Disease Resistance in Atlantic Salmon (Salmo salar): Coinfection of the Intracellular Bacterial Pathogen Piscirickettsia salmonis and the Sea Louse Caligus rogercresseyi

Abstract

BackgroundNaturally occurring coinfections of pathogens have been reported in salmonids, but their consequences on disease resistance are unclear. We hypothesized that 1) coinfection of Caligus rogercresseyi reduces the resistance of Atlantic salmon to Piscirickettsia salmonis; and 2) coinfection resistance is a heritable trait that does not correlate with resistance to a single infection.MethodologyIn total, 1,634 pedigreed Atlantic salmon were exposed to a single infection (SI) of P. salmonis (primary pathogen) or coinfection with C. rogercresseyi (secondary pathogen). Low and high level of coinfection were evaluated (LC = 44 copepodites per fish; HC = 88 copepodites per fish). Survival and quantitative genetic analyses were performed to determine the resistance to the single infection and coinfections.Main Findings C. rogercresseyi significantly increased the mortality in fish infected with P. salmonis (SI mortality = 251/545; LC mortality = 544/544 and HC mortality = 545/545). Heritability estimates for resistance to P. salmonis were similar and of medium magnitude in all treatments (h 2 SI = 0.23±0.07; h 2 LC = 0.17±0.08; h 2 HC = 0.24±0.07). A large and significant genetic correlation with regard to resistance was observed between coinfection treatments (rg LC-HC = 0.99±0.01) but not between the single and coinfection treatments (rg SI-LC = −0.14±0.33; rg SI-HC = 0.32±0.34).Conclusions/Significance C. rogercresseyi, as a secondary pathogen, reduces the resistance of Atlantic salmon to the pathogen P. salmonis. Resistance to coinfection of Piscirickettsia salmonis and Caligus rogercresseyi in Atlantic salmon is a heritable trait. The absence of a genetic correlation between resistance to a single infection and resistance to coinfection indicates that different genes control these processes. Coinfection of different pathogens and resistance to coinfection needs to be considered in future research on salmon farming, selective breeding and conservation.

Half a century of genetic interaction between farmed and wild Atlantic salmon: Status of knowledge and unanswered questions

“…For example in Atlantic Canada, only the St. John River domesticated strain (Friars, Bailey, & Oflynn, ; Quinton, McMillan, & Glebe, ; Wolters, Barrows, Burr, & Hardy, ) is permitted for use in commercial aquaculture, while in Scotland, some local‐based strains, for example Landcatch, are also being used in addition to Norwegian strains (Powell, White, Guy, & Brotherstone, ; Tsai, Hamilton, Guy et al., ). Other strains under selection are also in existence in other countries, such as Tasmania, Australia (Taylor, Kube, Muller, & Elliott, ; Taylor, Wynne, Kube, & Elliott, ) and Chile (Lhorente, Gallardo, Villanueva, Carabano, & Neira, ; Yanez et al., ).…”

Parasitism perturbs the mucosal microbiome of Atlantic Salmon

“…Prostaglandin E, Trypsin), that down-regulate T-cell and other functions required to effectively cope with bacterial pathogens1314. Experimental S. salar co-infections between a Chilean copepod species Caligus rogercresseyi and the bacteria P. salmonis show that survival rates in the co-infected fish (0% after 53 days) are substantially lower than in fish infected with P. salmonis alone (c.57% over the same period)11. Whilst there is an increasing understanding of salmonid immunity to copepod pathogens, as well as to secondary agents, nothing is known about the role commensal microbes may play in such infections.…”

Advances in genetic improvement for salmon and trout aquaculture: the Chilean situation and prospects

“…) or coinfection of different pathogens (Lhorente et al . ), have also been studied; however, further studies are needed in order to evaluate a broader range of environmental factors and pathogens. This information will help to establish effective disease control plans using fish genetically improved for disease resistance.…”