Human adenovirus 2 is a non‑enveloped, double‑stranded DNA virus of species C in the genus Mastadenovirus. Its virion consists of a sturdy icosahedral capsid with 252 capsomeres and a linear genome linked to terminal proteins. Type 2 is a common cause of mild respiratory illness, particularly in young children, and like other adenoviruses it replicates in epithelial cells of the nasopharynx and conjunctiva.
Biology and pathogenesis
Adenoviruses as a group have over a hundred antigenically distinct types grouped into species A through G. The virions are 70–90 nm particles whose double‑stranded DNA genome replicates in the host cell nucleus. HAdV‑2, along with types 1 and 5, belongs to species C and is transmitted in respiratory droplets or by contaminated fomites. After entering the upper respiratory tract it infects epithelial cells, leading to lytic replication and shedding of infectious particles. Infections may be productive, abortive or latent depending on the cell type. The virus can persist in lymphoid tissues such as the tonsils and adenoids. Host defence against adenovirus infection relies on neutralising antibodies and cytotoxic T cells, and by age five most individuals have serologic evidence of infection.
Clinical features and notable facts
HAdV‑2 infection usually manifests as self‑limited fever, cough, nasal congestion and pharyngitis. Conjunctival involvement may lead to pharyngoconjunctival fever, especially in outbreaks linked to swimming pools or summer camps. Type 2 is less likely than types 7, 14 or 21 to cause severe pneumonia, but it can occasionally lead to bronchiolitis or otitis media in infants. Unlike types 8, 19 or 37 that cause epidemic keratoconjunctivitis, or enteric types 40/41 that cause paediatric gastroenteritis, HAdV‑2 is primarily a respiratory pathogen. Its ability to infect both dividing and non‑dividing cells has made it a useful backbone for gene therapy vectors and vaccine delivery systems, although such uses involve replication‑defective derivatives rather than wild‑type virus. Human adenovirus 2 is ubiquitous and establishes early‑life immunity in most populations. Natural infection is generally mild and confers type‑specific antibody responses, but immunocompromised hosts may experience prolonged shedding. Its combination of respiratory tropism and well‑characterised genome has also made it a workhorse in virology research. Related Terms: Human Adenovirus 1, Human Adenovirus 5, Adenovirus vector, Pharyngoconjunctival fever