Hsin-Yiu Chou

Studies on transmission of white spot syndrome associated baculovirus (WSBV) in Penaeus monodon and P. japonicus via waterborne contact and oral ingestion

WSBV (white spot syndrome associated baculovirus) is considered to be the main causative agent of a recently reported disease which has resulted in serious mortality among cultured penaeid shrimp in Taiwan and is characterized by obvious white spots on the body. Shrimp infectivity tests of WSBV were carried out by means of waterborne contact and oral ingestion. Healthy juvenile P. monodon and P. japonicus and healthy P. penicillatus postlarvae were immersed in filtrates prepared from either diseased P. japonicus or diseased P. monodon, both of which exhibited marked white spot signs. Cumulative mortalities of the three tested shrimp species reached 100% within 4–6 days. Using PCR with a specific primer set, WSBV was first detected in the previously healthy P. monodon immersed in filtrate from diseased P. monodon 6 h postinoculation (h p.i.). At 24 h p.i. detection rates reached 90%, and even though the tested shrimp failed to show visible evidence of disease, they nonetheless suffered 33% mortality. The appearance of WSBV in experimentally infected P. penicillatus postlarvae was detected at 24 h p.i. and reached 100% by 72 h p.i. Healthy P. monodon fed with diseased P. japonicus as well as those fed with diseased P. monodon became 80–90% WSBV-positive 24 h p.i. by PCR and all of the tested shrimp died within 5 d. Obvious white spots appeared on the exoskeleton of shrimp whether they were infected by waterborne contact or orally. WSBV was found highly pathogenic to the three tested shrimp species and was readily transmitted across different penaeid shrimp.

Effect of heavy metal stressors and salinity shock on the susceptibility of grouper (Epinephelus sp.) to infectious pancreatic necrosis virus.

In the present study, attempts were made to clarify the effect of heavy metal stressors and salinity shock on the disease susceptibility of grouper fry (Epinephelus sp.) to infectious pancreatic necrosis virus (IPNV) infection. Zinc, cadmium and copper (5 ppm ZnCl2, 3 ppm CdCl2 and 1 ppm CuCl2) were used to treat groupers before and after virus infection. Cumulative mortalities in the experimental groups were 96-100% within 42 days. Only 5-15% mortalities were observed in most of the groups that were exposed to either heavy metals or virus infection alone. Subsequently, virus was re-isolated from the experimentally infected groupers, and copper concentration was measured in fish that had been exposed to CuCl2. We also investigated the effect of salinity shock (i.e. an abrupt change of salinity level from 33 ppt to either 40 ppt or 20 ppt) on susceptibility of grouper to IPNV. Similar results were obtained, mortalities of groupers in the experimental groups reached 80-100%. The results of the present study suggest that an IPN virus with only low pathogenicity could cause high mortality in groupers when combined with environmental stress.

Cloning of the Major Capsid Protein (MCP) of Grouper Iridovirus of Taiwan (TGIV) and Preliminary Evaluation of a Recombinant MCP Vaccine against TGIV

Fish iridoviruses cause systemic diseases with high mortality in various species of wild and farm-raised fish, resulting in severe economic losses. In 1998, we isolated a new epizootic iridovirus in cultured grouper (Epinephelus sp.) in Taiwan, thus named as grouper iridovirus of Taiwan (TGIV). We report here the cloning of TGIV major capsid protein (MCP). Phylogenetic analysis of the iridoviral MCPs confirmed the classification of TGIV into the Megalocytivirus genus. Recombinant TGIV MCP and GIV MCP were then generated to produce polyclonal antibodies. Western blot analysis revealed that the two antisera were species-specific, indicating no common epitope shared by the MCPs of the two viruses. We further assayed the potency of a subunit vaccine containing recombinant TGIV MCP. The vaccine effectively protected grouper from TGIV infection. The result demonstrated that MCP is a suitable antigen for anti-TGIV vaccines.

Complete Genome Sequence of Streptococcus iniae 89353, a Virulent Strain Isolated from Diseased Tilapia in Taiwan

ABSTRACT Streptococcus iniae 89353 is a virulent strain isolated from diseased tilapia in Taiwan. The full-genome sequence of S. iniae 89353 is 2,098,647 bp. The revealed genome information will be beneficial for identification and understanding of potential virulence genes of Streptococcus iniae and possible immunogens for vaccine development against streptococcosis.

TEMPERATURE-DEPENDENT PATHOGENICITY OF GROUPER IRIDOVIRUS OF TAIWAN (TGIV)

Grouper iridovirus of Taiwan (TGIV) is one of the most devastating infectious pathogens of grouper fry in Taiwan. As environmental temperature often plays an important role in the outbreak of diseases, we assayed the impact of different temperatures (18, 25 and 32℃) on TGIV infection both in vitro and in vivo. Cytopathic effect (CPE) characterized as cell rounding and lysis were observed in TGIV-infected grouper SB (swim bladder) cells at 25℃ and 32℃, but was absent at 18℃. With temperature rising to 32℃, the presence of pycnotic nuclei and chromatin margination became prominent in the infected cells, indicating an apoptotic death. The morphological feature of apoptotic cell was further supported by the observation under electron microscope. In addition, the apoptosis of TGIV-infected cells promoted by hyperthermia (32℃) was confirmed by the assays of DNA laddering, DNA content and annexin V staining. To measure the temperature impact on the defense in TGIV-infected host, grouper fry was experimentally infected with the virus at 25℃ and 32℃, respectively. Cumulative mortalities reached 100% in the fish held at 25℃ on day 10 post-infection, whereas only 37.5% at 32℃ at 2-week post-infection. In addition, the mortality in the infected fish of the 32-to-25℃ group skyrocketed to 97.5% by day 8. All together, the data suggest different impacts of temperatures on the pathogenicity of TGIV in grouper: while the lower temperature (18℃) adversely affects the propagation of TGIV, the hyperthermic temperature (32℃) promotes apoptosis to prevent the spreading of virus, resulting in higher resistance of the host against the virus.