Continuous high-speed rolling versus centrifugation for detection of herpes simplex virus

Rapid and accurate determination of the potency of varicella vaccine by quantitative polymerase chain reaction

The potency of varicella vaccines is currently determined by a plaque assay technique, which usually takes seven days and is laborious and has considerable inter- and intra-assay variability. Here, we report a new potency assay for varicella vaccine based on quantitative polymerase chain reaction in conjunction with a much more efficient virus infection step. Potency results can be obtained within 24h of infection and demonstrates acceptable accuracy and reproducibility when compared with the plaque assay, which relies on manual counting of plaques formed one week after viral infection. Using multiple vaccine lots from 7 manufacturers, we found no significant difference in infectivity determined between the new assay and plaque assay. The optimized conditions for viral infection and polymerase chain reaction are of significant value for the potency determination of the vaccine due to its rapidity, accuracy and the high throughput capacity of the assay.

The effect of rolling and orbital motion on herpesvirus replication in tube cultures and shell vials

BACKGROUND

Isolation of viruses from clinical specimens remains a viable diagnostic manoeuvre but positive isolation rates may be low and time to observe cytopathic effects (CPE) may be longer than preferred for optimal management. Both shell vial (SV) centrifugation and rolling of conventional tube cultures (TC) have been used to enhance the isolation process.

OBJECTIVES

To determine the effect of rolling and orbital motion on the replication of herpes simplex virus (HSV) and cytomegalovirus (CMV) TC and SV.

STUDY DESIGN

TC were inoculated with HSV or CMV at varying dilutions and subjected to rolling or incubated stationary. Samples were selected to determine the impact of motion on viral yield, time to CPE according to initial multiplicity of infection (MOI) and stage of the infection process. Similar studies were performed with SV centrifuged with virus followed by stationary incubation or not centrifuged but incubated on an orbital shaker.

RESULTS

Rolling HSV-infected TC 383 rotations per minute (RPM) (30.2 x g) for 4 days enhanced viral yields by 53-fold over TC without motion. The optimal RPM response for HSV replication occurred at 96 RPM (1.9 x g) where an 89-fold increase in viral yield was detected, P < 0.01. One-step growth studies at 0,2 and 96 RPM demonstrated enhancement of HSV replication at 2 and 96 RPM. TC infected with HSV at low MOI and rolled at 96 RPM had more CPE-positive cultures after 1-3 days than controls. Late in the infection process, no differences in CPE-positive were detected between rolled and non-rolled TC. Studies with CMV and rolling at 96 RPM resulted in more positive TC and greater CPE. SV that were not centrifuged but incubated for 16 h on an orbital shaker had significantly more HSV foci than those handled by a conventional SV method.

CONCLUSION

Our studies indicate that orbital motion and motion yielding a force near [Formula: see text] enhances the isolation and growth of HSV and CMV in TC and SV.

Laboratory techniques in the diagnosis of herpes simplex infection

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Physical and chemical methods for enhancing rapid detection of viruses and other agents

Viral replication events can be enhanced by physical, chemical, or heat treatment of cells. The centrifugation of cells can stimulate them to proliferate, reduce their generation times, and activate gene expression. Human endothelial cells can be activated to release cyclo-oxygenase metabolites after rocking for 5 min, and mechanical stress can stimulate endothelial cells to proliferate. Centrifugation of virus-infected cultures can increase cytopathic effects (CPE), enhance the number of infected cells, increase viral yields, and reduce viral detection times and may increase viral isolation rates. The rolling of virus-infected cells also has an effect similar to that of centrifugation. The continuous rolling of virus-infected cultures at < or = 2.0 rpm can enhance enterovirus, rhinovirus, reovirus, rotavirus, paramyxovirus, herpesvirus, and vaccinia virus CPE or yields or both. For some viruses, the continuous rolling of infected cell cultures at 96 rpm (1.9 x g) is superior to rolling at 2.0 rpm for viral replication or CPE production. In addition to centrifugation and rolling, the treatment of cells with chemicals or heat can also enhance viral yields or CPE. For example, the treatment of virus-infected cells with dimethyl sulfoxide can enhance viral transformation, increase plaque numbers and plaque size, increase the number of cells producing antigens, and increase viral yields. The infectivity of fowl plague virus is increased by 80-fold when 4% dimethyl sulfoxide is added to culture medium immediately after infection. The heat shocking of virus-infected cells also has been shown to have a stimulatory effect on the replication events of cytomegalovirus, Epstein-Barr virus, and human immunodeficiency virus. The effects of motion, chemicals, or heat treatments on viral replication are not well understood. These treatments apparently activate cells to make them more permissive to viral infection and viral replication. Perhaps heat shock proteins or stress proteins are a common factor for this enhancement phenomenon. The utility of these treatments alone or in combination with other methods for enhancing viral isolation and replication in a diagnostic setting needs further investigation.

Comparison of shell vial culture and the suspension-infection method for the rapid detection of herpes simplex viruses

Shell vial culture (SVC) and suspension-infection (SI) (simultaneous seeding of culture cells and inoculation of sample) were compared for the detection of herpes simplex virus (HSV) in clinical specimens. Conventional culture methods using mink lung cells or the Vero cell subline C1008 were also compared with each other and with SVC and SI. Additionally, SVC and SI were compared for quantitative determination of HSV infectivity. Compared with conventional culture with mink lung cells, culture with C1008 cells was 98% sensitive, and the sensitivities of SVC and SI were 94% and 93%, respectively. In quantitative determinations, titers of infectious HSV in positive clinical samples were a mean of five- to six-fold higher, as detected in SVC compared with SI titrations. For quantitative detection of infectious HSV, SVC was more sensitive than SI; however, for diagnosis of HSV in clinical specimens, no significant difference was observed between SI and SVC.

Suitability of infection of cells in suspension for detection of herpes simplex virus

Detection of herpes simplex virus in clinical specimens by the suspension-infection technique was compared with detection by conventional cell culture. The sensitivity and specificity of the suspension-infection technique compared with those of conventional culture were 95.9 to 98.2% and 97.5 to 100%, respectively, depending on the cell line used in the tests. The mean time to diagnosis by the suspension-infection technique was 1 day, compared with 4.8 days by conventional culture. Comparable detection of low-level positive specimens was observed with the methods. In a clinical setting, the isolation rates obtained by suspension-infection and conventional culture were indistinguishable. These results indicate that the suspension-infection method can be used for the detection of herpes simplex virus and can yield rapid diagnostic results without a time-consuming centrifugation step.