<em>Crithidia fasciculata</em> Exhibits a Monoxenic Behaviour In Vitro and In Vivo

There is increasing evidence on the occurrence of Crithidia spp. in patients presenting either cutaneous or visceral leishmaniasis, solely or associated with Leishmania. We analyzed the influence of temperature in the growth rate and morphology of two Crithidia fasciculata strains (a reference strain and one isolated from a patient), and the effect of the co-cultivation of Leishmania and Crithidia in parasite isolation, in the infection of macrophages in vitro, and also in infections of hamsters, BALB/c mice and sandflies. In culture, both Crithidia strains could undergo 32oC for 96 h, although major morphological alterations and a decrease in mitochondrial membrane potential were observed. At 34°C, there was an 80% reduction on the number of cells from the patient strain. Mixed cultivation of Crithidia-Leishmania led to the recovery of only Crithidia. In macrophages, C. fasciculata alone was virtually eliminated, and in the co-infection only Leishmania was recovered. The same was observed in vivo. Curiously, C. fasciculata is more resistant to Amphotericin B. Our results indicate that both C. fasciculata strains are unable to reproduce the pathogenic effect in vitro and in vivo models.