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Vibrio harveyi infection was found to occur in pond-reared black tiger prawn in Thailand. The diseased prawns with a hepatopancreatic infection of V. harveyi showed bacterial invasions and multiplication in the tubular lumens. This condition was followed by necrosis of hepatopancreatic cells and the thickened basal lamina, subsequent granulomatous encapsulation of the invaded tubules, and production of granulation tissue around granulomatous lesions. Heavy bacterial multiplication in the hepatopancreatic tubules caused systemic bacterial dissemination, which resulted in marked necrosis in the heart and lymphoid organ. On the other hand, two prawns with percuticular infection by V. harveyi had bacterial invasions in the subcuticular, spongy connective tissue in the telson, and systemic dissemination was followed by the occurrence of bacteriaphagocytizing hemocytes in the various tissues. Both types of isolates (chitinase positive and negative) were moderately pathogenic to prawn; intramuscular injection of 105-106 colony-forming units per prawn resulted in mortalities of 53–100%, and the chitinase-negative isolate was more virulent than the chitinase-positive isolate. The injected prawns exhibited systemic infection (as in prawns with a natural percuticular infection) in the moribund condition and granulomatous encapsulation in the injected sites on days 1–7 postinjection.
Jiravanichpaisal et al. (Tue,) studied this question.