The vehicle of HBV transmission was assumed to be blood from damaged rectal mucosa. However, it is now recognized that heterosexual transmission accounts for an even larger and increasing proportion of HBV infections. Blood from minor lesions, semen and vaginal secretions are considered to be likely vehicles for infection. Semen has been shown to be infectious and HBsAg has been detected in vaginal secretions. These studies have also shown that heterosexuals with multiple partners, and those with a history of other sexually transmitted diseases, are at increased risk of infection.
Sexual transmission is a form of horizontal transmission.
This is the best understood mode of HBV transmission. Infection can be spread if these media are splashed onto damaged skin or mucous membranes, or are transfused. Contaminated surgical instruments and other utensils are another possible hazard. This mode of transmission occurs in all parts of the world. In areas of low endemicity, it is considered to be particularly important, because perinatal transmission is less common.