Cytomegalovirus (CMV) - MegaMicro

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Cytomegalovirus (CMV)

Microbiology > Virology > DNA viruses > Herpes viruses

General Information and Structure: Cytomegalovirus (CMV) is a member of the betaherpesvirinae subfamily of herpesviruses. Replication in betaherpesvirinae is much slower compared to the alphaherpesvirinae (e.g., herpes simplex virus-1 and -2). CMV is ubiquitous human pathogen that has infected up to 80% of adults by the age of 40. It remains an important opportunistic pathogen in immunocompromised patients, especially those with HIV/AIDs. Similar to other herpesviruses, CMV has a dsDNA genome contained within an icosahedral nucleocapsid that is enveloped.

Pathobiology: CMV primarily infects monocytes, granulocytes, lymphocytes, and epithelial cells. It rapidly establishes a latent infection in monocytes, CD34+ hematopoietic progenitor cells, and endothelial cells. The virus has evolved many strategies to evade immune detection and promote latent infection including decreasing antigen presentation in MHC I and MHC II. In the immunocompetent person, reactivation is rare due to cell-mediated immune system mechanisms. When these mechanisms are suppressed (e.g., HIV/AIDs, corticosteroids), reactivation can occur.

Epidemiology: CMV is distributed worldwide and does not display seasonal fluctuations in incidence. Humans are the only reservoir and transmit CMV horizontally through sexual contact, blood, tissue, and other bodily fluids, or vertically through placental transmission, intrauterine, and breast milk/colostrum. Therefore, fetuses, infants, blood and organ recipients, and immunocompromised people are most at risk for becoming infected.

Laboratory Diagnosis: Typical requres demonstation of virus in tissue with tissue. May be detected in asymptomatic carrier/shedding states. Histologically, cytomegalic cells are seen by hematoxyline-eosin staining. These are enlarged cells with a dense, central, basophilic intranuclear inclusion body often referred to as an “owl’s eye”. Detection of the viral genome can be achieved through PCR of blood, biopsy, or urine samples. Serology for IgM antibody can also be used to demonstrate infection but is not generally clinically used.

Disease manifestations: The clinical manifestations are highly dependent on the population that is infected. In immunocompetent patients, the majority are asymptomatic; however, some may present with fever of unknown origin or mononucleosis (heterophile negative). Congenital infection, especially if the woman acquires the infection for the first time during pregnancy, can result in a severe disease called cytomegalic inclusion disease, which is characterized by intrauterine growth restriction, microcephaly, intracerebral calcifications, hepatosplenomegaly, thrombocytopenia, jaundice, and rash. Hearing and vision loss, mental retardation, and stillbirth can also result from congenital infection. These represent the most severe cases and many neonates are asymptomatic. Perinatal infection from breastfeeding typically causes no disease in healthy infants. Immunocompromised patients can have severe and life threatening diseases including pneumonia, retinitis, colitis, and esophagitis. In transplant patients, CMV infection can cause organ rejection.

Treatment: Antiviral therapies are mainly for immunocompromised patients and include ganciclovir, valganciclovir, cidofovir, and foscarnet.

Key Words:
1.       CMV
2.       Herpesvirus
3.       Cytomegalic cell
4.       Owl’s eye
5.       Cytomegalic inclusion disease

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