Development and validation of a chemiluminescent immunodetection assay amenable to high throughput screening of antiviral drugs for Nipah and Hendra virus

There are currently no antiviral drugs approved for the highly lethal Biosafety Level 4 pathogens Nipah and Hendra virus. A number of researchers are developing surrogate assays amenable to Biosafety Level 2 biocontainment but ultimately, the development of a high throughput screening method for directly quantifying these viruses in a Biosafety Level 4 environment will be critical for final evaluation of antiviral drugs identified in surrogate assays, in addition to reducing the time required for effective antiviral drug development. By adapting an existing immunoplaque assay and using enzyme linked immunodetection in a microtitre plate format, the current experiments describe a simple two step assay protocol involving an overnight virus inoculation of Vero cell monolayers (with or without antiviral drug treatment) at Biosafety Level 4, followed by cell fixation and virus inactivation enabling removal of plates from the Biosafety Level 4 laboratory and a subsequent immunodetection assay using a chemiluminescent horse radish peroxidase substrate to be performed at Biosafety Level 2. The analytical sensitivity (limit of detection) of this assay is 100 tissue culture infectious dose50/ml of either Nipah or Hendra virus. In addition this assay enables linear quantitation of virus over three orders of magnitude and is unaffected by dimethyl sulfoxide concentrations of 1% or less. Intra-assay coefficients of variation are acceptable (less than 20%) when detecting a minimum of 1000 tissue culture infectious dose50/ml of either virus although inter-assay variation is considerably greater. By an assessment of efficacies of the broad spectrum antiviral Ribavirin and an experimental fusion inhibitory peptide, this assay reveals a good correlation with previously published fluorescent immunodetection assays. The current experiments describe for the first time, a high throughput screening method amenable for direct assessment of live henipavirus antiviral drug activity.