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Adenoviruses cause acute respiratory disease (usually), pneumonia (occasionally), acute follicular conjunctivitis, epidemic keratoconjunctivitis, cystitis, and gastroenteritis (occasionally). In infants, pharyngitis and pharyngeal-conjunctival fever are common.
The icosahedral capsid (70 to 100 nm) is made up of 252 capsomeres: 240 hexons forming the faces and 12 pentons at the vertices. Each penton bears a slender fiber. The double-stranded linear DNA is associated with two major core proteins and carries a 55-kDa protein covalently attached to its 5′ end.
More than 100 antigenic types of adenoviruses have been identified that infect mammals (mastadenoviruses) and birds (aviadenoviruses); 47 human adenovirus types are classified, 5 more candidate types are presently studied.
Infection may be productive, abortive, or latent. In productive infections, the viral genome is transcribed in the nucleus, mRNA is translated in the cytoplasm, and virions self-assemble in the nucleus. In latent infections and in transformed and tumor cells, viral DNA is integrated into the host genome. Virus-host DNA recombinants are also found in productive infections.
Infection is usually transmitted in droplets of respiratory or ocular secretions. Persistent infection occurs in the tonsils. Some adenovirus types are oncogenic in newborn rodents and can transform cells. A few transformed human cell lines exist. Human oncogenesis has not been found but may nevertheless occur (e.g., by a “hit-and-run” mechanism).
Most adolescents and adults have circulating neutralizing antibodies; immunity is widespread. Cytotoxic T lymphocytes destroy adenovirus-infected cells.
Infection is common in children. Epidemics do not occur in the general population, but outbreaks of acute respiratory disease occur in military recruits. Serious complications are very rare.
Adenovirus infection is suggested clinically by fever, upper respiratory tract infections, and conjunctivitis; the diagnosis is confirmed by a rise in antibody titers and by virus isolation.
There is no treatment. Whole-virus vaccines are not used because of the potential risk of oncogenesis. Other vaccines, including recombinant vaccines, are under development, but adenoviruses do not represent a serious health hazard.
Adenoviral genomes have been developed into vectors in experimental therapy since adenoviruses readily infect human and other mammalian cells. Vector genomes carry deletions in the E1 and E3 regions; the gaps in the genome are used to take up foreign genes, e.g., the gene for the cystic fibrosis transmembrane conductance regulator (CFTR). Deletions in E1 minimize the potential of these vector genomes to elicit an infection cycle in human cells. The first clinical applications in patients suffering from the genetic disease cystic fibrosis have been reported but problems with adenovirus toxicity remain.
