ESTIMATION OF TITER OF VENEZUELAN EQUINE ENCEPHALOMYELITIS VIRUS PREPARATIONS FROM A SINGLE-DILUTION ASSAY
ARMY BIOLOGICAL LABS FREDERICK MD
Pagination or Media Count:
When suspensions of Venezuelan equine encephalomyelitis VEE virus were injected intracerebrally into groups of mice, a nearly linear relationship was observed between the concentration of the virus injected and the mean reciprocal time-to-death of the mice. A total of 91 VEE preparations were assayed in duplicate, and, by plotting the relationship between the reciprocal time-to-death for mice given the .000001 dilution of virus and the MICLD50 mouse intracerebral challenge, LD50 response values for the virus preparations, a reference curve was established. Using this reference curve, it was possible to estimate directly the LD50 values of virus suspensions of unknown concentration from the mean reciprocal time-to-death of a group of mice injected with a single dilution. In this work, the number of mice used was reduced by 62.5, the titrations were complete in 3 to 5 days compared with the usual 10 to 14 days, three to four times as many assays could be done in a day, and no assays had to be repeated since end points were not missed. The precision of the single-dilution assay compared favorably with that of the LD50 titration.