The virus of canine distemper in cell culture: I. Adaptation of canine distemper virus to growth and serial passage in ferret kidney cell cultures and in BS-C-1 cell cultures

Abstract

The C.S.L. strain of virulent CDV, isolated from FK cell cultures prepared from an infected ferret, was adapted to grow in normal FK cell cultures. Adaptation was achieved after 3 rapid serial passages in FK cell cultures, interpolation of an adult ferret, and subsequent serial passage at 14 day intervals in FK cell cultures. CPE was enhanced in FK cell cultures which were rolled after infection. The more frequently the medium was changed the greater was the development of CPE. The FK cell culture adapted CDV produced a CPE in the diploid epithelial cell strain BS-C-1, and the virus was carried through 37 serial passages in these cells. Continued serial passage of the virus at 7 day intervals was possible only when the inoculum contained virus from mechanically disrupted cells. The rate of appearance of CPE was a function of the virus dose and the development of CPE was enhanced by frequent medium changes. Assays of CDV in BS-C-1 cells, in which the medium was changed daily, showed an increase in virus titre from day 0 to day 12, but there was no subsequent increase. The C.S.L. strain produced plaques in BS-C-1 cells overlaid with agar. Plaque counts increased from the 9th to the 14th day when they were maximal and they followed a linear relationship with dose. Assay of CDV by plaque development was more sensitive than the calculation of a TCID 50 using a flying cover-slip technique. CDV plaque assays were found to be reasonably precise and reproducible. The variance within assay pairs did not differ significantly from the variance between different assays performed on different occasions, using different ampoules and different batches of BS-C-1 cells.