The pathologic cycle of the infection of the microsporidian Microgemma ovoidea (Thèl., 1895) Amigó et al. 1996 in the liver of the Red Band Fish (Cepola macrophthalma L.)

Abstract

Pathologic study of the lesions caused by Microgemma ovoidea has shown that after the formation of the xenoma (stage 1), the parasitized cell is infiltrated by host macrophages (stage 2) and quickly encysted by the activity of fibroblasts that form a xenoma wall composed of collagenous fibers (stage 3). The phagocytic activity of the macrophages leads to the formation of a granuloma (stage 4) in which the cyst contents comprise macrophages filled with phagocytosed spores. This phagocytic activity is limited by the fact that some parts of the microsporidian spores, such as the spore walls, cannot be lysed by macrophages, which leads to the formation of fused giant cells containing nondigestible spore remnants. The final step in the process is healing (stage 5), in which some cells may start proliferating to regenerate the damaged area. Nevertheless, the host occasionally fails to control M. ovoidea infections. This failure can take two forms: bursting of the granuloma, or the appearance of secondary infections in granulomas, probably through parasitism of macrophages.