Hepatitis B: Comprehensive Lecture

What is Hepatitis B?

Hepatitis B is a DNA virus from the Hepadnaviridae family that infects over 350 million people worldwide, causing chronic liver disease, cirrhosis, and hepatocellular carcinoma, with an estimated 500,000-700,000 deaths annually. 1, 2

HBV is a small, partially double-stranded DNA virus with a 3.2 kb genome that replicates through an RNA intermediate, similar to retroviruses 2, 3
The virus can integrate into the host genome, conferring a distinct ability to persist in infected cells 3
HBV is concentrated most highly in blood and is approximately 100 times more infectious than HIV and 10 times more infectious than HCV 4
The virus remains infectious on environmental surfaces for at least 7 days 5

Transmission Routes

HBV is transmitted through percutaneous, mucosal, or nonintact skin exposure to infectious blood or body fluids, with perinatal transmission being the highest risk route (90% chronicity rate). 5

Primary Transmission Routes:

Perinatal transmission: 80-90% of infants infected at birth develop chronic infection 5
Sexual transmission: Efficient transmission occurs among heterosexuals and men who have sex with men (MSM) 5
Percutaneous exposure: Injection drug use and needlestick injuries 5
Horizontal transmission: 30% of children infected before age 6 develop chronic infection 5

Infectious Body Fluids:

Blood (highest concentration), semen, vaginal secretions 5
Saliva, tears, bile, cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, amniotic fluid 5
Urine, feces, vomitus, sputum, and sweat are NOT efficient transmission vehicles unless they contain blood 5
Breast milk contains HBsAg but is unlikely to transmit infection; breastfeeding is NOT contraindicated 5

Diagnosis and Serologic Markers

Diagnosis requires HBsAg testing to confirm current infection, with additional serologic markers (anti-HBs, anti-HBc IgM/IgG, HBeAg, anti-HBe) and HBV DNA quantification to classify disease phase and guide treatment. 5, 6, 7

Key Serologic Markers:

Marker	Interpretation
HBsAg positive	Current infection (acute or chronic); if persists >6 months = chronic [5,6]
Anti-HBs positive	Immunity from vaccination or resolved infection [5,8]
IgM anti-HBc positive	Acute infection [5]
IgG anti-HBc positive	Past or chronic infection [5]
HBeAg positive	High viral replication and infectivity [5]
Anti-HBe positive	Lower viral replication (but reversion can occur) [5]
HBV DNA	Measure of viral load and replication [5,6]

Diagnostic Algorithm:

Screen with HBsAg and anti-HBs to determine infection status and immunity 6
If HBsAg positive: Check HBeAg, anti-HBe, HBV DNA, and ALT to classify disease phase 5, 6
If HBsAg negative but anti-HBc positive: Check anti-HBs to distinguish resolved infection (anti-HBs positive) from occult infection (anti-HBs negative, may have detectable HBV DNA) 8
Assess liver fibrosis using non-invasive tests (transient elastography) or biopsy 6

Who Should Be Screened:

All persons born in endemic regions (Asia, Africa, Pacific Islands) 6
HIV-infected individuals, dialysis patients, healthcare workers 6
Pregnant women (universal screening) 5
Injection drug users and MSM 4, 5
Household and sexual contacts of HBsAg-positive persons 9

Natural History and Disease Phases

Chronic HBV infection progresses through four non-linear phases: immune tolerant, immune active, immune inactive, and reactivation, with 25% of chronically infected persons dying prematurely from cirrhosis or hepatocellular carcinoma. 5

Four Phases of Chronic HBV:

