The Epidemiology, Transmission, Genotypes, Replication, Serologic and Nucleic Acid Testing, Immunotolerance, and Reactivation of Hepatitis B Virus.

The epidemiology of Hepatitis B virus (HBV) has drastically changed in recent decades due to public health initiatives, including universal infant vaccination programs,urbanization driving global travel, and migration patterns. Despite screening of pregnant women and newborns significantly reducing the rate of perinatal transmission in certain parts of the world, other, perhaps more uncommon, routes (e.g., parenteral) have led to outbreaks in specific areas affected by the opioid epidemic and injection drug use. Although our current understanding of the effect of genetic variants of HBV is lacking, we review current knowledge and patterns of genetic variants with geographical predominance, pathophysiology, and clinical manifestations. Serologic and molecular markers are used to screen, identify phase and activity of infection, and monitor response to antivirals and/or reactivation. This review will provide the most up-to-date summary of the epidemiology, transmission, genotype, replication, and current methods of screening to follow the various phases of HBV, including immunotolerance and reactivation.