Abstract
Toxoplasma gondii is an obligate intracellular parasite infecting up to one third of the human population. The central event in the pathogenesis of toxoplasmosis is the conversion of tachyzoites into encysted bradyzoites. A novel approach to analyze the structure of in vivo-derived tissue cysts may be the increasingly used computational image analysis. The objective of this study was to quantify the geometrical complexity of T. gondii cysts by morphological, particle, and fractal analysis, as well as to determine if it is impacted by parasite strain, cyst age, and host type. A total of 31 images of T. gondii brain cysts of four type-2 strains (Me49, and local isolates BGD1, BGD14, and BGD26) was analyzed using ImageJ software. The parameters of interest included diameter, circularity, packing density (PD), fractal dimension (FD), and lacunarity. Although cyst diameter varied widely, its negative correlation with PD was observed. Circularity was remarkably close to 1, indicating a perfectly round shape of the cysts. PD and FD did not vary among cysts of different strains, age, and derived from mice of different genetic background. Conversely, lacunarity, which is a measure of heterogeneity, was significantly lower for BGD1 strain vs. all other strains, and higher for Me49 vs. BGD14 and BGD26, but did not differ among Me49 cysts of different age, or those derived from genetically different mice. The results indicate a highly uniform structure and occupancy of the different T. gondii tissue cysts. This study furthers the use of image analysis in describing the structural complexity of T. gondii cyst morphology, and presents the first application of fractal analysis for this purpose. The presented results show that use of a freely available software is a cost-effective approach to advance automated image scoring for T. gondii cysts.
Highlights
Toxoplasma gondii (T. gondii) is an obligate intracellular parasite belonging to the phylum Apicomplexa that can infect all warm-blooded animals, including humans
Images of T. gondii cysts analyzed in this paper were obtained in two ways, by selection from the photo archive of strains isolated and maintained in the Serbian National Reference Laboratory for Toxoplasmosis (NRLT), and from cysts harvested from mice infected for this study
We analyzed images of T. gondii cysts obtained from brain homogenates of mice infected with four different parasite strains (BGD1, BGD14, BGD26, Me49) in the same host (SW); Me49 cysts obtained at two different time points (6 and 12 weeks) in the same host (BALB/c); and Me49 cysts obtained from two different hosts (BALB/c and Swiss Webster (SW))
Summary
Toxoplasma gondii (T. gondii) is an obligate intracellular parasite belonging to the phylum Apicomplexa that can infect all warm-blooded animals, including humans. It is considered as one of the most successful parasites on the Earth, estimated to infect up to one third of the human population [1]. The three infectious life stages of T. gondii are rapidly proliferating tachyzoites, slowly growing bradyzoites (inside tissue cysts), and sporozoites (inside oocysts). During its complex life cycle, tachyzoites differentiate into bradyzoites, which in an immunocompetent host form tissue cysts, predominantly in the central nervous system and muscles [3]. Encystment is recognized as a central event in the pathogenesis, persistence, and transmission of toxoplasmosis
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