3 to determine if and how it is impacted by a number of parasite or host factors. Additionally, morphological and particle analyses of T. gondii cysts were applied to gain further insight into the cyst 73 shape uniformity, as well as to a possible correlation between the cyst size and the number of parasites. Perimeter Area y Circularit   circularity values close to 1.0, whereas elongated shapes have very low circularity (close to 0.0). Cysts were transferred to black background images for subsequent particle analysis.
For particle analysis, images were first enhanced using histogram equalization. During this relative particle count (RPC) was determined following the local Bernsen auto-thresholding, watershed further segmented by a watershed algorithm for two reasons: a) it seems that, due to a low local border clearly separated particle areas. In that manner, all of the cyst cross-section images were subjected to an 148 automated processing and the obtained particle numbers, N p , were expected to be proportional to the Fig 2C. The FD was obtained as a negative slope of the best-fit regression line:
Each FD calculation is accompanied by the correlation coefficient, , describing a goodness of 2 r 193 fit of the regression line, in a particular case.
In the cumulative mass method, a probability of finding a certain pixel number within a given 
Lacunarity of a fractal set represents the ratio of the second-order moment (variance) to the 
In addition to the mentioned parameters, we defined another parameter measuring the 207 percentage of space covered by bradyzoites, and termed it 'packing density' (PD). The two-dimensional 208 analysis was performed on the cyst cross-sectional areas captured on microscope. Both particle analysis 209 and fractal analysis provided the number of black pixels in a considered cross section, N B . The total number of pixels in a cross section, N T , was known in all cases, which allowed the packing density 211 estimation as 212 .
(7)
The 3A; Fig 4A,B) . Lacunarity, on the other hand, differed among the strains, in that it was significantly lower 265 in the BGD1 strain in comparison to the three other ones (p≤0.001), as well as in BGD14 and BGD26 vs.
Me49 (Tukey p=0.044 and p=0.033, respectively), but not between BGD14 and BGD26 (p=0.99) (Fig 3B) . 
In an attempt to improve the understanding of the nature of the tissue cyst structural The analyzed cysts widely differed in diameter, with the cysts obtained from the experiment 299 being smaller, albeit not significantly, compared to historical (archived) cysts. This may be due to a bias 300 towards larger, more interesting cysts kept in a laboratory photo archive. 