Browsing by Author "Nakai, Toshihiro"
ArticleLD de la Peña, H Koube, T Nakai & K Muroga -
Fish Pathology, 1997 - Japanese Society of Fish PathologyIn Japan, vibriosis caused by Vibrio penaeicida usually occurs in cultured kuruma prawn (Penaeus japonicus) during summer and fall. The causative bacterium can easily be detected from overtly diseased prawns, but from apparently healthy prawns the detection rate is low. The results of the conventional isolation method of the pathogen does not seem to reflect the true carrier rate because more prawns often come into overt infection after collection-transport-acclimation procedures, although such data have not been published. In the present study, transport stress was given to apparently healthy prawns to verify the above phenomenon.
ArticleWhen Japanese eels (Anguilla japonica) were injected intramuscularly (IM) with ferric ammonium citrate (FAC) at a sublethal dose of 10 µg/g and followed by IM-injection with various doses of Vibrio anguillarum, FAC injection enhanced greatly the virulence of the pathogen to eels, lowering the LD50 value from 107.9 to 104.2 CFU/100 g. Similar effects were obtained with ferrous sulfate and ferric chloride in eels. However, such a virulence-enhancing effect of FAC was scarcely observed in ayu (Plecoglossus altivelis), which has high susceptibility to the pathogen by nature. It was also found that addition of FAC (10 µg/ml) in fish sera accelerated the bacterial growth in vitro but the effect was much greater in eel serum than in ayu serum. The results of these in vivo and in vitro experiments demonstrated that the availability of free iron in host fish would have a significant influence on the pathogenesis of V. anguillarum infection.
ArticleLD de la Peña, T Nakai & K Muroga -
The Israeli Journal of Aquaculture-Bamidgeh, 1998 - The Society of Israeli Aquaculture and Marine BiotechnologyTo estimate the portal of entry of Vibrio penaeicida in kuruma prawn (Penaeus japonicus), immersion and oral infection experiments were conducted with pre-treated and intact prawns. In immersion challenge, V. penaeicida produced 30% mortality in the shell-removed group at both 108 and 107 CFU/ml doses while in the eye-cut group, mortalities were 44% and 13% at 108 and 107 CFU/ml, respectively. In the intact group, 10% mortality was observed at 108 CFU/ml and no mortality at 107 CFU/ml after two weeks. The pathogen produced high mortalities in the orally incubated group, the median lethal dose (LD50) being 103-104 CFU/animal. In the groups given V. penaeicida-inoculated kuruma prawn meat and V. penaeicida-contaminated commercial pellets, mortalities within 60 days were 10% and 20%, respectively. These results suggest that the main portal of entry of V. penaeicida is the gastro-intestinal tract although the cuticle (epidermis) or wounds can also be portals.