Adenoviruses are medium-sized, non-enveloped DNA viruses that primarily infect epithelial tissues in the lungs and intestines. They have an icosahedral protein shell containing DNA and come in two genera - Aviadenovirus which infect birds and Mastadenovirus which infect mammals. Adenoviruses cause respiratory illnesses like pharyngitis, conjunctivitis, and pneumonia as well as gastroenteritis. They are diagnosed through antigen detection, PCR, virus isolation, or serology. Treatment is supportive to relieve symptoms and prevention involves handwashing, disinfection, and chlorination of swimming pools.