Comparison of RNAs and polypeptides of infectious pancreatic necrosis virus isolates from eel and rainbow trout

Viral diseases of wild and farmed European eel Anguilla anguilla with particular reference to the Netherlands

Diseases are an important cause of losses and decreased production rates in freshwater eel farming, and have been suggested to play a contributory role in the worldwide decline in wild freshwater eel stocks. Three commonly detected pathogenic viruses of European eel Anguilla anguilla are the aquabirnavirus eel virus European (EVE), the rhabdovirus eel virus European X (EVEX), and the alloherpesvirus anguillid herpesvirus 1 (AngHV1). In general, all 3 viruses cause a nonspecific haemorrhagic disease with increased mortality rates. This review provides an overview of the current knowledge on the aetiology, prevalence, clinical signs and gross pathology of these 3 viruses. Reported experimental infections showed the temperature dependency and potential pathogenicity of these viruses for eels and other fish species. In addition to the published literature, an overview of the isolation of pathogenic viruses from wild and farmed A. anguilla in the Netherlands during the past 2 decades is given. A total of 249 wild A. anguilla, 39 batches of glass eels intended for farming purposes, and 239 batches of farmed European eels were necropsied and examined virologically. AngHV1 was isolated from wild yellow and silver A. anguilla from the Netherlands from 1998 until the present, while EVEX was only found sporadically, and EVE was never isolated. In farmed A. anguilla AngHV1 was also the most commonly isolated virus, followed by EVE and EVEX.

Diversity of infectious pancreatic necrosis virus strains isolated from fish, shellfish, and other reservoirs in Northwestern Spain

A comparison was done of 231 strains of birnavirus isolated from fish, shellfish, and other reservoirs in a survey study that began in 1986 in Galicia (northwestern Spain). Reference strains from all of the infectious pancreatic necrosis virus serotypes were included in the comparison, which was done by neutralization tests and agarose and polyacrylamide gel electrophoresis of the viral genome. The neutralization tests with antisera against the West Buxton, Spajarup (Sp), and Abild (Ab) strains showed that most of the Galician isolates were European types Sp and Ab; however, many isolates (30%) could not be typed. Results from agarose gels did not provided information for grouping of the strains, since all were found to have genomic segments of similar sizes. Analysis of polyacrylamide gels, however, allowed six electropherogroups (EGs) to be differentiated on the basis of genome mobility and separation among segments, and a certain relationship between EGs and serotypes was observed. A wide diversity of electropherotypes was observed among the Galician isolates, and as neutralization tests showed, most of the isolates were included in EGs corresponding to European types Ab and Sp. Only 6.5% of the isolates had the electropherotype characteristic of American strains.

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.

Involvement of serine proteinase in infectious pancreatic necrosis virus capsid protein maturation and NS proteinase cleavage in CHSE-214 cells

An investigation of virus-specific protein maturation in infectious pancreatic necrosis virus (IPNV) infected Chinook salmon embryo cells (CHSE-214) was undertaken. The precursor protein (pVP2-1) of the major mature capsid protein (VP2) was processed sequentially from pVP2-1 to pVP2-2 and VP2. Experiments using serine proteinase inhibitors showed that the maturation of the VP2 was blocked in the pVP2-1 post-translational cleavage steps. A protinin, a potent proteinase inhibitor, at 800 μg ml(-1) blocked pVP2-2 to VP2 and the cleavage of VP4 (28 kDa) to VP4-1 (25 kDa). Therefore, our data showed that the maturation of the capsid protein (VP2) and cleavage of VP4 (NS proteinase) can be blocked by serine proteinase inhibitors.

Molecular relationships in infectious pancreatic necrosis virus

Infectious pancreatic necrosis virus (IPNV), a Birnaviridae with a double-stranded RNA genome of two segments, is an important aquatic pathogen. Previous characterizations of the RNA and polypeptide patterns of different IPNV isolates have uncovered a wide variety of electropherotypes. We used RNA fingerprinting analysis to study the quasispecies, heterogeneity, and rapid mutation characteristics of IPN viruses. Via cluster analysis of the RNA fingerprints, IPNV standard serotypes as well as T42G-, T24K- and T34G-related isolates were classified into 3 clusters corresponding to the AB, SP, and VR-299 serological types. The IPNV SP cluster represents a different evolutionary route from those of the AB and VR-299 clusters. The VR-299 clusters were separated into two groups, the T34G group were divided into two subgroups. The molecular relationships between these isolates can be correlated with the biological characteristics of these IPN viruses, for example, selective growth in EPC cells and adaptive replication at high temperatures.