Hepatitis B virus (HBV), belonging to the Hepadnaviridae family.
Infection is transmitted from person to person by contact with infected body fluids. Sexual contact is an important mode of transmission, but infection is also transmitted by transfusion of contaminated blood or blood products or by use of contaminated needles or syringes for injections. There is also a risk of transmission through other skin-penetrating procedures, including acupuncture, piercing and tattooing. Perinatal transmission may occur from mother to baby. There is no insect vector or animal reservoir.
Nature of the disease
Most acute HBV infections are asymptomatic or cause mild symptoms, which are often unrecognized. Symptomatic acute disease occurs in about 1% of perinatally infected individuals, in 10% of children infected between 1 and 5 years of age, and in about 30% of individuals infected after the age of 5 years. Clinical acute hepatitis B has a gradual onset, with anorexia, abdominal discomfort, nausea, vomiting, arthralgia and rash, followed by the development of jaundice in some cases. In adults, about 1% of cases are fatal. Chronic HBV infection develops in <5% of HBV-infected adults but more often in young children and in the majority of those infected perinatally. In some cases of chronic HBV infection, cirrhosis and/or liver cancer develop later.
The endemicity of HBV in a population is described by the prevalence of HBsAg, an HBV-specific component found in the blood (and other body fluids) in both acute and chronic stages of the infection. HBV is found worldwide, but with differing levels of endemicity. The majority of the world’s population live in countries where the prevalence of HBsAg in the general population is high (≥8%) or intermediate (27%). In certain areas of North America, northern and western Europe, the southern cone of South America, Australia and New Zealand, prevalence of chronic HBV infection is relatively low (<2% ) (see map).
Risk for travellers
The risk depends on (1) the prevalence of HBV infection in the country or area of destination, (2) the extent of direct contact with blood or body fluids or of sexual contact with potentially infected individuals, and (3) the duration and type of travel. Principal risky activities include unprotected sexual intercourse with an infected person; health-care interventions (medical, dental, laboratory or other) that entail direct exposure to human blood or body fluids; receipt of a transfusion of blood that has not been tested for HBV; and exposure to needles (e.g. acupuncture, piercing, tattooing or injecting drug use) that have not been appropriately sterilized. In addition, transmission from HBV-positive to HBV-susceptible individuals may occur through direct contact between open skin lesions following a penetrating bite or scratch.
See under “HIV/AIDS and other sexually transmitted infections", Chapter 5.