes derived from mature dendritic cells are used not only as immunomodulators, but also as biological carriers to deliver antigens to induce robust immune response. Based on these properties, exosomes could be used as a biological immunotherapy by enhancing adaptive immune response to inhibit hepatitis D virus replication. Our research may provide a new therapeutic strategy to eradicate HDV in the future.

Hepatitis delta virus (HDV) is an obligate satellite of hepatitis B virus (HBV). HIV/HDV co-infection is associated with a high rate of hepatic decompensation events and death. We aimed to characterize the epidemiology of HDV infection in HIV/HBV co-infected individuals. We systematically searched PubMed, Embase, Cochrane Library, Web of Science, CINAHL and Scopus for studies published from 1 Jan 2002 to 7 May 2018 measuring prevalence of HDV among the HIV population. Pooled seroprevalence was calculated with the DerSimonian-Laird random-effects model. Our search returned 4624 records, 38 of which met the inclusion and exclusion criteria. These studies included data for 63 cohorts from 18 countries and regions. The overall HDV seroprevalence of HIV-infected individuals was 1.03% (95% CI 0.43-1.85) in 2002-2018 globally. Moreover, the estimated pooled HDV seroprevalence among the general population was 1.07% (95% CI 0.65-1.59) in 2002-2018, which was not significantly different from the HDV seroprevalence of individuals living with HIV (p = 0.951). The overall HDV seroprevalence of the HBsAg positive population was 12.15% (95% CI 10.22-14.20), p = 0.434 when compared with the corresponding data of HIV/HBV co-infected individuals. This meta-analysis suggested that there was no difference between the HDV seroprevalence in HIV-infected individuals and the general population.