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 potential 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 HBV infections are asymptomatic or cause mild symptoms, which are often unrecognized. Symptomatic 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 hepatitis 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 hepatitis B 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. Hepatitis B is found worldwide, but with differing levels of risk. 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 (less than 2% of the general population is HBsAg-positive) (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 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.
The vaccine should be considered for all non-immune individuals travelling to countries or areas with moderate to high risk of infection. It can be administered to infants from birth. Also see Precautions under “HIV/AIDS and other sexually transmitted infections”, Chapter 5.