Cytomegalovirus infection. Light micrograph of cells from a patient's lung showing cytomegalic inclusion disease, a cytomegalovirus infection. Cytomegalovirus (CMV) particles invade cell nuclei (small dark bodies), causing the appearance of darker bodies within them (inclusion bodies). CMV infection is common, and usually produces no symptoms. In some cases, however, it may lead to a disease resembling glandular fever (mononucleosis). In immunosuppressed patients, the disease is more serious. Also, pregnant women can pass the virus to their foetus, which can cause malformations and brain damage. Magnification unknown.