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Cytomegalovirus (CMV) (from the Greek cyto-, "cell", and -mega-, "large") is a viral genus of the Herpesviruses group: in humans it is commonly known as human herpesvirus 5 (HHV-5). CMV belongs to the Betaherpesvirinae subfamily of Herpesviridae, which also includes Roseolovirus, also known as Human Herpes Virus 6 (HHV-6). The Alphaherpesvirinae contains herpes simplex virus types 1 and 2, and varicella-zoster virus (which causes chickenpox and shingles). The Epstein-Barr virus belongs to the Gammaherpesvirinae subfamily. The herpesviruses share a characteristic ability to remain latent within the body over long periods. CMV infections are frequently associated with salivary glands, though they may be found throughout the body. CMV infection can also be life threatening for patients who are immunocompromised (e.g. patients with HIV, organ transplant recipients, or neonates).[1] CMV viruses are found in many mammal species, but CMV species isolated from animals differ from human CMV in terms of genomic structure, and have not been reported to cause human disease. In humans, CMV is found throughout all geographic locations and socioeconomic groups, and infects between 50% and 80% of adults in the United States as indicated by the presence of antibodies in much of the general population. CMV is also the virus most frequently transmitted to a developing child before birth. CMV infection is more widespread in developing countries and in areas of lower socioeconomic conditions and causes the most birth defects in industrialized countries of all the herpes viruses. Species
Pathogenesis
For most healthy individuals who acquire CMV after birth there are few symptoms.[1] Some persons with symptoms experience an infectious mononucleosis-like syndrome , with prolonged fever, and a mild hepatitis. A very sore throat is also common. Once a person becomes infected, the virus latently persists in the body for the person's life and can exhaust the immune system at old age, increasing risk of mortality from other diseases. Recurrent disease rarely occurs unless the person's immune system is suppressed due to therapeutic drugs or disease. 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. CMV infection is important to certain high-risk groups. Major areas of risk of infection include pre-natal or post-partum infants and immunocompromised individuals, such as organ transplant recipients, persons with leukemia, or those infected with human immunodeficiency virus (HIV). CMV is considered an AIDS-defining infection, indicating that the T-cell count has dropped to low levels. Lytically replicating virus disrupts the cytoskeleton, causing massive cell enlargement, which is the source of the virus' name.
Transmission and prevention Transmission of CMV occurs from person to person. Seroprevalence is age-dependent: 58.9% of individuals aged 6 and over are infected with CMV while 90.8% of individuals aged 80 and over are positive for CMV. 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 CMV is not highly contagious, it has been shown to spread in households and among young children in day care centers.[1] 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.
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