Hepatitis B

Hepatitis B is an infectious disease of the liver caused by the hepatitis B virus (HBV), a small enveloped DNA virus classified taxonomically as a species within the genus Orthohepadnavirus of the family Hepadnaviridae. The pathogen is one of the smallest recognized animal viruses, measuring 30–42 nanometers in diameter, and possesses a characteristic icosahedral nucleocapsid enclosing a partially double-stranded DNA genome with reverse transcriptase activity. The infection can manifest as an acute, self-limited illness or progress to chronic carriage, with the latter defined by viral persistence beyond six months following initial exposure.

Acute hepatitis B infection presents with variable clinical manifestations, ranging from completely asymptomatic courses to fulminant hepatic failure. When symptomatic, the incubation period ranges from 30 to 180 days, with initial symptoms including nausea, vomiting, jaundice, fatigue, dark urine, and abdominal pain. The acute symptomatic phase typically persists for several weeks, though some individuals may experience prolonged illness lasting up to six months; mortality from acute infection is rare. Chronic hepatitis B infection, defined as persistence beyond six months, develops in approximately 90% of those infected perinatally or in early childhood, compared to fewer than 10% of those infected after age five. Most chronically infected individuals remain asymptomatic for decades, yet approximately 25% will eventually develop cirrhosis or hepatocellular carcinoma as complications of ongoing hepatic inflammation and fibrosis.

Hepatitis B constitutes a major global health burden, with substantial geographic variation in prevalence and chronic infection rates. The WHO Western Pacific Region bears the highest burden, with approximately 97 million people chronically infected, followed by the WHO African Region with 65 million affected individuals. The WHO South-East Asia Region accounts for 61 million chronic infections, while the Eastern Mediterranean, European, and Americas regions report 15 million, 11 million, and 5 million chronic infections, respectively. In highly endemic areas, infection is most commonly acquired through perinatal transmission from mother to child or through horizontal transmission among young children during the first five years of life, when the developing immune system fails to clear the virus effectively. The epidemiology reflects both historical patterns of universal childhood infection and ongoing transmission risks in populations with limited access to vaccination and blood safety measures.

Hepatitis B virus is transmitted through exposure to infectious blood and body fluids containing blood, including saliva, vaginal secretions, and semen. The virus is 50 to 100 times more infectious than HIV, reflecting its high environmental stability and low infectious dose. In highly endemic regions, perinatal transmission during childbirth represents the dominant mode of acquisition, with a 20% risk of transmission from HBsAg-positive mothers rising to 90% when the mother is also HBeAg-positive. Horizontal transmission among young children through bites, contaminated objects, or close household contact also contributes significantly to the endemic reservoir. In healthcare and community settings, transmission occurs through needlestick injuries, unsafe injection practices, tattooing, body piercing, and sharing of contaminated needles or sharp instruments. Sexual transmission and household contact with infected individuals represent additional routes in lower-prevalence settings.

Infants born to mothers with chronic hepatitis B infection face the highest risk of acquiring perinatal infection and subsequently developing chronic disease, with transmission risk substantially elevated when the mother is HBeAg-positive. Young children under five years of age are particularly susceptible to chronic infection following horizontal exposure, as immature immune function impairs viral clearance. Persons living with HIV demonstrate higher hepatitis B prevalence and accelerated liver disease progression, warranting integrated screening and treatment approaches. Healthcare workers and others occupationally exposed to blood and body fluids through needlestick injuries or mucosal contact face elevated exposure risk. Individuals with multiple sexual partners, people who inject drugs, and those receiving unsafe medical or cosmetic procedures involving contaminated equipment represent additional populations at increased risk of acquisition in lower-prevalence settings.

Hepatitis B is preventable through safe and effective vaccination, which provides nearly 100% protection against the virus. The WHO recommends that all infants receive the hepatitis B vaccine as soon as possible after birth, ideally within 24 hours, followed by two or three additional doses administered at least four weeks apart to complete the primary series. Complete vaccination confers long-term protection, with evidence suggesting immunity persists for at least 20 years and likely for life, eliminating the routine need for booster doses in immunocompetent individuals who have completed the three-dose series. Perinatal transmission can be further reduced through antiviral prophylaxis administered to infected mothers during late pregnancy, combined with passive and active immunoprophylaxis of the newborn. Blood safety measures, including universal screening of all blood donations for hepatitis B surface antigen, represent an essential secondary prevention strategy to prevent transfusion-transmitted infection.

Surveillance for hepatitis B relies primarily on laboratory confirmation, as clinical presentation cannot reliably distinguish HBV infection from other viral hepatitis agents. Diagnostic algorithms employ serological assays detecting viral antigens (particularly HBsAg as the primary screening marker) and host antibodies to distinguish acute from chronic infection and to assess disease stage and infectivity. The WHO recommends HBsAg screening of all blood donations to ensure blood safety and prevent iatrogenic transmission. Population-based surveillance typically monitors chronic infection prevalence through periodic serosurveys, while case-based surveillance tracks acute infections, perinatal exposure, and treatment outcomes. The integration of hepatitis B surveillance with HIV programs is particularly relevant given the 7.4% global prevalence of HBV coinfection among HIV-infected persons and the shared therapeutic agent tenofovir, which is active against both viruses.

1. 1 WHO Fact Sheet. Hepatitis B.
2. 2 Wikidata. Hepatitis B virus.
3. 3 Wikipedia. Hepatitis B - Wikipedia.

ICD-10

B16

ICD-11

1E50.1

Total cases

20.3M

Total deaths

8K

Peak month

2024-03

Coverage

3 reporting countries · 2000-01-01 → 2023-12-09