Occult hepatitis B: prevalence and clinical significance. Role in liver pathology and in viral coinfections.

The review examines issues related to occult hepatitis B virus infection (OBI), which occurs at a late stage of chronic hepatitis B (CHB) after HBsAg clearance. In clinical practice, OBI is detected by the absence of HBsAg and the presence of antibodies to HBcAg in the blood serum and is often referred to as «past» or «resolved» hepatitis B. However, hepatitis B virus (HBV) DNA remains in liver cells, is poorly detected by routine diagnostic methods, and cannot be removed by existing therapies. Data on the prevalence of OBI vary, but it is found in all regions of the world, much more often in regions with a high prevalence of HBV. Data on the association of OBI with fibrosis, cirrhosis and hepatocellular carcinoma (HCC) have been obtained. It has been established that OBI is associated with an increased risk of HBV reactivation in patients with infections with other viruses, as well as in cancer patients whose treatment includes immunosuppressive therapy. HBV reactivation leads to severe consequences and, in the absence of treatment, death of patients. It can be concluded that to achieve the goal set by WHO for the eradication of viral hepatitis by 2030, it is necessary to solve the problem of OBI. In order to make this possible, it is essential to create new, more sensitive and informative diagnostic tests, effective methods of HBV DNA elimination, and to investigate the mechanisms of OBI development in more depth.