Plasmid profiling of Flavobacterium psychrophilum isolates from ayu (Plecoglossus altivelis altivelis) and other fish species in Japan

In order to evaluate the genetic variability of the causative agent of cold water disease (CWD), plasmid profiling was used to characterize Flavobacterium (F.) psychrophilum isolates (n = 169). Size analysis of plasmids in F. psychrophilum isolates (n = 128) from several fish species demonstrated that six kinds of plasmids were harbored, and ayu isolates had different profiles compared to other isolates. Moreover, multiple isolates (n = 41) from CWD outbreaks in 2002 to 2003 at a single ayu farm were examined to determine differences between isolates from successive outbreaks and showed different profiles by the sources of seedlings.

Nodavirus associated with pathological changes in adult spotted coralgroupers (Plectropomus maculatus) in Thailand with viral nervous necrosis.

The present study characterized viral nervous necrosis in sea cage-reared adult spotted coralgroupers (Plectropomus maculatus). Histopathological study showed extensive vacuolation and neuronal necrosis of the olfactory bulb and the optic lobe of the forebrain and the inner and outer nuclear layer of retina. Mild necrosis was observed in the spinal cord. Homogeneous intranuclear inclusion bodies were noted in the hyperplastic and hypertrophic glandular epithelial cells of the swim bladder suggesting viral etiology. Etiological diagnosis of VNN was confirmed by RT-PCR, immunohistochemistry and in situ hybridization. The immunohistochemistry and in situ hybridization gave strongly positive staining in the same area of the infected cells of the brain, spinal cord and retina correlating with histopathological changes. No positive reaction was detectable in the affected gas glandular epithelium and other organs, confirming the consistent neurotropism of this nodavirus. Nodavirus was mainly detected in the olfactory bulb of the brain. The result suggests nasal transmission was the major route of infection.