Immune Tolerant Phase (HBeAg-positive chronic infection):
- High HBV DNA (>20,000 IU/mL), normal ALT, positive HBeAg 5, 6
- Minimal hepatic inflammation or fibrosis 5
- Most chronically infected children remain in this phase until late childhood/adolescence 5
Immune Active Phase (HBeAg-positive or HBeAg-negative chronic hepatitis):
- Active immune response with hepatic inflammation ± fibrosis 5
- Prolonged immune active phase = high risk for cirrhosis and HCC 5
Immune Inactive Phase (Inactive carrier):
- Improvement of hepatic inflammation and fibrosis 5
- Lower HCC risk compared to active phase 5
Reactivation Phase:
- Active liver inflammation ± fibrosis 5
- Can occur with immunosuppressive therapy or HCV treatment 5

Risk Factors for Disease Progression:

Age at infection (younger = higher chronicity risk) 5, 10
Male sex, older age, HBV genotype 11, 10
Coinfection with HIV, HCV, or HDV 4, 10
Elevated ALT, alcohol use (>25-30 mL/day), tobacco use 9, 11, 10
Family history of HCC or cirrhosis 6, 10

Treatment Indications

All patients with cirrhosis and any detectable HBV DNA must be treated immediately, regardless of ALT levels; non-cirrhotic patients require treatment when HBV DNA ≥2,000 IU/mL with elevated ALT or evidence of at least moderate fibrosis. 6, 8

Immediate Treatment Required:

Decompensated cirrhosis with any detectable HBV DNA 6, 8
Compensated cirrhosis with HBV DNA >2,000 IU/mL, regardless of ALT 6, 8
Life-threatening disease (acute liver failure, severe acute hepatitis with coagulopathy) 6, 8
HBV DNA ≥20,000 IU/mL AND ALT ≥2× ULN (no biopsy needed) 6, 8

Treatment Considerations for Non-Cirrhotic Patients:

HBV DNA ≥2,000 IU/mL with elevated ALT (>40 IU/L) and at least moderate necroinflammation/fibrosis on biopsy 6, 8
HBV DNA ≥2,000 IU/mL with normal ALT if at least moderate fibrosis demonstrated (liver stiffness ≥9 kPa with normal ALT or ≥12 kPa with ALT <5× ULN) 6, 8
HBeAg-positive patients >30-40 years with persistently normal ALT and high HBV DNA may be treated regardless of histology 6, 8

Special Populations Requiring Treatment:

Pregnant women with HBV DNA >200,000 IU/mL: Start tenofovir DF at 24-32 weeks gestation to prevent perinatal transmission 5, 6, 8
Immunosuppressive therapy recipients (rituximab, anthracyclines, high-dose steroids): Start prophylaxis 2-4 weeks before therapy 8
Healthcare workers with HBV DNA ≥2,000 IU/mL performing exposure-prone procedures 6

Treatment Options

First-line treatment consists of nucleos(t)ide analogues with high genetic barriers to resistance: entecavir, tenofovir disoproxil fumarate (TDF), or tenofovir alafenamide (TAF), with long-term potentially indefinite therapy required in most patients. 11, 6, 8

First-Line Agents:

Agent	Dosing	Key Features	Resistance
Entecavir	0.5 mg daily	High potency, high barrier to resistance	<1% at 5 years [6]
Tenofovir DF (TDF)	300 mg daily	High potency, preferred in pregnancy	No resistance at 8 years [6]
Tenofovir AF (TAF)	25 mg daily	Less renal/bone toxicity than TDF	High barrier to resistance [6]

Avoid First-Generation NAs:

Lamivudine: High resistance rates (up to 70% at 5 years) 4, 8
Not recommended due to low potency and high resistance 6

Pegylated Interferon Alfa:

Finite-duration therapy (48 weeks) for selected patients with mild-to-moderate disease 6, 8
Higher rates of HBeAg and HBsAg loss compared to NAs, especially in genotype A 11
Absolutely contraindicated in decompensated cirrhosis and pregnancy 6, 8
Limited by side effects and variable response 6

Treatment Efficacy:

Viral suppression: 96.7% achieve undetectable HBV DNA with tenofovir at 2 years 11
HBeAg seroconversion: 27.3% at 10 years with tenofovir 11
HBsAg loss (functional cure): 3.4-4.9% at 10 years with tenofovir 11
Cirrhosis regression: 74% of cirrhotic patients show regression after 5 years of tenofovir 6

