Squash mount of vermiform bodies (ATM) in shrimp hepatopancreatic tissue.

<p>(a) Low magnification photomicrograph showing 3 ATM with the central one inside an HP tubule. (b) Higher magnification photomicrograph showing an ATM containing cyst-like structures later found to be sloughed B-cells. (c) High magnification of an ATM stained with Rose Bengal to more clearly reveal its internal membranous structure.</p

ATM aggregation steps in H&E stained HP tissue sections in comparison to true gregarines.

<p>(a) Small, scattered membrane-lie structures in the HP tubule lumen. (b) More extended membranes beginning to aggregate in the tubule lumen. (c) Tighter aggregation of membranes bound by a continuous outer membrane and taking the shape of ATM. (d) Highly condensed ATM in a tubule lumen. (e) Accumulation of many individual ATM at the center of the HP near the midgut junction. (f) True gregarines clustered near the midgut junction and showing prominent nuclei.</p

HP tissue smear stained with hematoxylin and eosin to reveal ATM.

<p>The photomicrographs clearly show the vermiform morphology and the cyst-like contents inside or free.</p

TEM of an ATM structure containing an enclosed, sloughed and modified B-cell.

<p>Note the single-layer enclosing membrane and the internal complex of sloughed, modified microvilli.</p

TEM of unusual electron-dense particles in HP tubule crypts.

<p>(a) Low magnification of electron-dense particles of highly variable shape in the HP tubule lumen between layers of normal microvilli from facing epithelial cells. (b) High magnification of one of the electron-dense particles between the microvilli on the outside surface of an epithelial cell, possibly prior to cell entry. (c) High magnification of electron dense particles inside an epithelial cell with adjacent microvilli on the cell surface undergoing morphological changes. (d) Low magnification of an epithelial cell containing large numbers of electron dense particles and with microvilli in an advanced stage of transformation.</p

Semi-thin sections of HP tissue stained with toluidine blue.

<p>(a) Cross section of an HP tubule near the distal end showing densely stained particles in crypts formed by folds of the tubule epihelium and showing aggregated, transformed microvilli (ATM) in the tubule lumen. Note that microvillar layers of all the cells are intact. (b) Cross sections of HP tubules showing sloughed, transformed microvilli. (c) Cross section of an HP tubule showing a modified, sloughed B-cell in the tubule lumen with microvilli scattered over its surface. Also seen are tubule epithelial cells with normal microvilli and transformed mivrovilli, and one cell denuded of microvilli, undergoing lysis. (d) High magnification of clustered ATM at the center of the HP clearly showing an outer membrane enclosing multitudes of folded transformed microvilli. Some also contain enclosed, sloughed B-cells. Note many free transformed microvilli fragments surrounding the ATM.</p

TEM of steps in microvillar transformation and sloughing.

<p>(a) Low magnification of HP tubule epithelial cells showing normal and transformed microvilli and two denuded cells undergoing lysis. Also shown is an early stage in the aggregation of transformed and sloughed microvilli surrounded by an enclosing membrane. (b) Low magnification of HP tubule epithelial cells with transformed microvilli peeling from the cell surface, prior to cell lysis. (c) Higher magnification of the field from (b) clearly showing the difference between normal and transformed microvilli. (d) High magnification of HP tubule epithelial cells showing the tubular nature of transformed and peeled microvillar layers.</p

Gross signs of white feces syndrome WFS.

<p>(a) Floating, white fecal strings. (b) White fecal strings on a feeding tray. (c) White intestine of affected shrimp. (d) Golden brown intestine of an affected shrimp. (e) Photomicrograph of fecal string contents.</p