Applications of Primary Cell Cultures in the Study of Animal Viruses **

In studies of the susceptibility of various primary tissue culture systems to arthropod-borne virus infection, it was found that host cell reactions induced by certain members of this group of viruses may take a variety of forms under the influence of various conditions.8'9""' Thus, a single virus strain may stimulate a different type of cellular response in each of two equally susceptible culture systems. For example, when Semliki forest virus was grown in chick embryo and rhesus monkey kidney monolayers, each culture system responded differently even though virus multiplication was proceeding at about the same rate in both as shown by the titration of infected tissue culture fluids in mice (Fig. 1). When these infected cell monolayers were examined microscopically, it was noted that the chick embryo cells were apparently undergoing rapid, irreversible, degenerative changes two days after virus inoculation, while only limited foci of somewhat questionable cytopathic changes were observed in the rhesus cultures inoculated under similar conditions. Plaques would form under an agar overlay, however, at the same rate in both types of cultures and independently of the cytopathic responses observed in the parallel fluid cultures.' It is, therefore, the purpose here to review such types of variations in cell culture responses induced by selected members of the arthropod-borne virus sero-groups.'