Treatment Monitoring

Monitor HBV DNA every 3 months until undetectable, then every 6 months; check liver enzymes every 3-6 months; and perform annual quantitative HBsAg testing to assess for functional cure. 6, 8

Monitoring Protocol During Treatment:

HBV DNA: Every 3 months until undetectable, then every 6 months 6, 8
ALT/AST: Every 3-6 months 6, 8
Quantitative HBsAg: Annually to assess for HBsAg loss 8
Renal function: If on tenofovir (especially TDF) 8
Bone mineral density: Consider if on TDF with risk factors 6

Monitoring for Patients NOT on Treatment:

ALT: At least every 3 months 6
HBV DNA: Every 6-12 months 6
Fibrosis assessment: Every 12 months using non-invasive tests 6

Treatment Response Definitions:

Virological response: Undetectable HBV DNA by sensitive PCR assay 6
Biochemical response: Normalization of ALT levels 6
Sustained off-therapy response: HBV DNA <2,000 IU/mL for ≥12 months after stopping therapy 6

Treatment Duration and Stopping Criteria

Long-term, potentially indefinite treatment is typically required with nucleos(t)ide analogues, with HBsAg loss being the optimal endpoint but rarely achieved; stopping therapy may be considered in HBeAg-positive patients who achieve HBeAg seroconversion with ≥12 months consolidation therapy. 11, 6, 8

Mandatory Lifelong Treatment:

All patients with decompensated cirrhosis 6
Compensated cirrhosis (stopping therapy risks decompensation) 6
Liver transplant recipients 6

Potential Stopping Criteria (Non-Cirrhotic Patients):

HBeAg-positive patients: HBeAg seroconversion + undetectable HBV DNA + ≥12 months consolidation therapy 6, 8
Optimal endpoint: HBsAg loss (functional cure), but rarely achieved (3-5% at 10 years) 11, 6
Close monitoring required after stopping: Most patients experience viral relapse 11

Hepatocellular Carcinoma Surveillance

Ultrasound examination every 6 months is mandatory for all cirrhotic patients and high-risk individuals (Asian men >40 years, Asian women >50 years, family history of HCC), even during effective antiviral therapy. 6, 8

High-Risk Groups Requiring HCC Surveillance:

All patients with cirrhosis (regardless of treatment status) 6, 8
Asian men >40 years 6, 8
Asian women >50 years 6, 8
Family history of HCC 6, 8
Age >40 years with persistent ALT elevation 8
Moderate-to-high HCC risk scores 6

Surveillance Protocol:

Ultrasound every 6 months 6, 8
Alpha-fetoprotein (AFP) measurement at baseline and periodically 9
Early detection allows for potentially curative interventions (ablation, resection, transplant) 9

Important Caveat:

Antiviral therapy reduces but does NOT eliminate HCC risk 11, 10
HBV replication is an independent predictor of HCC, along with male sex, older age, genotype, coinfections, elevated ALT, alcohol, and tobacco 6

Prevention Strategies

Universal hepatitis B vaccination for all infants within 24 hours of birth, combined with postexposure prophylaxis (HepB vaccine + HBIG) for infants born to HBsAg-positive mothers, achieves 90-95% prevention efficacy. 5, 1, 5, 12

Vaccination Strategy:

Universal infant vaccination within 24 hours of birth 1, 5
3-dose series for complete protection 5
90-95% effective in preventing chronic infection 1
Vaccine coverage: 85% worldwide (2019), up from 30% in 2000 5, 12

Postexposure Prophylaxis for Infants:

HepB vaccine + HBIG within 12 hours of birth for infants born to HBsAg-positive mothers 5
Reduces infection rate to 0.7-1.1% (from 30-85% without prophylaxis) 5
Post-vaccination testing at 9-18 months to confirm protection 6
Infants born to mothers with HBV DNA >200,000 IU/mL remain at highest risk despite prophylaxis 5

