The effect of temperature on the growth of pox viruses in the chick embryo

Abstract

The ‘ceiling temperature’ of a pox virus has been defined as the maximum temperature (to the nearest 0·5° C.) of incubation at and below which that virus will grow and produce pocks on the chorioallantois of 12-day-old chick embryos, and above which no pocks appear.Ceiling temperatures have been estimated for: alastrim (2 strains), 37·5° C.; variola major (2 strains), 3·8° C.; ectromelia (3 strains) and monkey pox (1 strain), 39°C.; cowpox (2 strains), 40°C. Five strains of vaccinia and two of rabbit pox were all capable of pock formation at 40·5° C. Above this temperature difficulty was encountered because many embryos died. But the ceiling temperature for two strains of vaccinia and one strain of rabbit pox was probably 41° C. The Utrecht strain of rabbit pox produced some lesions at 41·5° C.—the highest temperature used.The ceiling temperatures of the viruses used were not correlated with their thermal stabilities at 55°C.in vitro. Thus vaccinia strain, Lederle-7 N, had a high ceiling temperature and a low thermal stability, while variola major had a low ceiling temperature and a high thermal stability. For this reason ceiling temperatures and thermal stability are regarded as distinct characters.In experiments with twelve of the seventeen viruses of which the ceiling temperatures had been determined, the virulence for the chick embryo was then measured. It was found that, in general, the higher the ceiling temperature of a virus the greater was its virulence for the chick embryo.The presentation of these results is followed by a brief discussion of their significance and potential use.

The use of ceiling temperature and reactivation in the isolation of pox virus hybrids

“…After inoculation the eggs were incubated at the required temperatures as previously described (Bedson & Dumbell, 1961 2). This suspension was sealed in a thin glass ampoule and completely immersed in a water bath at 55°C.…”

“…It is based on the observation that viruses of the variola-vaccinia group differ in the temperatures at which their growth on the chick chorioallantois (C.A.M.) is inhibited (Bedson & Dumbell, 1961). The maximum temperature at which lesions are produced (ceiling temperature) is a constant character of each of the viruses tested.…”

“…of eggs incubated at or above 38' C. (Bedson & Dumbell, 1961). This inhibition is removed if, 16 hr.…”

The Effect of Temperature on the Development of Sericesthis Iridescent Virus

“…"Ceiling temperatures" of the kind described for SlV have been reported for pox viruses by Bedson and Dumbell (1961). They believed the ceiling temperatures were the result of thermal denaturation.…”

A poxvirus antigen associated with pathogenicity for rabbits

“…The strains of vaccinia, rabbitpox, variola and cowpox viruses were from those listed by Bedson & Dumbell (1961). The additional strains of cowpox were those that had been used by Rondle & Dumbell (1962).…”