Hepatitis B Virus - HBV

 

Clinical Background

Hepatitis B (HBV) is a blood-borne virus and one of the most common infectious diseases in the world.

Epidemiology

  • Incidence
    • Endemic in Asia, sub-Saharan Africa
    • 1/100,000 in U.S. (2004 statistics)
  • Transmission
    • Parenteral – common infection route in low-prevalence regions
    • Sexual – common infection route in low-prevalence regions
    • Vertical perinatal – main infection route in endemic regions
    • Horizontal – from chronically infected person in a household
  • Ethnicity – more common in Alaskan native population

Organism

  • DNA virus of Hepadnaviridae family
  • Eight HBV subgroups (A-H) based on genetic differences
    • Genotype A most common in U.S.
    • Genotype may be associated with disease progression and response to treatment
  • Infection not directly cytotoxic to hepatocytes
    • Severity of injury is modulated by host immune responses

Risk Factors

  • Parenteral drug abuse
  • Multiple sex partners (more than 1 partner during the preceding 6 months)
  • Sexual transmission from HBV-positive partner
  • Infants of HBV-infected mothers
  • Persons infected with human immunodeficiency virus (HIV)
  • High rates of HBV infection continue to occur among Alaskan native and Pacific Islander children and among children residing in households of first-generation immigrants from countries where HBV infection is endemic
  • Needlestick
    • 1-6% risk if blood is HBV surface antigen positive
    • 22-40% risk if blood is HBV surface antigen and e antigen positive
  • Hemodialysis

Pathophysiology

  • Phases of chronic HBV
    • Immune tolerance
      • Positive e antigen, negative e antibody, HBV DNA high, normal transaminases
    • Immune active
      • Positive e antigen, negative e antibody, moderately high HBV DNA, elevated transaminases
    • Inactive carriers
      • Negative e antigen, positive e antibody, absent or low HBV DNA, normal transaminases
    • Reactivation
      • Negative or positive e antigen, positive or negative e antibody, moderately high HBV DNA, elevated transaminases
  • Infants and young children are at the greatest risk for becoming chronically infected if exposed to the hepatitis B virus
    • 90% of exposed infants will develop chronic hepatitis
    • 30% of exposed children ages 1-5 will develop chronic hepatitis
    • Only 5% of exposed adults will develop chronic hepatitis

Clinical Presentation

  • Acute HBV
    • Incubation period of 2 weeks to 4 months
      • Approximately 50% of those infected usually have symptoms appear 25 to 180 days following exposure
    • The mildest attacks are asymptomatic anicteric and detectable only by an increase in serum transaminase levels
    • Influenza-like symptoms – fatigue, malaise, fever, anorexia
    • Jaundice and gastrointestinal symptoms (usually within 10 days of symptom onset)
    • A few develop acute fulminant hepatic failure requiring transplantation
      • Rapidly progressive hepatitis with signs of liver failure – coagulopathy, encephalopathy, cerebral edema
  • Most common findings are fatigue or vague, right-upper quadrant discomfort
  • Patients may have systemic symptoms that are associated with the deposition of circulating hepatitis B antigen-antibody immune complexes such as arthritis, leukocytoclastic vasculitis, glomerulonephritis, cryoglobulinemia and generalized vasculitis
  • Long-term consequences include cirrhosis and hepatocellular carcinoma
    • Cirrhosis may present with jaundice, ascites, splenomegaly, encephalopathy or variceal bleeding

Treatment

  • Current therapies are available
    • May be curative or significantly reduce viral load in chronic hepatitis
    • Reduces risk of hepatocellular carcinoma

Prevention

  • Vaccination is recommended for:
    • Persons who reside in a community with an increased prevalence of infection
    • Persons who will travel to a country with high prevalence rates
    • Health care workers
    • All neonates and children
    • HIV-positive patients
    • Prisoners