C. Chantanachookin et al., HISTOLOGY AND ULTRASTRUCTURE REVEAL A NEW GRANULOSIS-LIKE VIRUS IN PENAEUS-MONODON AFFECTED BY YELLOW-HEAD DISEASE, Diseases of aquatic organisms, 17(2), 1993, pp. 145-157
A recently reported disease syndrome of Penaeus monodon in Thailand is
called 'yellow-head' or 'hua leung' in Thai. It is usually characteri
zed by light yellow coloration of the dorsal cephalothorax area and ge
nerally pale or bleached appearance of affected prawns. The yellow col
or in the cephalothorax region results from the underlying yellow hepa
topancreas showing through the translucent carapace in moribund shrimp
. In histological preparations of moribund yellow-head specimens for t
he light microscope, no consistent bacterial, fungal or parasitic agen
ts could be found. The lymphoid organs of yellow-head specimens showed
extensive abnormalities. These included obviously necrotic cells and
vacuolated cells with hypertrophied nuclei. Also evident were very den
sely basophilic, globose cytoplasmic inclusions located adjacent to so
me of the hypertrophied nuclei. Similar basophilic inclusions were fou
nd in interstitial hepatopancreatic tissue, in connective tissue under
lying the mid gut, in cardiac tissue, in gill tissue and in hematopoet
ic tissue. Transmission electron micrographs revealed the presence of
previously undescribed rod-shaped, enveloped virions in the cytoplasm
adjacent to the nuclei of cells from various tissues. Free virions wer
e also present in intercellular spaces. The virions were similar to th
ose of the insect granulosis viruses (Baculoviridae) in terms of cytop
lasmic location, size, morphology and development. However, they were
not occluded by granulin.