Comparative studies of the multiplication of antigenically related poxviruses on the chorioallantoic membrane of the chick embryo.

Hahon, Nicholas (U. S. Army Chemical Corps, Frederick, Md.) and James J. Friel. Comparative studies of the multiplication of antigenically related poxviruses on the chorioallantoic membrane of the chick embryo. J. Bacteriol. 83:837-843. 1962.-A comparison was made of the general growth curves of several poxviruses, variola, alastrim, vaccinia, cowpox, rabbitpox, and monkeypox, on the chorioallantoic membrane of the chick embryo. All curves showed a lag period, followed by a tenfold increase of infectivity each 5 hr for approximately 20 to 25 hr, a peak growth level at 48 to 52 hr (except monkeypox), and a gradual decline after 72 hr. Closer examination of the lag period revealed a rapid decline of virus infectivity within 2 to 4 hr after inoculation and the manifestation of an eclipse phase for 4 and 6 hr with all poxviruses. The lag period was terminated with the detection of intracellular virus at 8 to 12 hr, followed by the appearance of extracellular virus 2 to 6 hr later. The proportion of extracellular to intracellular virus was 0.1 or less throughout the different stages of poxvirus growth. In contrast to findings with the other poxviruses, however, extracellular virus equaled or exceeded the quantity of intracellular virus during the latter stages of the growth curves of variola and alastrim viruses.