Adenovirus Infections Health Article

Definition

Adenoviruses are small infectious agents that cause upper respiratory tract infections, conjunctivitis, and other infections in humans.

Description

Adenoviruses were discovered in 1953. By 2004 about 49 different types had been identified, and about half of those were believed to cause human diseases. Adenovirus infections can occur throughout the year, unlike the seasonality associated with other respiratory viruses.

In children, adenoviruses most often cause acute upper respiratory infections with fever and runny nose. Adenovirus types 1, 2, 3, 5, and 6 are responsible for most of these infections. Occasionally more serious lower respiratory diseases, such as pneumonia or bronchitis, may occur. Adenoviruses can also cause acute diarrhea in young children, characterized by fever and watery stools. This condition is caused by adenovirus types 40 and 41 and can last as long as two weeks.

As much as 51 percent of all hemorrhagic cystitis (inflammation of the bladder and of the tubes that carry urine to the bladder from the kidneys) in American and Japanese children can be attributed to adenovirus infection. A child who has hemorrhagic cystitis has bloody urine for about three days, and invisible traces of blood can be found in the urine a few days longer. The child will feel the urge to urinate frequently but find it difficult to do so, for about the same length of time.

Other illnesses associated with adenovirus include:

• encephalitis (inflammation of the brain) and other infections of the central nervous system (CNS)
• gastroenteritis (inflammation of the stomach and intestines), which sometimes leads to enlarged lymph nodes in the intestines and rarely intussusception
• acute pharyngoconjunctival fever (inflammation of the lining of the eye [conjunctivitis] with fever)
• acute mesenteric lymphadenitis (inflammation of lymph glands in the abdomen)
• chronic interstitial fibrosis (abnormal growth of connective tissue between cells)
• intussusception (a type of intestinal obstruction)
• pneumonia that does not respond to antibiotic therapy
• whooping cough syndrome when Bordetella pertussis (the bacterium that causes classic whooping cough) is not found

Transmission

Specific adenovirus infections can be traced to particular sources and produce distinctive symptoms. In general, however, adenovirus infection is transmitted by the following:

• inhaling airborne viruses
• getting the virus in the eyes by swimming in contaminated water, using contaminated eye solutions or instruments, wiping the eyes with contaminated towels, or rubbing the eyes with contaminated fingers
• not washing the hands after using the bathroom and then touching the mouth or eyes

Infections often occur in situations in which individuals are in close contact with one another, such as the military, cruise ships, or college dormitories. Outbreaks among children are frequently reported at boarding schools and summer camps.

Most children have been infected by at least one adenovirus by the time they reach school age. Most adults have acquired immunity to multiple adenovirus types due to infections they had as children.

Demographics

Adenoviruses are responsible for 3 to 5 percent of acute respiratory infections in children. Most adenovirus infections occur between the ages of six months and five years. The incidence of adenovirus infection does not appear to differ among males and females or individuals of different race.

Causes and symptoms

In one mode of adenovirus infection (called lytic infection because it destroys large numbers of cells), adenoviruses kill healthy cells and replicate up to 1 million new viruses per cell killed, of which 1 to 5 percent are infectious. People with this kind of infection feel sick. In chronic or latent infection, a much smaller number of viruses are released, and healthy cells can multiply more rapidly than they are destroyed. People who have this kind of infection do not exhibit symptoms.

Children who have normal immune systems usually experience only minor symptoms when infected with adenovirus. The course of infection tends to be more serious in children who are immunocompromised, such as those undergoing chemotherapy or those who have a disease that disrupts normal immune response (e.g. human immunodeficiency syndrome [HIV]). In such children, the virus more often affects organs such as the lungs, liver, and kidneys, and the risk of fatality increases.

Symptoms common to respiratory illnesses caused by adenovirus infection include cough, fever, runny nose, sore throat, and watery eyes. In children with gastroenteritis caused by the adenovirus, symptoms may include diarrhea, fever, nausea, vomiting, and respiratory symptoms. Children with acute pharyngoconjunctival fever usually show signs of conjunctivitis, fever, sore throat, runny nose, and inflammation of the lymph glands in the neck (certical adenitis). More rarely, if the virus infects the lining of the brain and spinal cord (meninges) or the brain itself, meningitis or encephalitis may result; symptoms include fever, stiff or painful neck, irritability, changes in personality, or seizures.