Fig. 3. Host reaction and pathology related to APXSc. (A–E) Granulomatous swirl lesions within the Tehuelche scallop, a common host reaction to APXSc infection. (A) Semithin section stained with toluidine blue, showing typical swirl-like lesion, where fibroblast-like hemocytes (black arrowheads) surround groups of parasites, commonly 4–8 (black arrow). A larger granuloma is then formed around a cluster of these groups, forming a kind of double granuloma. (B) ISH sections of a similar swirl lesion as in (A), note the formation of numerous groups of parasites, each group apparently within one hemocyte (host nuclei: white arrowheads) and surrounded by fibroblast like hemocytes (black arrowheads). The insert shows a higher magnification of a cluster of the parasites. (C–E) Granulomatous swirl lesions with apparently degenerating parasites (*), surrounded by fibroblast like hemocytes (arrowheads). (C) = HE) = ISH.. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)