Pathophysiology
1) caused by infection with hepatitis B virus 2) occurs as acute (but usually self-limited), chronic (active and carrier states), and rarely fulminant variants 3) acute cases confer life-long immunity 4) in chronic cases, the virus is not cleared by the immune system – this can be asymptomatic (carrier state) or symptomatic if there is ongoing hepatocyte destruction (active state)
Signs and Symptoms
1) fever 2) anorexia/nausea/vomiting 3) abdominal pain 4) jaundice 5) fatigue
Characteristic Test Findings
Laboratory – 1) increased AST and ALT (400-4000 IU) 2) increased bilirubin 3) presence of surface antigen (before onset of symptoms and disappears during convalescence in acute variant 4) presence of antibody to surface antigen 5) presence of antibody to core antigen (at time of increased transaminases) 6) presence of e antigen after surface antigen appears and before it disappears (acute variant)
Histology/Gross Pathology
1) circular, large double-stranded DNA virus 2) contains four principal genes – core gene (codes for core antigen and e antigen), surface gene (codes for surface antigen), polymerase gene, and X gene
Associated Conditions
1) hepatocellular carcinoma 2) hepatitis D infection 3) surface antigen-antibody complexes can cause serum-like sickness, cryoglobulinemia, polyarteritis, and glomerulonephritis
Biochemistry
viral DNA replication occurs inside of hepatocyte via reverse transcriptase in an episome (does not insert into host DNA)
Inheritance/Epidemiology
1) transmission is via blood, saliva, and semen 2) 350 million chronic cases worldwide 3) 90% of chronic cases are male 4) incubation is 2-3 months
Treatment
1) hepatitis B vaccine as neonate 2) no treatment required other than supportive in acute, self-limited cases 3) lamivudine in chronic infection
Tips for USMLE
1) surface antigen is immunogenic but not infectious 2) first marker in blood is surface antigen (before clinical symptoms) 3) presence of surface antibody signals complete recovery and lifelong immunity 4) when e antigen is present, there is high viral replication and maximal infectivity 5) if chronic variant, the surface antigen will be present 6) uses a reverse transcriptase to replicate
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