Abstract
Green monkey kidney cell (GMK) cultures were used to compare some biological properties between the prototype strain Cox. A-16 and strain 69-70, a representative strain which had been isolated from vesicular fluids of patients with hand-foot and mouth disease (HFMD). Some marker-tests of poliovirus were also applied tentatively to both strains. The results obtained are summarized as follows.
Strain 69-70 showed a resistance to anti-69-70 and anti-Cox. A-16 serum, but the prototype strain was readily neutralized by both sera. This character was not alterd by cells used in experiments for virus isolation, multiplication, and neutralization.
The infectivity of the prototype strain was 2 log units higher than that of strain 69-70. Electron microscopic observation suggested that many empty virions of strain 69-70 might have been produced.
There was a marked reduction in the plaque size and the efficiency of plating of the prototype strain under an acidic agar-overlay, whereas strain 69-70 was not affected with a wide range of bicarbonate concentration.
Heating at 50°C in the presence of AlCl3 was effective for stabilizing the infectivity of the prototype strain, but had no such significant effect on that of strain 69-70.
The effect of temperature on viral growth of both strains was examined in titration of infective virus at 40, 37, and 30°C. The prototype strain grew readily at these temperatures, but the growth of strain 69-70 was repressed under the same experimental conditions.
From the results obtained, it was suggested that the epidemic of HFMD occurring in Japan over a period from 1969 to 1970 might have been induced by the invasion of a new variant strain of Cox. A-16 virus.
