Sequencing of the full coding region of both genomic segments of seven betanodavirus strains isolated from different farmed species in Spain and Portugal revealed that six were reassortants, exhibiting a red-spotted grouper nervous necrosis virus (RGNNV)-type RNA1 and a striped jack nervous necrosis virus (SJNNV)-type RNA2. Analysis of sequences of reassortant strains at both the genomic and protein levels revealed the existence of differences compared with type strains of both genotypes. These differences were greater in the polymerase sequence, which is remarkable because viral structural proteins generally diverge more rapidly than non-structural proteins. Changes in two amino acids observed in the SJNNV capsid protein might be involved in the colonization of new host species by these reassortant strains. In addition, a more extensive phylogenetic analysis, including partial sequences of both RNA segments of 16 other Iberian nodaviruses, confirmed the existence of reassortment between RGNNV and SJNNV.

During an epidemiological survey of viral encephalopathy and retinopathy (VER) in diseased sea bass Dicentrarchus labrax, a nodavirus isolate was recovered from net pen-reared sea bream Sparus aurata harboured in the same farming premises. After the virus was isolated and identified by immunofluorescence on SSN-1 cells, sequence analysis with a PCR product from the T4 region of the capsid protein gene indicated that the virus shared 100% identity with a pathogenic virus strain isolated from sea bass. Infection trials demonstrated the pathogenicity of the sea bream virus isolate for juvenile sea bass whereas sea bream infected with the same virus isolate remained asymptomatic even following intramuscular injection of virus. Nevertheless, the sea bream appeared to be a potential carrier of nodavirus, as juvenile sea bass became infected when maintained in a tank containing experimentally contaminated sea bream.

Porcine circovirustype 2 (PCV2) is recognized as a primary cause in post-weaning multisystemic wasting syndrome (PMWS). In this study, both PCV1 and PCV2 types were studied in pigs originating from PMWS-affected (+) and non-affected (−) herds from Brittany. PCV2 was identified by PCR in 100 % of animals from PMWS(+) herds and in 76 % from PMWS(−) herds, while PCV1 was not detected. The complete sequences of 38 PCV2 isolates were determined and 23 new variants were identified, displaying between 94·6 and 99·9 % nucleotide identity with one another. Although highly related to all the PCV2 sequences available in databases, the isolates from France gathered in a distinct subcluster. Compared with the 13 PCV2 from PMWS(+) farms, the 10 PMWS(−) sequences exhibited a slightly higher variability. No viral molecular marker specific to a pathogenic state could be identified, even by including other PCV2 variants isolated from PMWS-suffering animals from other countries. We concluded that the PMWS outbreaks in Brittany are most likely not due to the emergence of a new genotype of circovirus.

The reverse genetics technology for bluetongue virus (BTV) has been used in combination with complementing cell lines to recover defective BTV-1 mutants. To generate a potential disabled infectious single cycle (DISC) vaccine strain, we used a reverse genetics system to rescue defective virus strains with large deletions in an essential BTV gene that encodes the VP6 protein (segment S9) of the internal core. Four VP6-deficient BTV-1 mutants were generated by using a complementing cell line that provided the VP6 protein in trans . Characterization of the growth properties of mutant viruses showed that each mutant has the necessary characteristics for a potential vaccine strain: (i) viral protein expression in noncomplementing mammalian cells, (ii) no infectious virus generated in noncomplementing cells, and (iii) efficient replication in the complementing VP6 cell line. Further, a defective BTV-8 strain was made by reassorting the two RNA segments that encode the two outer capsid proteins (VP2 and VP5) of a highly pathogenic BTV-8 with the remaining eight RNA segments of one of the BTV-1 DISC viruses. The protective capabilities of BTV-1 and BTV-8 DISC viruses were assessed in sheep by challenge with specific virulent strains using several assay systems. The data obtained from these studies demonstrated that the DISC viruses are highly protective and could offer a promising alternative to the currently available attenuated and killed virus vaccines and are also compliant as DIVA (differentiating infected from vaccinated animals) vaccines.