Relationship between plaque size and the immunising ability of the foot-and-mouth disease virus SAT1 Nig 10/75

Abstract

Qualitative and quantitative laboratory tests on small and large plaque variants of the foot-and-mouth disease virus type SAT1Nig10/75 revealed an antigenic similarity which was confirmed by vaccine potency tests in guinea pigs. $ Virus preparations used for vaccines have often been shown to be heterogeneous in terms of the size of plaque they can elicit when plated on to cell monolayers. Where such plaque variants have been found to be stable, they have in many cases been linked with other changes in the virus population, e.g. attenuation (7, 10) and antigenic shift (6,12). COWA~ et al. (3) have suggested that plaque heterogeneity may be of importance in the production of vaccine antigens by showing the large plaque (LP) variant, of a type Asia, t foot-and-mouth disease virus to be four times more potent than the small plaque (SP) variant, when used to vaccinate small groups of cattle.Plaque size variants have been observed for six of the seven serot)~pes of footand-mouth disease (FMD) viruses when grown under various cultural conditions (8). To date, in most reported eases of plaque variants in FMD viruses, the large plaque variant is considered to be the "wild type" parent producing natural disease in animals (5).In the light of other workers' data, it was decided to investigate this phenomenon further, using a different serotype of FMD virus, and also paying particular attention to (1) the mass of antigen used to formulate vaccines and (2) the use of controlled vaccine trials :in guinea pigs to produce reliable data.During the growth of FMD virus strain SAT 1 Nig10/75 in BHK suspension cells in this laboratory, virus was assayed for infectivity by a plaque assay technique. Observations of the assay plates showed two different plaque types, one large (5--6 ram), and other small (1 mm). Both variants were isolated, plaque purified twice and given three BHK suspension {SP) or monotayer (LP) passage

The Pseudoknot Region of the 5′ Untranslated Region Is a Determinant of Viral Tropism and Virulence of Foot-and-Mouth Disease Virus

“…Previous studies also observed that several viruses and their mutant viruses could form different plaque sizes but present similar virus replication profiles (27, 37). For FMDV, it has been suggested that the plaque phenotype is not necessarily of significance for production of FMDV vaccine antigen (38). Here, our data also showed that the ability of rO-WT and rO-DPKs86 to form large or small plaques did not correlate with the ability of the viruses to replicate in BHK-21, PK-15, and BTY cells.…”