Effect of different preservatives during freezing process on infectivity of Leishmania major in mice model

Leishmanization (LZ) is an effective tool to prevent cutaneous leishmaniasis. Standardization of Leishmania is the main drawback of LZ. The aim of this study was to assess the effect of various preservatives on the infectivity of Leishmania. L. major harvested at different stages of growth; logarithmic, early and late stationary phases were frozen using various preservatives of saccharose, glycerol, trehalose, glucose, sorbitol, and dimethyl sulfoxide (DMSO). The harvested parasites were inoculated into BALB/c mice before and after freezing. The infectivity of the parasites was checked. IFA test was used to assess the rate of metacyclic parasite. The ratio of live Leishmania in different growth stages and various preservatives were 89.0% to 98.2%. The lesion development in groups of mice which received Leishmania in sacarose + glycerol or DMSO was started from 3rd week and at 5th week all the mice showed lesion. The group of mice which were inoculated with early or late stationary phases in saccharose + glucose, saccharose + glycerol, glycerol 15% or DMSO showed lesion from 4th to 5th week and in 100% showed lesions at 8th week. The rate of metacyclic parasites increases from log phase to early and late stationary phases. There was a correlation between percent of live parasite and the rate of lesion development in BALB/c mice. Saccharose 22.5% + Glyserol 22.5% were the most appropriate preservative to freeze L. major. IFA test is used to detect metacyclic Leishmania. A correlation was seen between the rate of lesion development in BALB/c mice and IFA positivity.