Betanodavirus infection in bath‐challenged Solea senegalensis juveniles: A comparative analysis of RGNNV, SJNNV and reassortant strains

Abstract

Senegalese sole has been shown to be highly susceptible to betanodavirus infection, although virulence differences were observed between strains. To study the mechanisms involved in these differences, we have analysed the replication in brain tissue of three strains with different genotypes during 15 days after bath infection. In addition, possible portals of entry for betanodavirus into sole were investigated. The reassortant RGNNV/SJNNV and the SJNNV strain reached the brain after 1 and 2 days postinfection, respectively. Although no RGNNV replication was detected until day 3-4 postinfection, at the end of the experiment this strain yielded the highest viral load; this is in accordance with previous studies in which sole infected with the reassortant showed more acute signs and earlier mortality than the RGNNV and SJNNV strains. Differences between strains were also observed in the possible portals of entry. Thus, whereas the reassortant strain could infect sole mainly through the skin or the oral route, and, to a minor extent, through the gills, the SJNNV strain seems to enter fish only through the gills and the RGNNV strain could use all tissues indistinctly. Taken together, all these results support the hypothesis that reassortment has improved betanodavirus infectivity for sole.

Betanodavirus and VER Disease: A 30-year Research Review

“…Similarly, interspecies horizontal transmission has been observed between European sea bass and gilthead sea bream reared on the same farm [129] and in experimental trials between turbot and Atlantic cod [195] and between Asian seabass and brown-marbled grouper [194]. Viral shedding from gills and skin could be involved in this transmission, as reported in Senegalese sole [159]. The main factors affecting horizontal transmission in farming conditions are stocking density [196], and temperature [148,149].…”

“…Several portals of viral entry have been suggested, including epithelial cells covering the fish body and/or the fin [159], gills [159][160][161] and nasal and oral cavity [158][159][160]162].…”

“…Analyses of experimentally infected Atlantic cod suggest an initial viremia followed by neural spread [180]. Although in most cases NNV detection in non-neurologicaltissues has been performed using histological or molecular techniques, the presence of infective particles has been confirmed in gills, skin, fins and intestine of Senegalese sole [159] and testis of European sea bass and gilthead sea bream [187].…”

“…The dynamics of NNV infections seem to be fast; the RGNNV genome was detected in the brain of infected pompano at 4 hpi [188] and both genome and infective particles of a reassortant RGNNV/SJNNV strain were detected after 1 day post infection (dpi) in the brain of Senegalese sole [159]. However, differences related to genotypes and fish species can be observed because in Senegalese sole the RGNNV genome was not detected until 3 dpi, and the detection of infective particles took one more day (4 dpi) [159]. This fast replication also implies the fast development of disease signs in infected fish, which were observed as early as 2 dpi in intramuscularly injected juvenile European sea bass and bath infected Asian sea bass larvae [160,189].…”

“…Gonads have been demonstrated to be involved in viral shedding in striped jack, European sea bass and gilthead sea bream [182,187,203,205]. In striped jack and Senegalese sole, the intestine has also been reported to take part in viral release [159,182] which would result in the contamination of eggs [182].…”