Review on milky haemolymph syndrome caused by rickettsia-like bacteria ( RLB) on spiny lobster and experimental culture of RLB on grouper embryonic cell line (GE)

Abstract

Spiny lobster is a high economical value marine animal which is cultured popularly in the Central Vietnam. Although spiny lobster culture brings rather high profit, it is also very risky due to many factors. Among them, the newly emerged disease since 2006 called Milky Haemolymph Symptom (MHS) or Milky Disease (MHD) is of most significant ones. The disease was named as the infected lobsters have the dull haemolymph with milky color. It spreads with incredible fast speed and has heavily damaged lobster culture regions in Vietnam particularly during 2006-2008. Pathogen analysis led to the revelation of one small Gram negative, curved-rod shape bacterium, thriving with high population in the disease lobsters’ haemolymph. As this pathogen was unable to grow in normal culturing media and was shown to be intra-cellularly present, it was suggested to belong to Rickettsia genus, a genus of obligated intracellular parasite microorganisms, and named as RLB-MHS. Until now, to our understanding not any study was able to characterize further this pathogen. Therefore, this study provided a summarized look focusing on the causative agent of Milky Haemolymph Symptom in spiny lobster culture in Vietnam. In addition, it presented primary steps in studying the pathogen including collecting samples from infected spiny lobsters, isolating the pathogen from the haemolymph, culturing the pathogen in the animal cell and confirming the presence of the pathogen using 16S rRNA gene sequencing. In particular, this study is the first one having cultured successfully Rickettsia in animal cell line using grouper embryonic cell line. This success would serve as a critical step for further research on this kind of pathogen in our laboratory. Keyword: Milky Haemolymph Symptom, Spiny Lobster, Rickettsia, animal cell culture