The present invention has been made in view of a problem regarding stability, reproducibility, economy, and easiness of operation in studies for a monocyte- or dendritic cell-mediated infectious microorganism, and is directed to provide a method for maintenance culturing a monocyte- or dendritic cell-mediated infectious microorganism utilizing a monocyte having a proliferative capacity. The present invention is based on the finding that a dengue virus efficiently infects a proliferable human monocytic cell obtained by introducing a gene into a CD14-positive cell and a cell having a phagocytic capacity obtained by inducing the monocytic cell to differentiate (e.g., dendritic cell) and proliferates therein. Thus, provided is a novel method for evaluating a pharmaceutical such as a compound or a vaccine for treating an infection with a monocyte- or dendritic cell-mediated infectious microorganism.