Cytomegalovirus

• Virus isolation and cell culture
The detection of CMV by inoculation of specimen in human embryonic lung or foreskin fibroblast monolayers and identification of the slowly developing, focal CPE that is characteristic of CMV. This approach is slow may take up to 3 weeks for CPE to appear in culture but shell vial s can reduce the time of detection to as little as 1 day (Nauschuetz, 2000).

Human cytomegalovirus replicates only in fibroblast cells (not in epithelial cells).The virus is slow-growing and thus foci are small and discrete. Characteristic eosinophilic "owl-eye" inclusions are evident in the nuclei of infected cells (Stannard, 1996)
• Serology
Serologic evidence of recent primary CMV infection depended on the demonstration of conversion from IgG antibody negative to positive or demonstration of IgM antibody. Tests for IgM antibody to CMV often lack specificity for primary infection because of false-positive tests or because patients with past infection may have IgM antibody to CMV (Lazzarotto et al., 1999). Antibody tests are not useful in the diagnosis of CMV disease in the immunocompromised host. Although detection of IgM antibody to CMV has been used to diagnose congenital CMV infection, viral isolation techniques are more accurate and are preferred (Zanghellini et al., 1999).
• Detection of viral antigen and nucleic acid
Widely used non culture assays for detection of CMV are detection of pp65 antigen in white blood cells (WBCs) and PCR detection of CMV DNA. These methods are clearly more sensitive than viral isolation for detection of CMV in blood, and both have been extensively evaluated in immunocompromised patients. A number of other non culture methods for detection of CMV have been studied, including detection of antigens by EIA, hybridization techniques, RNA amplification, and hybridization techniques (Hebart et al., 1998).
Detection of pp65 antigenemia has the advantage that it yields results rapidly and is commercially available; allowing standardization between centers and the major disadvantage to detection of pp65 antigenemia is that samples must be tested within a few hours of collection. PCR has the advantage that it can be used to detect CMV DNA in samples other than WBC, such as whole blood, plasma, cerebrospinal fluid, or bronchoalveolar lavage fluid (Sia and Patel, 2000).