Add CCID50 and TCID50?

[Gunther Schadow]

TCID and CCID seem to be closely related, perhaps even equivalent. Here are two references:

WHO EXPERT COMMITTEE ON BIOLOGICAL STANDARDIZATION (55th Edition) WHO Technical Report #932; copyright 2005 ....

5. Virus titration for infectivity

Each working seed lot should be assayed for infectivity in a sensitive assay in cell cultures.

• A plaque assay may be used in Vero or other sensitive cells. Titre should be determined by counting the number of visible plaques developed, and results recorded as PFU/ml.
• An immunofocus assay may also be used to measure virus titre. The assay is based on the visualization of infected areas of a cell monolayer by probing with dengue serotype-specific monoclonal antibodies. Results should be recorded as FFU/ml.
• A tissue culture infectious dose assay may also be used to determine virus titre. Results should be recorded as CCID50/ml.

If international reference standards become available, immunizing doses should be expressed as relative potencies rather than CCID50 because experience shows that this reduces variability between assays.

......

Quantitation of Cytomegalovirus: Methodologic Aspects and Clinical Applications

Michael Boeckh1,* and Guy Boivin2

Clinical Microbiology Reviews, July 1998, p. 533-554, Vol. 11, No. 3 0893-8512/98/$04.00+0 ....A somewhat less precise method of quantifying CMV in tissue culture is determination of the TCID50. With this method, the virus titer can be determined by determining the highest dilution of the specimen which produces a cytopathic effect in 50% of the cell cultures or wells inoculated (151).

151. Schmidt, N. J. 1989. Cell culture procedures for diagnostic virology, p. 78-79. In N. J. Schmidt, and R. W. Emmons (ed.), Diagnostic procedures for viral, rickettsial and chlamydial infections, 5th ed. American Public Health Association, Inc., Washington, D.C.

[Gunther Schadow]

CBER requests

TCID/CCID: CBER requests that the definition use the terminology "infectious" as originally proposed by CBER since infectious accurately conveys that there is the capability for this virus to be 'contagious' and spread to the cell next to it and form a readable output in the tissue culture setting. CBER's assessment was based on literature citations and use in the field.

Point noted, change made: [15635]