Tissue reaction to Glugea plecoglossi infection in its natural host, Plecoglussus altivelis.

The microsporidian Glugea plecoglossi induces in its fish host Plecoglossus altivelis a hypertrophic growth of the infected cells, resulting in formation of large xenomas. Early thin-walled xenomas did not elicit any reaction of the surrounding tissue. Later, however, coinciding with the mature xenoma being filled up with a growing mass of spores, proliferative inflammatory reaction sets in, changing gradually the xenoma into a granuloma. The granulation tissue grows into the spore mass. The spores are eliminated by macrophages and the granuloma undergoes involution. A complete functional reparation of heavily infected organs is hardly possible. Essentially, the tissue reaction was found to follow the pattern known in G. anomala infections in sticklebacks and in some other Glugea species initiating the formation of large xenomas.