The growing global demand for seafood together with the limited capacity of the wild-capture sector to meet this demand has seen the aquaculture industry continue to grow around the world. A vast array of aquatic animal species is farmed in high density in freshwater, brackish and marine systems where they are exposed to new environments and potentially new diseases. On-farm stresses may compromise their ability to combat infection, and farming practices facilitate rapid transmission of disease. Viral pathogens, whether they have been established for decades or whether they are newly emerging as disease threats, are particularly challenging since there are few, if any, efficacious treatments, and the development of effective viral vaccines for delivery in aquatic systems remains elusive. Here, we review a few of the more significant viral pathogens of finfish, including aquabirnaviruses and infectious hematopoietic necrosis virus which have been known since the first half of the 20th century, and more recent viral pathogens, for example betanodaviruses, that have emerged as aquaculture has undergone a dramatic expansion in the past few decades.
The development of molecular diagnostic assays with increased sensitivity compared with conventional histological techniques is highly desirable for effective management of bonamiosis in cultured oyster stocks and wild populations. A real-time TaqMan PCR assay was developed for the specific detection of Bonamia species in infected oyster tissues. The TaqMan assay was shown to be significantly more sensitive than histopathology. Although a real-time TaqMan PCR assay is comparable with conventional PCR in terms of sensitivity, it offers the advantages that it is a rapid test and has a very low risk of sample cross-contamination. Furthermore, it can be optimised to quantify the parasite load in samples. The assay detected Bonamia isolates from Australia, New Zealand, Europe, Canada, Chile and the USA and therefore demonstrated genus specificity as tested in this study. KEY WORDS: Bonamia spp. · Real-time TaqMan PCR assay · Oyster Resale or republication not permitted without written consent of the publisherDis Aquat Org 71: [75][76][77][78][79][80] 2006 known to harbour Bonamia sp., an endemic isolate that has caused mortalities in the states of Victoria, Tasmania and Western Australia (Hine 1996, CochennecLaureau et al. 2003, Diggles 2003. Other isolates of Bonamia have been reported from O. chilensis in Chile (Campalans et al. 2000), Crassostrea ariakensis in North Carolina (Burreson et al. 2004) and O. puelchana in Argentina (Kroeck & Montes 2005). Taxonomic relationships between these isolates and described species within the genus need to be established.Although recent developments of PCR-based assays have partially addressed the limitations of histology (Carnegie & Cochennec-Laureau 2004), real-time PCR (polymerase chain reaction) has the potential to provide rapid and quantitative results. In order to establish an effective diagnostic capability that will help prevent the introduction of exotic Bonamia spp. and to avoid the spread of enzootic isolates, the development of a molecular-based diagnostic assay that allows rapid, reliable and sensitive detection of Bonamia spp. is required. This report describes the development of a real-time PCR assay capable of detecting Bonamia isolates with greater sensitivity than currently available methods. MATERIALS AND METHODSIsolates of Bonamia spp. Wild flat oysters Ostrea angasi, used as a source of Bonamia sp.-infected tissue, were collected and fixed in 95% ethanol, during the course of a survey on the health and genetics of stocks in 5 estuaries on the south coast of New South Wales, Australia (Heasman et al. 2004). European flat oyster O. edulis tissues, infected with isolates of B. ostreae and fixed in 95% ethanol, were obtained from France (6 samples) and the Netherlands (2 samples). Four bluff oyster O. chilensis tissues, infected with B. exitiosa and fixed in 95% ethanol, were obtained from New Zealand. In addition, DNA prepared from Bonamia-infected oysters O. edulis (Canada and USA) and O. chilensis (Chile) was included in the study. Furthermore,...
Koi herpesvirus (KHV) is the aetiological agent of an emerging disease (KHVD) associated with mass mortalities in koi and common carp and reported from at least 30 countries. We report the first isolation of KHV from koi and common carp in Indonesia and initial characterization of the isolates. Clinical signs, histopathology and virion morphology are similar to those of isolates from other countries. Phylogenetic analyses using the thymidine kinase gene amplified from each isolate and from carp tissue samples collected from KHVD outbreaks throughout Indonesia indicated that the Indonesian isolates are more closely related to the Asian than the European KHV lineage. Sequence analysis of two other variable regions between ORF29 and ORF31 (marker I) and near the start of ORF 133 (marker II) indicated that all Indonesian isolates displayed a marker I allele (I(++)) previously identified only in isolates of the Asian lineage. However, in the marker II region, all Indonesian isolates displayed the II(-) allele, which has been reported previously only amongst isolates of the European lineage, and nine of these displayed a mixed genotype (II(+)II(-)). The I(++)II(-) genotype has not been reported previously and appears to represent a new intermediate lineage that may have emerged in Indonesia.
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