Cytomegalovirus

Initial CMV infection, which may have few symptoms, is always followed by a prolonged, inapparent infection during which the virus resides in cells without causing detectable damage or clinical illness. Severe impairment of the body's immune system by medication or disease (see below) may reactivate the virus from the latent or dormant state.

Infectious CMV may be shed in the bodily fluids of any previously infected person, and thus may be found in urine, saliva, blood, tears, semen, and breast milk. The shedding of virus may take place intermittently, without any detectable signs, and without causing symptoms.

Microscopically, CMV can be demonstrated by intranuclear inclusion bodies, which show that the virus replicates in the nucleus rather than the cytosol. These inclusion bodies stain dark pink on an H&E stain, and are also called "Owl's Eye" inclusion bodies.

As a result of efforts to create an attenuated-virus vaccine, there currently exist two general classes of CMV. Clinical isolates comprise those viruses obtained from patients and represent the wild-type viral genome, while laboratory strains have been cultured extensively in the lab setting and typically contain numerous accumulated mutations. Most notably, the laboratory strain AD169 appears to lack a 15kb region of the 200kb genome that is present in clinical isolates. This region contains 19 open reading frames whose functions have yet to be elucidated. AD169 is also unique in that it is unable to enter latency and nearly always assumes lytic growth upon infection. Transmission of CMV occurs from person to person. 58.9% of individuals aged 6 and over are infected with CMV; this number rises to 90.8% of individuals aged 80 and over.[1] It is debatable whether any measures to prevent infection should be taken at all when dealing with someone with CMV, as infection is almost universal in all countries.

Infection requires close, intimate contact with a person excreting the virus in their saliva, urine, or other bodily fluids. CMV can be sexually transmitted and can also be transmitted via breast milk, transplanted organs, and rarely from blood transfusions.

Although the virus is not highly contagious, it has been shown to spread in households and among young children in day care centers. Transmission of the virus is often preventable because it is most often transmitted through infected bodily fluids that come in contact with hands and then are absorbed through the nose or mouth of a susceptible person. Therefore, care should be taken when handling children and items like diapers. Simple hand washing with soap and water is effective in removing the virus from the hands.

CMV infection without symptoms is common in infants and young children; as a result, it is common to not exclude from school or an institution a child known to be infected. Similarly, hospitalized patients are not typically separated or isolated.

Most healthy people working with infants and children face no special risk from CMV infection. However, for women of child-bearing age who previously have not been infected with CMV, there is a potential risk to the developing unborn child (the risk is described above in the Pregnancy section). Contact with children who are in day care, where CMV infection is commonly transmitted among young children (particularly toddlers), may be a source of exposure to CMV. Since CMV is transmitted through contact with infected body fluids, including urine and saliva, child care providers (meaning day care workers, special education teachers, therapists, as well as mothers) should be educated about the risks of CMV infection and the precautions they can take. Day care workers appear to be at a greater risk than hospital and other health care providers, and this may be due in part to the increased emphasis on personal hygiene in the health care setting.

Recommendations for individuals providing care for infants and children:

    * Female employees should be educated concerning CMV, its transmission, and hygienic practices, such as handwashing, which minimize the risk of infection.
    * Susceptible nonpregnant women working with infants and children should not routinely be transferred to other work situations.
    * Pregnant women working with infants and children should be informed of the risk of acquiring CMV infection and the possible effects on the unborn child.
    * Routine laboratory testing for CMV antibody in female workers is not recommended, but can be performed to determine their immune status