Adenoviruses are respiratory pathogens, widespread in nature, infecting birds (aviadenoviruses) and many mammals including man (mastadenoviruses). They are highly species-specific. They can can infect the membranes (tissue linings) of the respiratory tract, the eyes, the intestines and urinary tract. Infections can range from asymptomatic to fatal.
In humans, adenoviral infections are a frequent cause of acute upper respiratory tract (URT) infections, i.e. "colds". In addition, they also cause a number of other types of infection including pharyngitis, pneumonia, gastroenteritis, conjunctivitis ("pink-eye") and keratoconjunctivitis in infants and young people, and more rarely acute haemorrhagic cystitis and hepatitis, mainly in infants or in the latter case those with liver disease.
Adenoviruses were first isolated in 1953 by investigators trying to establish cell-lines from adenoidal tissue of children removed during tonsillectomy and from military recruits with febrile illness. In 1962, some adenoviruses were shown to cause tumours in rodents but this has never been observed in humans.
Adenovirus infections are very common, most are asymptomatic. Most people have been infected with at least one type by age 15. Virus can be isolated from the majority of tonsils/adenoids surgically removed, indicating latent infections. It is not known how long the virus can persist in the body, or whether it is capable of reactivation after long periods, causing disease It is known that virus is reactivated during immunosuppression, e.g. in AIDS patients.
5% of acute respiratory disease in children under 5 years of age is caused by adenoviruses and 10% of the pneumonias. Adenoviral infections are difficult to distinguish from influenza, parainfluenza and RSV. Conjunctivitis can occur with respiratory illness in such cases the disease is called pharyngoconjunctival fever.
Acute respiratory disease (ARD) is commonly seen in military recruits probably due to fatigue and crowding in barracks. Two types of adenovirus (known as 4 and 7) are responsible for these outbreaks and a vaccine is available.
Eye infections characterized by a mild conjunctivitis "swimming pool conjunctivitis" are caused by adenoviruses and have been linked to transmission in contaminated swimming pools.
Adenoviral types 8 and 37 can cause a more severe illness known as epidemic keratoconjunctivitis (EKC). Corneal opacity with concomitant vision loss in 10% of cases.