Protein–protein interactions (PPIs) are fundamental to viral replication, regulating processes such as assembly, genome packaging, and virion maturation. Despite their biological importance, these interactions remain challenging to study and are relatively underexploited as therapeutic targets. Split reporter systems, based on protein-fragment complementation, provide quantitative platforms to measure PPIs by reconstituting reporter activity when interacting protein partners are brought into proximity. These systems can be applied in vitro and in live cells which enables detection of dynamic and multimeric interactions in physiologically relevant contexts. Major classes of split reporter systems include β-lactamase, alkaline phosphatase, luciferase-based platforms, green fluorescent protein, and horseradish peroxidase. Assay performance depends on factors such as fusion protein stability, expression levels, and reporter kinetics, which influence sensitivity, dynamic range, and reliability. These approaches have been applied to study viral protein interactions across diverse systems, including HIV-1 matrix and nucleocapsid proteins, flaviviral capsid proteins, hepatitis B virus core protein, and chikungunya virus capsid. Split reporter assays also enable high-throughput screening for small-molecule inhibitors that disrupt viral PPIs and multimerization. This provides a functional readout linked to viral replication. Despite the challenges that exist in assay optimization and protein stability, the sensitivity and versatility of these systems provide a framework to interrogate viral protein interactions and support the development of antiviral therapeutics.:

Hepatitis B virus (HBV) infection is a worldwide health concern that infects nearly 254 million people globally and causes more than 1 million deaths annually. The highest prevalence is seen in sub-Saharan Africa and the Western Pacific region. Cirrhosis, liver failure, and hepatocellular carcinoma (HCC) are reported as leading complications of chronic HBV. The route of transmission of this infection is mainly by exposure to infected blood and bodily fluids. Transmission from mother-to-child remains the predominant route in highly endemic areas. Vaccination has significantly reduced HBV seroprevalence and complications. However, incomplete vaccination of newborns continues to be a major obstacle to elimination of the disease. Current prevention strategies include universal vaccination, perinatal prophylaxis with hepatitis B immune globulin, and maternal antiviral therapy in pregnant women with high viral load. The management of chronic hepatitis B virus infection predominantly depends on nucleoside analogs, including entecavir, tenofovir disoproxil fumarate, and tenofovir alafenamide, as well as pegylated interferon alfa. These therapies effectively suppress viral replication and reduce the risks of cirrhosis, HCC, and liver-related mortality, but they rarely achieve functional cure characterized by hepatitis B surface antigen loss. The persistence of covalently closed circular DNA (cccDNA) remains a major hindrance in HBV eradication. Therefore, novel therapeutic strategies targeting different stages of the viral life cycle, including capsid assembly modulators, small interfering RNAs, nucleic acid polymers, and cccDNA-directed approaches, are under active investigation. This review summarizes the epidemiology, prevention, current therapies, clinical outcomes, and emerging therapeutic advances in HBV infection, highlighting ongoing efforts toward achieving a functional cure and global HBV elimination.