Inter-laboratory ring trial to evaluate real-time reverse transcription polymerase chain reaction methods used for detection of infectious pancreatic necrosis virus in Chile

Background: Infectious Pancreatic Necrosis Virus (IPNV) is the etiological agent of a highly contagious disease that affects salmonids. In Chile, the second worldwide salmon producer, IPNV causes great economic loss and is one of the most frequently detected pathogens. Due to its high level of persistence and the lack of information about the efficiency of its diagnostic techniques, the National Reference Laboratory (NRL) for IPNV in Chile performed the first inter-laboratory ring trial, to evaluate the sensitivity, specificity and repeatability of the qRT-PCR detection methods used in the country. Results: Results showed 100% in sensitivity and specificity in most of the laboratories. Only three of the twelve participant laboratories presented problems in sensitivity and one in specificity. Problems in specificity (false positives) were most likely caused by cross contamination of the samples, while errors in sensitivity (false negatives) were due to detection problems of the least concentrated viral sample. Regarding repeatability, many of the laboratories presented great dispersion of the results (Ct values) for replicate samples over the three days of the trial. Moreover, large differences in the Ct values for each sample were detected among all the laboratories. Conclusions: Overall, the ring trial showed high values of sensitivity and specificity, with some problems of repeatability and inter-laboratory variability. This last issue needs to be addressed in order to allow harmonized diagnostic of IPNV within the country. We recommend the use of the NRL methods as validated and reliable qRT-PCR protocols for the detection of IPNV.

Relationship between apoptosis and the BH2 domain sequence of the VP5 peptide of infectious pancreatic necrosis virus / Relación entre apoptosis y secuencia del dominio BH2 del peptido VP5 del virus de la necrosis pancreatica infecciosa

Objective. To determine whether the level of apoptosis induced by infectious pancreatic necrosis virus (IPNV) is related to the amino acid sequence of the BH2 domain of the VP5 protein and the level of infectivity. Materials and methods. Three IPNV strains were used, the VP2 protein gene was amplified for genotyping and the VP5 sequence was also obtained. The infectivity of the strains was calculated using the viral titer obtained at 12, 24, 36 and 45 hpi in CHSE-214 cells. The percentage of apoptosis in infected cells was visualized by TUNEL assay and immunohistochemistry (caspase 3 detection). Results. The V70/06 and V33/98 strains corresponded to genotype Sp, while V112/06 to VR-299; the amino acid analysis of the V70/06 strain allows its classification as middle virulent strain and V33/98 and V112/06 strains as low virulent ones; infection with the V112/06 strain produced a lower viral titer (p<0.05). The VP5 gene of the 3 strains showed four homologous domains to Bcl-2, however, the BH2 domain was truncated in V70/06 and V33/98 (12 kDa), being complete (15kDa) in V112/06, which also showed the Trp155 residue, equivalent to Trp188 considered as a critical factor for the function of Bcl-2. The average apoptosis was below 12%, showing no differences between strains (p>0.05). Conclusions. The results showed that the differences in the BH2 sequence of the VP5 protein, infectivity and the VP2 sequence are not associated with the modulation of apoptosis.

Objetivo. Determinar si el nivel de apoptosis inducido por cepas del virus de la necrosis pancreática infecciosa (IPNV) tiene relación con la secuencia aminoacídica del dominio BH2 de la proteína VP5 y el nivel de infectividad. Materiales y métodos. Se utilizaron tres cepas de IPNV; el gen de la proteína VP2 fue amplificado para genotipificación y se obtuvo la secuencia de VP5. La infectividad de las cepas se calculó mediante el título viral obtenido a 12, 24, 36 y 45 hpi en células CHSE-214. Los porcentajes de apoptosis en células infectadas se visualizaron mediante ensayo TUNEL e inmuno-histoquímica (detección de caspasa 3). Resultados. Las cepas V70/06 y V33/98 correspondieron a genotipo Sp, mientras que V112/06 a VR-299; el análisis aminoacídico relacionó a V70/06 como cepa de mediana virulencia y a V33/98 y V112/06 de baja virulencia; la infección con V112/06 produjo menor título viral (p<0.05). El gen VP5 de las 3 cepas presentó los cuatro dominios homólogos a Bcl-2; sin embargo, el dominio BH2 fue truncado en V70/06 y V33/98 (12 kDa); siendo completo (15kDa) en V112/06, que además, presentó el residuo Trp155, equivalente a Trp188 considerado factor crítico para la función de Bcl-2. El promedio de apoptosis fue inferior a 12%, no se observaron diferencias entre cepas (p>0.05). Conclusiones. Los resultados mostraron que las diferencias en la secuencia de BH2 de la proteína VP5, la infectividad y en la secuencia de la proteína VP2 no están asociadas con la modulación de apoptosis.

Infectious pancreatic necrosis virus (IPNV) enumeration through epifluorescence microscopy: technical aspects

A method for counting Infectious pancreatic necrosis virus (IPNV) through epifluorescence microscopy was analyzed in detail. Image processing and statistic considerations are included. The particle size of viruses was compared in different experimental conditions such as the staining of the virus with SYBR-Green I or with antibodies for specific fluorescence labeling of viral proteins. The type of surface used as mounting support was assayed as well. The results indicated that the most suitable method involves the mounting of the viral-containing suspension on a membrane filter followed by the staining with a monoclonal antibody specific for a viral protein combined with a FITC (fluorescein isothiocyanate)-conjugated secondary antibody.