- Volume 15, Issue 1, 1972

A strain of foot-and-mouth disease virus (O1 bfs 1860) was found to be comparatively stable in aerosols at relative humidities above 55%: the inactivation rate was greater at lower relative humidities.

Virus precipitated with ammonium sulphate or methanol was considerably more unstable than untreated virus at relative humidities below 55%: this instability was not due to residual precipitant not removed by dialysis. Virus precipitated by polyethylene glycol or centrifuged at high speed was as stable as untreated virus. Possible reasons for the instability of virus precipitated by ammonium sulphate or methanol are discussed.

Comparisons were made of the aerosol stabilities of eight strains of foot-and-mouth disease (FMD) virus suspended in bovine salivary fluid. The strains used were O1 bfs 1860, O1 pacheco, O1 lombardy, O2 brescia, A5 eystrup (tübingen), A22 iraq 24/64, Cnoville and Clebanon 3/69. The strains were compared as aerosol clouds 1 sec. old at different relative humidities and during storage for up to 60 min. at 70% and 55% relative humidity (RH). In aerosol clouds 1 sec. old all virus strains showed maximum survival of infectivity at 60% RH and above. Below 60% RH, infectivity was reduced and little infectivity was detected below 20% RH. At low RH the aerosol survival of the A strains was about 10-fold higher than that for the O and C strains. The strains differed significantly in stability during storage of aerosols at 70% or 55% RH. Decay rates ranged from 1.1 log./hr (O1 pacheco) to 3.2 log./hr (O1 bfs 1860) at 70% RH and from 2.1 log./hr (O1 pacheco) to 3.3 log./hr (A22 iraq) at 55% RH. At 55% RH the infectivity recoveries of some strains were too low for decay rates to be determined.

We have investigated the effect of ethidium bromide (EB) on synthesis of nuclear, virus and mitochondrial DNA in permissive cells infected with simian virus 40 (SV 40). In the presence of EB, no newly formed, closed-circular, mitochondrial DNA (M-DNA) could be detected by isopycnic EB-CsCl gradient centrifugation. Synthesis of nuclear and virus DNA was not inhibited by a concentration of 8 µg./ml., even though SV40-DNA and M-DNA are similar in their tertiary structure, in that both are supercoiled, closed-circular, double-stranded molecules. The yield of SV40 progeny under these conditions was not reduced nor was their specific infectivity affected, as compared to control values.

The polypeptides of cells which had been infected with adenovirus and pulse labelled with high specific activity [35S]-methionine have been examined by polyacrylamide gel electrophoresis followed by autoradiography. Five virus-particle polypeptides and at least five other polypeptides which appeared to be specific for the infected cell could be discerned. One of the latter polypeptides could be detected very early in infection and is shown to be one of the major components of the previously described P antigen. The experiments also show that in the absence of arginine in the tissue culture medium, the infected cells fail to synthesize the arginine-rich core polypeptide.

Cytoplasmic nucleocapsids of Semliki Forest virus were formed in BHK21 cells treated with canavanine under such conditions that virus RNA synthesis continued but no infectious virus was released. On the other hand, envelope protein synthesis was strongly inhibited. The canavanine nucleocapsids formed sedimented at 140s and contained 42s virus RNA and a protein indistinguishable from the normal protein by polyacrylamide gel electrophoresis. The canavanine nucleocapsids were not released from the cells.