Adenoviruses

There are a total of 41 types of adenoviruses and they cause a wide variety of diseases. Influenza infections of the upper, less frequently the lower, respiratory tract and eye infections (follicular conjunctivitis, keratoconjunc­tivitis) are among the more significant clinical pictures. Intestinal infections are mainly caused by the only not culturable virus types 40 and 41. Diagnosis: antibody assay in respiratory adenovirus infections. Serology is not reliable in the eye and intestinal infections. It is possible to isolate the pathogens in cell cultures from eye infections. Enteral adenoviruses are detected in stool by means of electron microscopy, enzyme immunoassay, or passive agglutina­tion.

Pathogens. Adenoviruses are nonenveloped, 70-90 nm in size, and icosahedral. Their morphogenesis occurs in the cell nucleus, where they also aggre­gate to form large crystals (Fig. 1). Their genome is a linear, 36-38 kbp dou­ble-stranded DNA. Adenoviruses got their name from the adenoidal tissues (tonsils) in which they were first identified.

Pathogenesis and clinical picture. Adenoviruses cause a variety of diseases, which may occur singly or concurrently. The most important are infections of the upper (sometimes lower) respiratory tracts, the eyes, and the intestinal tract.

-Infections of the respiratory tract take the form of rhinitis or abacterial pharyngitis, depending on the virus type as well as presumably on the dis­position of the patient. They may also develop into acute, influenzalike infec­tions or even, especially in smallchildren, into a potentially fatal pneumonia.

-The eye infections, which may occur alone but are often concurrent with pharyngitis, range from follicular conjunctivitis to a form of keratoconjunc­tivitis that may even cause permanent partial loss of eyesight.

Fig. 1 Viral crystals in the nucleus of the host cell (TEM(.

-An important aspect of the intestinal infections is that the primary gas­troenteritis forms are caused by the viral strains 40 and 41, which are difficult to culture.

Adenoviruses can persist for months in the regional lymph nodes or tonsils until they are reactivated.

Diagnosis. Antibody assays in patient serum are the main approach taken in respiratory adenovirus infections. Serology is unreliable in the eye and intes­tinal infections, since hardly any antibodies are produced in response to such highly localized infections. It is possible to isolate the viruses that cause re­spiratory infections by inoculating cell cultures with pharyngeal material or bronchial secretion and with conjunctival smears in eye infections. Enteral adenoviruses, on the other hand, are hard to culture. The best approach to detecting them is therefore to subject stool specimens to electron micro­scopy, enzyme immunoassay, or passive agglutination methods.

Epidemiology and prevention. Humans are the source of infection. Suscep­tibility is the rule. Generalized contamination of the population begins so early in childhood that adenovirus infections play a more significant role in children than in adults. Transmission of respiratory adenoviruses is pri­marily by droplet infection, but also as smear infections since the virus is also excreted in stool. Eye infections can be contracted from bathing water or, in the case of adenovirus type 8 in particular, iatrogenically from insufficiently sterilized ophthalmological instruments. The enteral infections are also transmitted by the fecal-oral route, mainly by contact rather than in water or food. Adenoviruses are the second most frequent diarrhea pathogen in children after rotaviruses.