|Haig, Sarah -|
|Davies, Robert -|
|Reese, Allan -|
|Verner-Jefferies, David -|
Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 23, 2010
Publication Date: August 1, 2010
Citation: Haig, S., Davies, R.L., Welch, T.J., Reese, A.R., Verner-Jefferies, D. 2010. Comparative susceptibility of Atlantic salmon and rainbow trout to Yersinia ruckeri: relationship to O antigen serotype and resistance to serum killing. Veterinary Microbiology. doi:10.1016/j.vetmic.2010.06.022 Interpretive Summary: Infectious diseases are a major impediment to efficient aquatic animal production and cause significant economic losses. To develop improved strategies for disease control a better understanding of the host-pathogen interactions leading to the diseases state are needed. Yersinia ruckeri, a Gram negative enterobacterium, is the causative agent of enteric redmouth (ERM) disease, a chronic to acute haemorrhagic septicaemia of salmonid fish species. ERM primarily affects cultured rainbow trout but increasingly has caused disease outbreaks in Atlantic salmon. We compared the virulence and serum resistance properties of Atlantic salmon and rainbow trout Yersinia ruckeri isolates, confirming hatchery reports that Y. ruckeri poses a significant risk to salmon, as well as to rainbow trout. Strains that affect salmon show a wider diversity in their phenotypic characters compared to ERM-causing serotype O1 rainbow trout isolates suggesting that certain strains of this pathogen may be better suited to infect salmon (host tropism).
Technical Abstract: A study was undertaken to compare the virulence and serum killing resistance properties of Atlantic salmon and rainbow trout Yersinia ruckeri isolates. Five isolates, covering heat-stable O-antigen O1, O2 and O5 serotypes, were tested for virulence towards fry and juveniles of both species by experimental bath challenge. The sensitivity of 15 diverse isolates to non-immune salmon and rainbow trout serum was also examined. All five isolates caused significant mortality in salmon fry. Serotype O1 isolate 06059 caused the highest mortality in salmon (74% and 70% in fry and juveniles respectively). Isolate 06041, a typical ERM-causing serotype O1 UK rainbow trout strain, caused mortalities in both rainbow trout and salmon. None of the salmon isolates caused any mortalities in 150-250g rainbow trout, and only serotype O2 isolate 06060 caused any significant mortality (10%) in rainbow trout fry. Disease progression and severity was affected by water temperature. Mortality in salmon caused by the isolates 06059 and 05094 was much higher at 16 oC (74 and 33%, respectively) than at 12 deg C (30 and 4% respectively). Virulent rainbow trout isolates were generally resistant to sera from both species, whereas salmon isolates varied in their serum sensitivity. Convalescent serum from salmon and rainbow trout that had been infected by serotype O1 isolates mediated effective classical pathway complement killing of serotype O1 and O5 isolates that were resistant to normal sera. Overall, strains recovered from infected salmon possess a wider range of phenotypic properties (relative virulence, O serotype and possession of serum-resistance factors), compared to ERM-causing rainbow trout isolates.