This is an infectious disease, caused by the hepatitis B virus (Human Hepatitis B Virus, HBV), from the Hepadnavirus family.
The virus is transmitted through the blood and biological fluids of infected individuals (blood, breast milk, sperm, vaginal secretions). The infection can be transmitted through contact with infected blood. The virus can penetrate the body via even minor lesions of the skin and mucous membranes through the use of contaminated objects such as toothbrushes, scissors, and razors. The virus can also be transmitted sexually and from mother to child during birth.
Symptoms and complications
The incubation of the virus lasts approximately 90 days, but this can vary greatly (from 30 to 180 days). HBV infection can manifest in different ways:
- acute hepatitis: this presents with malaise, fever, jaundice, nausea, vomiting, however, in some cases it is asymptomatic. It occurs in 1% of perinatal infections, in 10% of children aged between 1 and 5, and in 30% of HBV infections in patients older than 5 years.
- fulminant hepatitis: rapidly worsening, in 90% of cases a liver transplant is required. It develops in 0.1-0.6% of acute hepatitis cases.
- chronic hepatitis: this presents with progressively worsening liver failure and little clinical symptomatology at the beginning. Progressively the liver can degenerate into steatosis, necrosis, up to the point of liver cirrhosis and functional failure of the organ. Chronic HBV infection also carries a high risk of liver cancer.
Indicatively, 5% of HBV infected patients will contract chronic hepatitis and the characteristics of the disease progression depend on the age at which the virus is contracted: in adulthood, acute infection without chronicity is found in 90% of cases, while in childhood 90% will develop a chronic form, in children between 1 and 4 years 50%. Twenty-five percent of those who contract the virus in childhood will die due to complications (cirrhosis, liver failure, neoplasia). HBV is responsible for an increased risk (12 to 300 times greater) of developing liver cancer (hepatocarcinoma).
Impact on the population
It is estimated that over 2 million individuals in the world have been infected by HBV, that there are 350-400 million chronic carriers of hepatitis B worldwide, and that one third of the world population carries specific virus antibodies (and who therefore have contracted the virus at some point in their life). Every year 600,000 people die from acute or chronic consequences of HBV infection.
Hepatitis B is endemic in Asia and Eastern Europe: in these regions the prevalence of patients varies from 5% in Russia to over 10% of the adult population in China, where there are about 120,000 people infected and perinatal transmission is the most frequent mode. Other highly endemic countries are India (40 million infected) and Indonesia (12 million). In areas of low prevalence, such as Western Europe and the United States (where there is a prevalence of 0.5%) the pathology is present in particular risk groups (i.e. drug addiction, unprotected sexual relations, occupational exposure and perinatal infection).
In regions of moderate and high prevalence, children have the highest prevalence of HBV infection: the introduction of the vaccine in 1982 has drastically reduced the percentage of HBV-positive children in these countries, from 8% to 1%.
Sources / Bibliography
- Ministero della Salute
- Epidemiology and Prevention of Vaccine-Preventable Diseases, The Pink Book: Course Textbook, 12th Edition Second Printing (May 2012)