Studies on the spreading routes of Streptococcus spp. in rainbow trout ( Oncorhynchus mykiss )

• Main Authors: HUNG-LING WANG, 王宏玲
• Other Authors: 陳媺玫
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/64804527221831416482

碩士 === 國立臺灣大學 === 獸醫學研究所 === 89 === In order to realize the spreading routes of streptococci in rainbow trout ( Oncorhynchus mykiss ), we infected high-virulent strain ( R0726 ) and low-virulent strain ( RT-2 ) streptococci into rainbow trout fry experimentally, then isolated and stained immunohiatochemically streptococci at different time. The results showed that 2h postinfection, the streptococci were isolated from spleen of R0726 and RT-2 infected fry firstly. And 72h postinfection, streptococci could be isolated from all organs. According to the result of immunohistochemical staining, the streptococci get into fry by route of gill or gastrointestinal tract and spread to spleen, then liver and kidney, finally it developed systemic infection Besides, streptococci still could be isolated from spleen at 18d postinfection. The clinical signs of R0726 and RT-2 infected fry appeared suddenly at 3d postinfection and most serious from 3d to 6d, but clinical signs of fry infected with R0726 were more serious than those of RT-2 infected fry. The immunohistochemical findings showed that spreading routes of R0726 and RT-2 were similar. However, we found that the amount of R0726 in fry were much more than RT-2. Phagocytosed low-virulent strain ( RT-2 ) were killed whereas intracellular high-virulent strain ( R0726 ) seemed to survive within phagosomes of isolated macrophages of rainbow trout in the absence of anti-streptococci antibody and complement. Opsonisation of the streptococci was found to greatly enhance the killing activity of the rainbow trout macrophages.