Antiviral susceptibility testing of cytomegalovirus from primary culture using shell vial assay to detect the late viral antigen

Testing the susceptibility of human herpesviruses to antivirals

Herpesviruses cause chronic lifelong infections in humans and may cause life-threatening diseases in immunosuppressed patients. Antiviral drugs targeted to viral DNA polymerase, such as acyclovir, penciclovir, ganciclovir, foscarnet and cidofovir, are currently available and have been proven to be efficient against clinical symptoms of herpesvirus infections. The resistance of herpesviruses to these drugs is associated with specific mutations of viral genes encoding either DNA polymerase or enzymes phosphorylating nucleoside analogs. Resistance is detected and characterized by means of specific susceptibility assays, which can be classified as phenotypic, genetic and functional. These tests are used both to investigate novel antiviral compounds and look for the emergence of resistant viruses in treated patients in case of clinical failure. Although susceptibility assays are often time consuming and present some limitations regarding the interpretation of their results, their use in the monitoring of antiherpetic treatments should be promoted and improved, in parallel to the development of novel efficient drugs.

Valganciclovir: what is the status in solid organ transplantation?

Prophylactic drug therapy for cytomegalovirus disease in solid organ transplant recipients is effective and simple to implement, but it is associated with patient nonadherence and viral resistance. Recent data show that the efficacy and safety of oral ganciclovir and oral valganciclovir are similar. However, three large daily doses of oral ganciclovir are required, which is inconvenient, and viral resistance can develop to the drug. The single daily dose and lack of viral resistance are advantages of valganciclovir. This has become the primary agent for the prevention of cytomegalovirus disease. Current trials are underway to determine its effectiveness for treatment of cytomegalovirus disease, the optimal length of prophylaxis, and the safety and efficacy of a syrup formulation in children.

New strategies for prevention and therapy of cytomegalovirus infection and disease in solid-organ transplant recipients

In the past three decades since the inception of human organ transplantation, cytomegalovirus (CMV) has gained increasing clinical import because it is a common pathogen in the immunocompromised transplant recipient. Patients may suffer from severe manifestations of this infection along with the threat of potential fatality. Additionally, the dynamic evolution of immunosuppressive and antiviral agents has brought forth changes in the natural history of CMV infection and disease. Transplant physicians now face the daunting task of recognizing and managing the changing spectrum of CMV infection and its consequences in the organ recipient. For the microbiology laboratory, the emphasis has been geared toward the development of more sophisticated detection assays, including methods to detect emerging antiviral resistance. The discovery of novel antiviral chemotherapy is an important theme of clinical research. Investigations have also focused on preventative measures for CMV disease in the solid-organ transplant population. In all, while much has been achieved in the overall management of CMV infection, the current understanding of CMV pathogenesis and therapy still leaves much to be learned before success can be claimed.

Solid phase ELISA for determination of the virus dose dependent sensitivity of human cytomegalovirus to antiviral drugs in vitro

The main problems in determining the true in vivo susceptibility of human cytomegalovirus (CMV) to antiviral compounds are the influence of the size of the viral inoculum, the variation in the replication capacity of different CMV strains and the subjective evaluation of the inhibition of viral growth in the plaque assay. In this study, a specific assay was developed which reproducibly determines the sensitivity of primary isolates of CMV. The assay includes simultaneous virus titration and determination of the antiviral sensitivity. When individual virus doses were evaluated, the IC50 was generally dependent on the virus dose, except for resistant isolates, where the IC50 did not change irrespective of the dose of virus. The novel method of IC50 calculation takes into account all values derived from the linear part of the inhibition curve. This may better reflect the in vivo conditions, where the antiviral drug encounters different amounts of virus in different organs. Two human fibroblast-derived cell lines showed similar results.

Antiviral susceptibility testing-flow cytometric analysis (AST-FCA) for the detection of cytomegalovirus drug resistance

Antiviral susceptibility testing-flow cytometric analysis (AST-FCA), an application of flow cytometry in conjunction with cell culture, was developed to identify susceptibility of cytomegalovirus (CMV) isolates to the antiviral drugs ganciclovir (GCV) and foscarnet (PFA). The viral isolates used in this study were obtained from peripheral blood of AIDS patients. Among GCV-susceptible strains, the mean 50% inhibitory concentration (IC50) using AST-FCA was 18 microns (SI50 = 1.4). Among GCV resistant strains, the mean IC50 was 47 microns (SI50 = 3.6). For PFA, the mean IC50 was 80 microns (SI50 = 1.0) for susceptible strains. IC50s for strains resistant to PFA, showed no significant reduction of infectivity at the highest drug concentration (i.e., 200 microns PFA) tested. Additional analyses confirmed the accuracy of AST-FCA by parallel testing using plaque reduction assay. AST-FCA is a novel, nonisotopic, and relatively simple to perform laboratory procedure for the identification of CMV drug-resistant strains.

[Current status of human cytomegalovirus disease]

Human cytomegalovirus (HCMV) can establish lifelong persistence after primary infection with reactivation occurring as a result of immunosuppression. There is much evidence that molecular interactions between the immune system and the HCMV are responsible for immune escape. HCMV in many cells especially in mononuclear blood cells during latency are frequently the source of transmission and spreading and results in a variety of disorders. In this review some data about acute infection in immunocompetent host (mononucleosis, hepatitis), about intrauterine HCMV infection, about infection and endogenous reinfection in bone marrow and solid organ transplant recipients (pneumonitis) and about HCMV disease in AIDS patients (encephalitis, neuropathy, retinitis, colitis) are investigated. Moreover, HCMV associated vasculitis is described in patients with myocarditis, rheumatoid arthritis or polyradiculopathy. HCMV could play an important role in atherosclerosis. Several types of human malignancy have been linked to HCMV and it has been shown that HCMV ie genes upregulate expression of cellular oncogenes. The diagnosis of HCMV infection is carried out by viremia in cell culture using immediate early antigen staining, by antigenaemia which appears to be an early quantitative and predictive tool, by HCMV DNA detection using hybridization and PCR, and by IgM and IgG antibody evaluation. Two antiviral drugs are used for treatment: ganciclovir and phosphonoformic acid; few resistant clinical isolates have been reported. Specific gammaglobulin activity is discussed. HCMV vaccine is not available.