Maternal Antiviral Therapy:

Tenofovir DF starting at 24-32 weeks gestation for pregnant women with HBV DNA >200,000 IU/mL 5, 6
Further reduces perinatal transmission beyond vaccine + HBIG 5

Postexposure Prophylaxis for Adults:

Vaccine series initiated within 12-24 hours: 70-90% effective 4
Vaccine + HBIG for known nonresponders or high-risk exposures 4
HBIG alone within 7 days for percutaneous exposure in nonresponders 4
Sexual exposure: HBIG within 2 weeks for exposure to acute hepatitis B 4

Additional Preventive Measures:

Hepatitis A vaccination for all HBV-infected patients (coinfection increases mortality 5.6-29 fold) 9, 8
Alcohol abstinence counseling (>25-30 mL/day worsens liver disease) 9, 8
Screen for coinfections: HIV, HCV, HDV 8
Identify and vaccinate susceptible contacts of HBsAg-positive persons 9

Special Clinical Scenarios

Acute Hepatitis B:

>95% of immunocompetent adults recover spontaneously without antiviral therapy 6
Supportive care is the mainstay for uncomplicated acute infection 5
Antiviral therapy indicated for severe acute hepatitis (coagulopathy, severe jaundice, liver failure) with entecavir or tenofovir 5, 6
Fulminant hepatitis: Evaluate for liver transplantation + start nucleos(t)ide analogues 6

Immunosuppressive Therapy:

HBsAg-positive patients: Start prophylaxis 2-4 weeks before high-risk agents (rituximab, anthracyclines, high-dose steroids) 8
Reactivation risk: 12-50% without prophylaxis 8
Continue prophylaxis through treatment and for 12-24 months after completion (24 months for rituximab) 8
HBcAb-positive/HBsAg-negative patients: Prophylaxis preferred, or monitor monthly HBV DNA if high anti-HBs present 8

HIV-HBV Coinfection:

All coinfected patients should receive antiretroviral therapy including tenofovir (TDF or TAF), regardless of CD4 count 6, 8
TDF- or TAF-based ART regimens are mandatory 6

Occult Hepatitis B:

HBsAg negative but HBV DNA detectable 5
Can transmit infection 5
Requires HBV DNA testing for diagnosis 8

Common Pitfalls to Avoid

Diagnostic Pitfalls:

Do NOT rely solely on traditional ALT cutoffs to exclude liver disease—normal ALT by conventional criteria does NOT exclude significant necroinflammation or fibrosis 6
Transient HBsAg positivity can occur up to 18 days post-vaccination (52 days in hemodialysis patients)—clinically insignificant 5
Window period: IgM anti-HBc may be the only positive marker during acute infection when HBsAg has cleared but anti-HBs not yet developed 8

Treatment Pitfalls:

NEVER use lamivudine as first-line therapy due to high resistance rates 4, 8
NEVER delay treatment in patients with decompensated cirrhosis—immediate treatment required 6, 8
Pegylated interferon is ABSOLUTELY CONTRAINDICATED in decompensated cirrhosis and pregnancy 6, 8
Do NOT stop antiviral therapy in cirrhotic patients—lifelong treatment mandatory 6

Monitoring Pitfalls:

Do NOT assume HCC risk is eliminated with viral suppression—surveillance remains mandatory 11, 6
Do NOT forget renal monitoring with tenofovir, especially TDF 8
Do NOT miss the opportunity to vaccinate susceptible household and sexual contacts 9

Prevention Pitfalls:

Do NOT delay birth dose of HepB vaccine—must be given within 24 hours, preferably before hospital discharge 5
Do NOT forget post-vaccination testing for infants born to HBsAg-positive mothers at 9-18 months 6
Breastfeeding is NOT contraindicated in HBV-infected mothers 5

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