TWiV 1163: Hepadnaviridae in the Heartland - A Discussion on Hepatitis B Virus (HBV)
0:00 Introduction: This episode of This Week in Virology (TWiV) was recorded at the 2024 International HBV Meeting in Chicago.
7:12 HBV Foundation: The HBV Foundation is a leading patient advocacy group focusing on education, lobbying, and linking individuals to care.
8:57 MicrobeTV: MicrobeTV, a non-profit, produces science podcasts like TWiV and relies on listener donations.
9:28 HBV Research: Mala Maini's research focuses on understanding the immune response to HBV, particularly in the liver, aiming to develop immunotherapies.
10:48 HBV Replication and Drug Discovery: John Tavis's lab studies HBV replication, focusing on the reverse transcriptase enzyme and developing drugs that inhibit its activity.
11:36 HBV Disease Overview: HBV infection can be acute or chronic. Acute infections are often asymptomatic, while chronic infections (more common in infants) can lead to liver inflammation, fibrosis, cirrhosis, and hepatocellular carcinoma (HCC), a major cause of cancer deaths.
14:17 HBV Transmission: HBV is primarily transmitted from mother to child during birth, but also through sexual contact and contaminated needles.
15:12 HBV Prevalence: Chronic HBV affects an estimated 270-300 million people globally, mainly in Southeast Asia and Sub-Saharan Africa.
16:39 Public Health Impact: HBV carries significant social stigma and impacts employment and movement in some countries. Guilt associated with mother-to-child transmission is also a significant emotional burden.
18:18 Misinformation: HBV is a target of misinformation campaigns, such as claims that it's solely a sexually transmitted disease, making public health efforts challenging.
18:47 HBV Particle Structure: The HBV particle consists of an envelope with surface glycoproteins, a capsid, and a partially double-stranded DNA genome. It also produces non-infectious subviral particles that can interfere with the immune response.
20:45 HBV Replication Cycle: HBV enters liver cells, repairs its DNA, and uses it as a template for viral transcripts. Reverse transcription occurs in the cytoplasm, and new viral particles are secreted without killing the host cell.
24:52 HBV Infection Efficiency: Even a small infectious dose can infect a large portion of the liver.
25:30 HBV Cell Specificity: HBV primarily infects hepatocytes (liver cells) but may also infect lymphocytes to a lesser extent.
26:25 HBV Integration and HCC: HBV DNA can integrate into the host cell's genome, potentially disrupting genes, promoting inflammation, and contributing to the development of HCC.
29:03 HBV Immunology (Acute Infection): HBV is a "stealth virus" that initially triggers a weak innate immune response. Adaptive immunity, primarily through CD4 and CD8 T cells, is crucial for resolving acute infections.
30:27 HBV Immunology (Chronic Infection): Chronic HBV infection is characterized by a dysfunctional immune response, with exhausted T cells, B cells, and NK cells. The liver's tolerogenic environment contributes to this dysfunction.
36:32 HBV Model Systems: Studying HBV is challenging due to limited model systems. Duck Hepatitis B Virus (DHBV) has been valuable for understanding molecular biology, but true HBV infection in immunocompetent animal models is difficult to achieve.
41:08 HBV Therapies: Current frontline therapies are nucleoside/nucleotide analogs that inhibit viral replication but are not curative. New therapies include capsid assembly modifiers, RNAse H inhibitors, and siRNA/antisense oligonucleotides.
43:27 Standard Therapy: The standard therapy is monotherapy with nucleoside analogs, typically used in chronic infections with overt liver damage.
46:28 Underdiagnosis and Undertreatment: A significant portion of HBV infections are undiagnosed and untreated, particularly in resource-limited settings.
47:04 Immune-Based Therapies: Interferon-alpha has been used as an immune-based therapy and is being revisited in combination with newer antivirals. Therapeutic vaccines are also being explored to stimulate new immune responses.
48:31 Functional Cure: A functional cure involves suppressing viral markers (s antigen and HBV DNA) to undetectable levels after treatment withdrawal, mimicking natural clearance but not eliminating all viral DNA.
50:44 HBV Vaccines: Preventative vaccines based on the surface antigen are available and highly effective in preventing infection. They are recommended for all newborns but face implementation challenges. Therapeutic vaccines are under development to boost immune responses in chronic infections.