MORPHOLOGICAL EVIDENCE FOR A SINGLE BACTERIAL ETIOLOGY IN TEXAS NECROTIZING HEPATOPANCREATITIS IN PENAEUS-VANNAMEI (CRUSTACEA, DECAPODA)

Texas necrotizing hepatopancreatitis (TNHP) is an economically significant disease of the marine shrimp Penaeus vannamei cultured in Texas, USA, shrimp farms. Since first recognized in 1985, the disease has occurred seasonally, and it has inflicted serious crop losses of 20 to 90 % nearly every year in farms located in southern Texas. Two descriptive papers have been published on the histopathology and ultrastructure of the hepatopancreas of shrimp with TNHP, and the authors of both papers concluded that at least 2 distinctly different species of intracellular bacteria were present in the infected cells. Morphological evidence is presented in this paper that supports the contention that the 2 morphological types, a rickettsia-like form and a helical form as previously reported, are morphological variants of the same species of bacteria.