ADENOVIRUSES

Adenoviruses are a group of virus that cause infection in tissue lining - mostly the membranes of the respiratory tract, and they are a frequent cause of acute upper respiratory tract infections; otherwise known as colds. They also infect the tissues of other parts of the body, including eyes, intestines, and the urinary tract. Besides colds, they can also cause gastroenteritis (stomachache and diarrhea), conjunctivitis (eye infections, cystitis (bladder or urinary tract infections) and rashes. Respiratory illnesses caused by adenoviruses can range from colds to more serious infections such as pneumonia, croup, and bronchitis.

Most people will have experienced at least one infection caused by adenoviruses before the age of 10. In fact, children and infants are more succeptible to adenovirus infections than healthy adults.

Patients with compromised immune systems are also especially susceptible to severe complications of adenovirus infection. Acute respiratory disease (ARD), which was first recognized among military recruits during World War II, can be caused by adenovirus infections during conditions of crowding and stress.

Adenoviruses: The Viruses Themselves

Adenoviruses are type of viruses, and they are classified by their shape and their doublestranded DNA. There are 49 immunologically distinct types of adenoviruses, with six subtypes, that can cause infections in people.

Adenoviruses are particularly hardy viruses, and they can survive for long periods of time outside a host (or people who carry the virus), which means that they are typically very contagious.

Transmission of Adenoviruses and Types of Infection

Although the ways adenoviruses can be spread vary depending on their type, all adenoviruses can be spread by direct contact, fecal-oral transmission, and occasionally waterborne transmission.

Some types are capable of living inside a person or a host's tonsils, adenoids, and intestines for months or years without showing any symptoms of infection. Some adenoviruses (e.g., serotypes 1, 2, 5, and 6) have been shown to be endemic or widespread to certain countries, and infection usually happens during childhood.

Other types cause sporadic infection and occasional outbreaks; for example, epidemic keratoconjunctivitis (a severe type of eye infection) is associated with three types of adenoviruses - adenovirus serotypes 8, 19, and 37. Epidemics of febrile disease (respiratory tract infections that cause a fever) with conjunctivitis often can be contracted through waterborne transmission - the adenoviruses can sometimes be found in inadequately chlorinated swimming pools and small lakes.

In the United States, ARD is most often associated with two types of adenoviruses, types 4 and 7. Two other types of adenoviruses, types 40 and 41, are often found to cause gastroenteritis, usually in children. For some types of adenovirus, the kinds of infection they cause depend on where a person gets the infection. For example, people who are infected by adenovirus 7 through inhaling it, suffer severe lower respiratory tract disease, whereas if they had received the virus via oral transmission, this type of transmission typically causes mild symptoms or none at all. Outbreaks of adenovirus-associated respiratory disease are more common in the late winter, spring, and early summer, but they can occur at any time of the year.

Treatment, Diagnosis and Prevention

There are several technologies that can be used to determine if someone is infected with an adenovirus and what sort of adenovirus is causing the infection. Usually, a doctor will swap or take tissue samples of the infected areas, and then a laboratory uses several tests to identify the cause of infection. But because adenoviruses can be in a host for a long period of time, the presence of virus does not necessarily mean it is associated with disease.

Most infections caused by adenoviruses are mild and require no therapy or only symptomatic treatment. Because there is no virus-specific therapy, serious adenovirus illness can be managed only by treating symptoms and complications of the infection.

Vaccines have been developed for two types of adenoviruses - adenovirus serotypes 4 and 7 — and they have been used to prevent ARD among military recruits. But the best way to prevent adenoviruses is good infection-control practices. These preacticies include maintaining adequate levels of chlorination is necessary for preventing swimming pool-associated outbreaks of adenovirus conjunctivitis.