|Transmission Electron Micrograph (TEM) of adenovirus particles. Adenoviruses (members of the family Adenoviridae) are non-enveloped viruses with an icosahedral nucleocapsid containing a double stranded DNA genome. Adenovirus infections most commonly cause illness of the respiratory system, however, depending on the infecting serotype, they may also cause various other illnesses and presentations. Apart from respiratory involvement, illnesses and presentations of adenovirus include gastroenteritis, conjunctivitis, cystitis, and rash illness. Symptoms of respiratory illness caused by adenovirus infection range from the common cold syndrome to pneumonia, croup, and bronchitis. Patients with compromised immune systems are especially susceptible to severe complications of adenovirus infection.