乙型肝炎病毒
乙型肝炎病毒（Hepatitis B ）是引起乙型肝炎（简称乙肝）的病原体，属嗜肝DNA病毒科，该科病毒包含正嗜肝DNA病毒属和禽嗜肝DNA病毒属两个属，引起人体感染的是正嗜肝DNA病毒属。HBV感染是全球性的公共卫生问题，随着基因工程疫苗的生产和投入，乙肝疫苗的普及率逐年上升，感染率呈下降趋势。
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The Hepatitis B virus (HBV) is the causative agent of Hepatitis B (often referred to simply as Hep B). It belongs to the Hepadnaviridae family of liver-loving DNA viruses, which comprises two genera: the Orthohepadnavirus and the Avihepadnavirus. The one responsible for human infection is the Orthohepadnavirus. HBV infection is a global public health issue. With the production and implementation of genetically engineered vaccines, the prevalence of Hepatitis B vaccinations has been increasing yearly, leading to a decline in infection rates.
Biological Characteristics:
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Morphology and Structure: Under an electron microscope, the Hepatitis B virus presents three types of particle structures: large spherical particles of about 42nm in diameter, small spherical particles of about 22nm, and tubular particles. The large spherical particle (known as Dane particle) is the complete virus particle, comprising an envelope and a nucleocapsid. The envelope contains HBsAg, glycoproteins, and cellular lipids, while the core particle contains the core protein (HBcAg), circular double-stranded HBV-DNA, and HBV-DNA polymerase. This represents the complete form of the virus and is infectious. Both the small spherical and tubular particles consist of lipoproteins identical to the viral envelope. The former is mainly formed from HBsAg into hollow particles, lacking DNA and DNA polymerase, and is non-infectious. The latter consists of small spherical particles chained together, with components identical to the small spherical particles.
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Viral Life Cycle: HBV adheres to the surface of liver cells through low-affinity receptors, such as heparan sulfate and proteoglycans. It then internalizes via the binding of the preS1 region of the large envelope protein to the virus receptor, mediating cellular endocytosis of the virus. The Sodium Taurocholate Co-transporting Polypeptide (NTCP) is a crucial receptor that mediates HBV entry into cells and establishes infection. Once inside, the viral envelope fuses with the endosome, releasing the nucleocapsid into the cytoplasm, which is then transported to the nuclear pore complex, releasing its rcDNA into the cell nucleus. Within the nucleus, rcDNA may be converted into covalently closed circular DNA (cccDNA) through the cell's DNA replication mechanisms. cccDNA is highly stable and can persist in the nucleus for months to years. This persistence is a fundamental reason for viral relapse after antiviral treatment, making the elimination of cccDNA crucial for curing Hepatitis B. The virus transcribes 3.5kb, 2.4kb, 2.1kb, and approximately 0.8kb mRNAs from cccDNA. Among these, the 3.5kb is the pre-genomic RNA (pgRNA), which is reverse transcribed into genomic DNA and serves as the template for the synthesis of the viral core protein and polymerase protein. After HBsAg synthesis, it polymerizes in the rough endoplasmic reticulum and is then transported to the Golgi apparatus to package the core particle. The assembled HBV particles and subviral particles are transported to the Golgi for HBsAg glycosylation modification. Finally, mature virus particles are secreted from the host cell through budding, completing their life cycle.
It is a virus that can potentially lead to cancer.
乙型肝炎病毒（Hepatitis B ）是引起乙型肝炎（简称乙肝）的病原体，属嗜肝DNA病毒科，该科病毒包含正嗜肝DNA病毒属和禽嗜肝DNA病毒属两个属，引起人体感染的是正嗜肝DNA病毒属。HBV感染是全球性的公共卫生问题，随着基因工程疫苗的生产和投入，乙肝疫苗的普及率逐年上升，感染率呈下降趋势。
生物学特征
1.形态和结构
乙肝病毒在电子显微镜下可呈3种形态的颗粒结构：直径约42nm的大球形颗粒、直径约22nm的小球形颗粒以及管型颗粒。大球形颗粒（Dane 颗粒）为完整的病毒颗粒，由包膜和核衣壳组成，包膜含HBsAg、糖蛋白和细胞脂肪，核心颗粒内含核心蛋白（HBcAg）、环状双股HBV-DNA和HBV-DNA多聚酶，是病毒的完整形态，有感染性。小球形颗粒以及管型颗粒均由与病毒包膜相同的脂蛋白组成，前者主要由HBsAg形成中空颗粒，不含DNA和DNA多聚酶，不具传染性；后者是小球形颗粒串联聚合而成，成分与小球形颗粒相同。
2.病毒生活周期
HBV通过低亲和力受体（如硫酸乙酰肝素、蛋白多糖等），黏附到肝细胞表面，再通过大包膜蛋白的preS1区与病毒受体结合介导细胞对病毒的内吞作用。钠离子-牛磺胆酸供转运多肽（NTCP）是介导HBV进入细胞和建立感染的重要受体，在内吞体病毒包膜和吞体膜融合将衣壳释放入细胞质，衣壳被运送至核孔复合体，内部的病毒基因组rcDNA释放入细胞核。在细胞核内，rcDNA可能通过细胞的DNA复制机制转化成共价闭合环状DNA（cccDNA）。cccDNA有高度的稳定性，在细胞核内可以维持数月至数年，这是抗病毒治疗结束后病毒反弹的根本原因，因此清除cccDNA对根治乙型肝炎具有决定性意义。病毒利用cccDNA转录出3.5kb，2.4kb，2.1kb及约0.8kb的mRNA，其中3.5kb为前基因组RNA（pgRNA），可反转录出基因组DNA并作为编码病毒核心蛋白和聚合酶蛋白的模板，HBsAg合成后在粗面内质网中多聚化，并转运至高尔基体前腔以包装核心颗粒，装配好的HBV颗粒与亚病毒颗粒转运至高尔基体进行HBsAg的糖基化修饰，最后以出芽方式将完整的病毒粒子分泌出宿主细胞而完成生活周期。
它是一种可能导致癌症的病毒。