Production, Isolation, and Partial Characterization of Three Foot-and-Mouth Disease Virus Temperature-Sensitive Mutants

Abstract

Three high temperature-sensitive (ts) mutants of foot-and-mouth disease virus were characterized by their relative abilities to grow at 33 or 38.5 C, to kill infant mice, to infect guinea pigs, and to produce foot-and-mouth disease in steers. Mutants ts-24 and ts-42 did not grow at 38.5 C; both may have produced considerable quantities of noninfectious virus particles at 33 C. A third mutant, ts-22, appeared "leaky" because it multiplied to a limited extent during prolonged incubation at the nonpermissive temperature. Mutant ts-42 was pathogenic for infant mice, whereas ts-22 and ts-24 were essentially apathogenic. Mice were protected against the lethal effects of the wild-type (wt) virus if injected 1 week earlier with ts-22, apparently as a result of specific antibody development. One-half of the guinea pigs injected with the mutant viruses showed lesion development, but only at the site of injection. Antibody development was also much less than in those animals injected with the wt virus. The onset of FMD in steers was delayed and the severity of the disease was diminished after intradermalingual injection of the mutant viruses.

Isolation and preliminary characterization of temperature-sensitive mutants of encephalomyocarditis virus

“…Temperature-sensitive virus mutants have been isolated in many virus families. Within the Picornaviridae, temperature-sensitive mutants have been isolated from poliovirus (7), foot-andmouth disease virus (13,20,21), and mengovirus (2, 10). I have isolated temperature-sensitive mutants of encephalomyocarditis (EMC) virus because I wished to find mutants where the cleavage of viral precursor proteins is defective in mutant-infected cells at the nonpermissive temperature.…”

Further studies of the physical and metabolic properties of foot-and-mouth disease virus temperature-sensitive mutants

“…Mutant ts-22 was reported to replicate to a limited extent during long-term growth in primary BK cultures at 38.5 C and was therefore considered "leaky" (12). "Leaky" viruses generally multiply better under liquid medium than under solid overlay (7).…”

“…This assay for RNA synthesis in mixed infections at the nonpermissive temperature may prove to be a more critical and simpler method to screen for complementation between RNAmutants. Mutant ts-24 may contain defects both in the genes controlling mouse pathogenicity and in those related to ability to replicate at 38.5 C (12). Thus, several apparently diverse functional events may be controlled by genes within the same complementation group.…”

“…Viruses. Type A, subtype 24, FMD virus (wild type [wtl) was mutagenized with 5-fluorouracil as described previously (12). Mutants were initially selected that produced plaques well at 33 C (permissive temperature) but poorly, or not at all, at 38.5 C (nonpermissive temperature).…”

“…Recently, three ts mutants of type A24 FMD virus were isolated and characterized by their growth in tissue culture and several animal species (12). Mutant ts-22 was considered "leaky" because of its limited growth at the nonpermissive temperature (38.5 C), whereas ts-24 and ts-42 were unable to produce plaques under agar at this temperature.…”