Replication of human cytomegalovirus at supra-optimal temperatures is dependent on the virus strain, multiplicity of infection and phase of virus replication.

The kinetics of replication of five strains of human cytomegalovirus (CMV) were studied to determine the influence of (i) temperature, (ii) virus strain, (iii) m.o.i. and (iv) cell type. Relative to growth at 37 degrees C (m.o.i. = 3 to 9) eclipse periods were extended from 24 to 48 h at 33 degrees C and to 72 h at 40.5 degrees C. Yields were reduced at 33 degrees C and almost eliminated at 40.5 degrees C. No replication occurred in most instances at 40.5 degrees C and with 0.05 p.f.u./cell. Temperature shift studies (40.5 to 37 degrees C) indicated that the block to replication at 40.5 degrees occurred about 12 to 16 h p.i. resulting in little synthesis of CMV DNA or late antigens. The degree of inhibition of late functions at 40.5 degrees C is virus strain and m.o.i. dependent, but is not dependent on the type of fibroblastic cell used. These data suggest that persistent CMV infections are favoured at 40.5 degrees C.