Triploid atlantic salmon (Salmo salar L.) post-smolts accumulate prevalence more slowly than diploid salmon following bath challenge with salmonid alphavirus subtype 3

Abstract

Triploid Atlantic salmon (Salmo salar L.) may play an important role in the sustainable expansion of the Norwegian aquaculture industry. Therefore, the susceptibility of triploid salmon to common infections such as salmonid alphavirus (SAV), the causative agent of pancreas disease (PD), requires investigation. In this study, shortly after seawater transfer, diploid and triploid post-smolts were exposed to SAV type 3 (SAV3) using a bath challenge model where the infectious dose was 48 TCID50 ml-1 of tank water. Copy number analysis of SAV3 RNA in heart tissue showed that there was no difference in viral loads between the diploids and triploids. Prevalence reached 100% by the end of the 35-day experimental period in both infected groups. However, prevalence accumulated more slowly in the triploid group reaching 19% and 56% at 14 and 21 days post exposure (dpe) respectively. Whereas prevalence in the diploid group was 82% and 100% at the same time points indicating some differences between diploid and triploid fish. Both heart and pancreas from infected groups at 14 dpe showed typical histopathological changes associated with pancreas disease. Observation of this slower accumulation of prevalence following a natural infection route was possible due to the early sampling points and the exposure to a relatively low dose of virus. The triploid salmon in this study were not more susceptible to SAV3 than diploid salmon indicating that they could be used commercially to reduce the environmental impact of escaped farmed fish interbreeding with wild salmon. This is important information regarding the future use of triploid fish in large scale aquaculture where SAV3 is a financial threat to increased production.

Time after seawater transfer influences immune cell abundance and responses to SAV3 infection in Atlantic salmon

“…The test was two-sided, and the significant level was set to In the following sections, the results for control fish are presented first, facilitating a comparison of the results from the infected fish. These results build on the knowledge gathered from previously published data on the susceptibility of these groups of fish to SAV3 at these time-points after seawater transfer and on their immune responses(Jarungsriapisit, Moore, Taranger, et al, 2016;Moore, Jarungsriapisit, et al, 2017;Moore et al, 2018) by examining the types of immune cells present in the target tissues for this SAV3 infection.…”

“…with either 10 4 TCID 50 SAV3 This is based on testing of different doses in the dose range over time while studying infection dynamics with SAV3 in our laboratory over several years, and in particular in two previously published studies. In these earlier studies, both a five times difference in dose (Jarungsriapisit, Moore, Maehle, et al, 2016) and larger fish with a reduced dose (Moore, Nilsen, et al, 2017) had no impact on the progression of histopathological changes, and thus, we could directly compare the two phases. Fish were anaesthetized using both a sedative, 10 mg/l metomidate, and an anaesthetic, 60 mg/l benzocaine, before handling and euthanized with 10 mg/l metomidate and 160 mg/l of Benzocaine before sampling.…”

“…Innate immune gene transcription including interferon, viperin, TLR7, TLR8a1, MyD88 and IRF7 has been reported to be downregulated in recently transferred smolts compared with smolts adapted to seawater for a longer period . In addition, the immune response in these recently transferred smolts was both reduced and transient compared with salmon adapted to seawater for a longer time (Moore, Jarungsriapisit, et al, 2017;Moore et al, 2018). This, to some extent, may explain why Atlantic salmon at 2 wpt are more susceptible to SAV3 infection than post-smolts at 9 wpt (Jarungsriapisit, Moore, Taranger, et al, 2016).…”

“…Innate and adaptive immune systems play an important and interdependent role in antiviral defence mechanisms. Several important immune response cascades are activated at a both transcriptional and translational level (Braceland et al, 2013;Graham, Rowley, & Frost, 2014;Grove et al, 2013;Herath et al, 2012;Moore, Jarungsriapisit, et al, 2017). Cells such as neutrophils/granulocytes, macrophages, dendritic cells, natural killer cells, B and T cells respond to pathogen invasion and are important during the initial response and further activation of the adaptive immune system.…”

Transcriptional profiling and biomarker identification reveal tissue specific effects of expanded ataxin-3 in a spinocerebellar ataxia type 3 mouse model

“…We observed larger fold changes and more differentially expressed genes in striatum and brainstem than observed in cortex and cerebellum. As we and others have repeatedly shown similar expression of the mutant ataxin-3 transgene in the MJD84.2 mouse model in the brain regions tested here [ 16 , 73 , 74 ], it is unlikely that variations in expression levels can explain these differences. Since previous studies suggest that cellular ATXN3 transcript and protein levels do not correlate well with neuronal degeneration in SCA3 [ 39 , 75 ], these findings are indicative of differential effects of mutant ataxin-3 in each brain region.…”