In Vitro Antiviral Testing

A key step in drug discovery is screening assays to assess antiviral activity. We offer a set of assays in key virus families. We can help you select appropriate assays for your specific compound and mechanism of action. We perform cytotoxicity analysis of the compounds to ensure your efficacy data are meaningful and within a reasonable therapeutic window. We can develop custom assays tailored to your specific program. If you don’t see what you need or have any other questions please contact us.

Cytopathic effect (CPE) screen. In this assay the test article is evaluated for its ability to inhibit CPE caused by the virus. Cells are pretreated with the test article and then infected with the virus of interest. After a virus-specific incubation period the cells are stained to quantify cell survival relative to an untreated virus-only control. This is our most inexpensive and fastest assay to get an idea of the overall antiviral activity of a test article. As an alternative to the CPE readout, we offer a cell-based ELISA for certain viruses: Instead of cell death we quantify the abundance of viral proteins as a marker of infectivity.

Neutralization assays. We offer two variations for evaluating neutralizing activity of a test article: Plaque-reduction neutralization (PRN) and microneutralization (MN). In both assays the virus is incubated with the test article before suitable cells are infected. For PRN, the readout is the number of plaques.  For MN, the readout is cell survival relative to an untreated virus-only control (i.e. similar to the CPE readout described above). For certain viruses we can establish a pseudotype-based neutralization assay with a luciferase readout.

Yield-reduction assays. This assay is a two-step procedure. Cells are incubated with the test article and then infected with the virus of choice. After a virus-specific incubation time the supernatants are harvested and the virus titers are determined using a method suitable for the selected virus. Titration methods include TCID50, plaque assay, and immunocytochemical staining (“immunoplaque”).

Hemagglutination-inhibition test (HAI). HAI is an assay used to test the efficacy of influenza vaccine candidates.  We offer HAIs against H1, H7 and H10 subtypes of influenza. The basis for the HAI is that antibodies from vaccinated animal serum samples will prevent virus-induced hemagglutination. Serum samples from vaccinated animals are tested in vitro to determine the minimum serum dilution that inhibits the hemagglutination. This is reported as the HAI titer of the serum.


Virus Family Genus Species Strain Details
Togaviridae Alphavirus


Venezuelan Equine Encephalitis



Flaviviridae Flavivirus

Dengue 1-4

Japanese Encephalitis

Yellow Fever





FSS 13025

Arenaviridae Arenavirus Junin Candid 1  
Orthomyxoviridae Influenza A
Influenza B




Bunyaviridae Phlebovirus
Rift Valley Fever
La Crosse



Poxviridae Orthopoxvirus Vaccinia NYCHBH  
Paramyxoviridae Pneumovirus Human Respiratory Syncytial Virus  
Herpesviridae Simplexvirus Herpes Simplex Virus