Histopathological damage and localisation of Vibrio aestuarianus in diverse oyster tissues were studied on experimentally infected animals by histology and immunohistochemistry with a polyclonal antibody. Histological slides were scaned and are here presented.

On day 1, V. aestuarianus was detected as few foci in the gills of 5 out of 14 animals. Nevertheless, as early as this first day after bacterial contact, first signs of histological damage were observed. These lesions could be classified into three classes: (type 1) lysis of the sub-epithelial connective tissue in the mantle, (type 2) epithelial atrophy of digestive diverticula with dilation of the diverticulum lumen and (type 3) haemocyte lysis and/or infiltration by haemocytes and/or haemocyte agglutination in haemolymph vessels.

In oysters immersed in bacterial bath and sampled on day 4, intense colonization of all oyster tissues was observed. To be precise, stained bacteria-like cells were detected (i) in gills, as attached to epithelial cells or as isolated cells, (ii) around the digestive gland in connective tissues as well as attached or inside epithelial cells of the digestive tissue, (iii) in the mantle, in clusters in connective tissues, (iv) in between muscular fibres of the adductor muscle and (v) in the periphery of the sinus, vein or artery of different tissues. The disease progression on day 4 was associated with an increase of affected animals for the 3 types of lesions, as well as an increase in lesion intensity (an increase in the number of affected areas and significant atrophy of the digestive diverticula epithelium as compared with the control).

Finally, damage intensity increased reaching a maximum in moribund animals, in which V. aestuarianus was detected in every tissue of all the tested animals. These results confirmed the septicaemic characteristics of V. aestuarianus infection.