Wild-Type Human Adenovirus (Serotype 25)

Wild-type human adenovirus 25 (Ad25) is a non-enveloped, double-stranded DNA virus belonging to the human papillomavirus (HPV) species D. It is primarily transmitted through respiratory droplets, the fecal-oral route, and contaminated objects. Ad25 exhibits tropism for epithelial cells in respiratory, digestive, and ocular tissues. After entering cells via the Coxsackievirus and adenovirus receptors (CAR) or CD46, the virus initiates infection through endocytosis and endosome escape. The virus replicates within the cell nucleus, leading to cytopathic effects and cell lysis. Its pathogenic mechanisms involve both direct tissue damage and inflammation-mediated damage. Ad25 is associated with conjunctivitis, gastroenteritis, and respiratory illnesses, particularly in immunocompromised individuals and young children. The virus can establish persistent infection in lymphoid tissues and may evade immune surveillance via immunomodulatory proteins in the E3 region.

Ad25 possesses a characteristic icosahedral capsid, approximately 90 nm in diameter, composed of a complex of 240 hexagonal trimers and 12 pentameric bases. Each pentazocine base anchors a fibrin, which determines serotype specificity and host cell binding. Ad25''s fibrin globular domain binds to the host receptor, while the pentazocine bases interact with integrins, triggering clathrin-mediated endocytosis. The Ad25 genome contains a linear double-stranded DNA molecule of approximately 36 kilobase pairs (kbp). The genome has inverted terminal repeats (ITRs) at both ends, serving as origins of replication and packaging signals. It encodes approximately 40 genes organized into early (E1-E4), mid-terminal, and late (L1-L5) transcriptional units. Early genes regulate the host cell cycle and immune escape (e.g., E1A antagonizes the interferon response), while late genes produce structural proteins such as hexazine, pentazine, and fibrin. The genome also contains virus-associated RNA (VA RNA), which suppresses host RNA interference.