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Hepatitis B is an infectious disease caused by the hepatitis B virus (HBV) which affects the liver. It can cause both acute and chronic infections. Many people have no symptoms during the initial infection. Some develop a rapid onset of sickness with vomiting, yellowish skin, feeling tired, dark urine and abdominal pain.〔 Often these symptoms last a few weeks and rarely does the initial infection result in death.〔 It may take 30 to 180 days for symptoms to begin.〔 In those who get infected around the time of birth 90% develop chronic while less than 10% of those infected after the age of five do.〔 Most of those with chronic disease have no symptoms; however, cirrhosis and liver cancer may eventually develop. These complications result in the death of 15 to 25% of those with chronic disease.〔 The virus is transmitted by exposure to infectious blood or body fluids. Infection around the time of birth or from contact with other people's blood during childhood is the most frequent method by which hepatitis B is acquired in areas where the disease is common. In areas where the disease is rare, intravenous drug use and sexual intercourse are the most frequent routes of infection.〔 Other risk factors include working in healthcare, blood transfusions, dialysis, living with an infected person, travel in countries where the infection rate is high, and living in an institution.〔〔(【引用サイトリンク】url=http://www.cdc.gov/hepatitis/B/bFAQ.htm#transmission )〕 Tattooing and acupuncture led to a significant number of cases in the 1980s; however, this has become less common with improved sterility. The viruses cannot be spread by holding hands, sharing eating utensils, kissing, hugging, coughing, sneezing, or breastfeeding.〔 The infection can be diagnosed 30 to 60 days after exposure. Diagnosis is typically by testing the blood for parts of the virus and for antibodies against the virus.〔 It is one of five known hepatitis viruses: A, B, C, D, and E. The infection has been preventable by vaccination since 1982.〔 Vaccination is recommended by the World Health Organization in the first day of life if possible. Two or three more doses are required at a later time for full effect. This vaccine works about 95% of the time.〔 About 180 countries gave the vaccine as part of national programs as of 2006. It is also recommended that all blood be tested for hepatitis B before transfusion and condoms be used to prevent infection. During an initial infection, care is based on the symptoms that a person has. In those who develop chronic disease antiviral medication such as tenofovir or interferon maybe useful, however these drugs are expensive. Liver transplantation is sometimes used for cirrhosis.〔 About a third of the world population has been infected at one point in their lives, including 240 million to 350 million who have chronic infections.〔 Over 750,000 people die of hepatitis B each year. About 300,000 of these are due to liver cancer. The disease is now only common in East Asia and sub-Saharan Africa where between 5 and 10% of adults have chronic disease. Rates in Europe and North America are less than 1%.〔 It was originally known as serum hepatitis. Research is looking to create foods that contain HBV vaccine. The disease may affect other great apes as well. ==Signs and symptoms== Acute infection with virus is associated with acute viral hepatitis – an illness that begins with general ill-health, loss of appetite, nausea, vomiting, body aches, mild fever, and dark urine, and then progresses to development of jaundice. It has been noted that itchy skin has been an indication as a possible symptom of all hepatitis virus types. The illness lasts for a few weeks and then gradually improves in most affected people. A few people may have more severe liver disease (fulminant hepatic failure), and may die as a result. The infection may be entirely asymptomatic and may go unrecognized. Chronic infection with virus either may be asymptomatic or may be associated with a chronic inflammation of the liver (chronic hepatitis), leading to cirrhosis over a period of several years. This type of infection dramatically increases the incidence of hepatocellular carcinoma (liver cancer). Across Europe hepatitis B and C cause approximately 50% of hepatocellular carcinomas. Chronic carriers are encouraged to avoid consuming alcohol as it increases their risk for cirrhosis and liver cancer. virus has been linked to the development of membranous glomerulonephritis (MGN). Symptoms outside of the liver are present in 1–10% of HBV-infected people and include serum-sickness–like syndrome, acute necrotizing vasculitis (polyarteritis nodosa), membranous glomerulonephritis, and papular acrodermatitis of childhood (Gianotti–Crosti syndrome). The serum-sickness–like syndrome occurs in the setting of acute , often preceding the onset of jaundice. The clinical features are fever, skin rash, and polyarteritis. The symptoms often subside shortly after the onset of jaundice, but can persist throughout the duration of acute . About 30–50% of people with acute necrotizing vasculitis (polyarteritis nodosa) are HBV carriers. HBV-associated nephropathy has been described in adults but is more common in children. Membranous glomerulonephritis is the most common form.〔 Other immune-mediated hematological disorders, such as essential mixed cryoglobulinemia and aplastic anemia.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hepatitis B」の詳細全文を読む スポンサード リンク
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