The whole development process of N. caninum tachyzoites
in vitro in J774 and Vero cells was observed daily for four consecutive
days by invert microscope (at the first inoculation). In this
study, in both cell lines the numbers of the extracellular parasites
increased at a slow to moderate rate on the first 3 days and released
rapidly on day 4 and reached the maximum number. Up
to day 3 post infection no significant differences were seen between
the numbers of the extracellular parasites released from
both cell cultures (P > 0.05). Nevertheless, at the 4th day, the tachyzoite
yield harvested from J774 cell culture showed a marked increase
(Fig. 1) and was significantly greater than the tachyzoite
yields harvested from the Vero cultures (P < 0.05) (Fig. 2).