Human cytomegalovirus (HCMV or CMV) is a human viral pathogen belonging to the Herpesvirus family found in both the developed industrial societies and in isolated aboriginal groups. It can be transmitted through blood, oropharyngeal secretions, urine, cervical and vaginal excretions, spermatic fluids, breast milk, tears and feces. Primary infections with CMV in immunocompetent individuals are usually asymptomatic and often give rise to undetected latent infections. Peripheral blood mononuclear cells and endothelial cells appear to be the major sites of infection. CMV remains in a latent stage in monocytes/macrophages in humans. Latently infected individuals may intermittently shed the virus in their body fluids and thus infect others. Immunocompromised individuals, including neonates, transplant patients and AIDS patients, are at high risk for developing severe CMV infections that can lead to a higher rate of morbidity and mortality. Severe clinical manifestations of CMV disease include CMV syndrome, retinitis, gastroenteritis, hepatitis, encephalitis, esophagitis, enterocolitis, pancreatitis and pneumonia.