Microorganism: the hepatitis B virus is a member of the family Hepadnaviridae.

Disease: hepatitis B

Occurrence of the disease

Current situation: In 1998, 970 cases of hepatitis B were reported in Canada. In industrialized countries, persons most susceptible to this virus are those who use contaminated needles for injecting intravenous drugs. Throughout the world, 200 million people suffer from a chronic infection caused by the hepatitis B virus.

Mechanism of action of the microorganism: the microorganism enters the blood and infects the hepatic cells, that is, the cells of the liver. The infection can cause the breakdown of certain blood components, which can result in jaundice.

Symptoms of the disease: most persons infected with the hepatitis B virus show no symptoms during the first six weeks, or even up to six months, following infection. After a certain period, the disease gradually becomes apparent through fever, loss of appetite, abdominal pain, nausea, and fatigue. There is often jaundice, a condition in which the skin becomes yellow. The disease is generally not fatal; nevertheless, in five to ten per cent of cases, the virus persists in the host for many years. A chronic, or long-term, infection may eventually cause liver cancer, or hepatocellular carcinoma. This type of cancer, while rare in the United States, is more common in certain regions of Africa and south Asia.

Incubation period: 60 to 90 days, on average

Contagious period: the contagious period begins several weeks before the appearance of symptoms and continues during the acute phase of the disease.

Hosts: humans

Transmission: through contaminated blood products or through sexual contact. The virus can also be transmitted from a mother to her baby.

Transmission by means of blood transfusion is now rare in industrialized countries, since blood is systematically tested for the presence of the hepatitis B virus at the time of donation.

Treatment: a person who believes that he or she has been in contact with contaminated blood may receive an injection of anti-hepatitis antibodies (immunoglobulins) within the next seven days.

Geographical distribution of the microorganism: worldwide

Prevention: vaccine. Use of condoms is another means of prevention, as is limiting the number of sexual partners. Good hygiene in other respects is advised, that is, regular hand washing, especially following contact with blood. Finally, one should avoid sharing syringes, razors, and even toothbrushes.

Vaccine: the vaccine against hepatitis B was the first human vaccine developed through recombinant DNA technology. This vaccine consists of a part of the virus called the surface antigen. In Quebec, elementary school children in fourth grade, as well as women with high-risk behavior, are vaccinated against hepatitis B.

Side-effects of the vaccine: in most cases, the vaccine has no side-effects. Nevertheless, some people may have redness or slight swelling at the site of the injection. Very rarely, the vaccine can cause headaches, fever, muscle pain and allergic reactions. The vaccine is effective in 90% of cases.


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