Soon after HBV enters the body, it infects cells in the liver called hepatocytes. In response to this infection, the immune system targets the virus and targets the hepatocytes already infected with the virus. This causes inflammation of the liver (hepatitis).
HBV can cause acute hepatitis, meaning short-term inflammation of the liver, until the immune system is able to clear the virus from the body, usually within six months of becoming infected with the virus. However, HBV can become a chronic infection. This means that the immune system is not able to get rid of the virus within six months after infection. In other words, the virus continues to reproduce in the person's liver for several months or years after infection. This can increase the risk of liver damage and liver cancer. What's more, someone with chronic HBV infection can transmit the virus to others.
Less than 10% of adults infected with HBV go on to experience chronic HBV infection. Babies infected with HBV around the time of birth go on to experience chronic HBV infection approximately 90% of the time, which is why it is important that pregnant women know whether or not they are infected with the virus before giving birth. Medication can be given to the baby after birth to help prevent hepatitis B. Young children who are infected with HBV have a 25% to 50% risk of developing chronic hepatitis B. With adults, the risk of developing chronic HBV infection depends on the health of the immune system. For example, patients with impaired immune responses who are recovering from organ transplants, undergoing chemotherapy, undergoing dialysis for kidney problems, receiving steroid therapy to suppress the immune system, or are HIV-positive are more likely to develop chronic HBV infection than patients with normal immune responses. In other words, HIV-positive people are more likely to develop chronic HBV infection after being infected with the virus than HIV-negative people (with healthy immune systems).
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