Ex vivo differential virulence of L. infantum parasites. The time course of infection was followed counting (A, B) infected cells and (C, D) the number of parasites per infected cell. In cases in which the data was not normally distributed (P <0.05), a 2-sample t-test could not be used. We used the Mann-Whitney U test instead. Each value represents the mean ± SD from three independent experiments. Significant differences between BCN150 strain and the other isolates were determined, as indicated. *P <0.05, **P <0.01, **P <0.001; ns, not significant.