Establishment of an Asymptomatic Carrier State Infection of Enteric Redmouth Disease in Rainbow Trout (Salmo gairdneri)

Abstract

The dynamics of establishment, pathogenesis, and continued maintenance of Enteric Redmouth (ERM) disease in rainbow trout (Salmo gairdneri) were examined. Groups were infected by parenteral and oral routes and subsampled at weekly intervals. Both modes of infection were standardized to obtain ID100 levels of infection with an average of 30 bacteria constituting an LD50 dosage when administered parenterally. The clinical course of the disease was monitored up to 102 days postinfection. A clinically asymptomatic carrier state infection was established in the lower intestine of 25% of survivors 45 days postinfection at 14.5 C. Thereafter, regular intestinal shedding of the pathogen, causing recurrent infection and mortality within the population, occurred on acyclic basis of 30–40-day intervals. Clinical recovery, establishment of the asymptomatic condition, and periodicity of intestinal shedding and the clinical course of the disease to convalescence were described.

Route of entry and tissue distribution of Yersinia ruckeri in experimentally infected rainbow trout Oncorhynchus mykiss

“…Although the gills are apparently an important portal of entry for Yersinia ruckeri, the bacterium may also successfully colonize other body surfaces and gain entry to the body by a variety of routes, including the skin and the gut, as suggested by Busch & Lingg (1975) and Valtonen et al (1992). In our study, moderate numbers of Y. ruckeri were isolated from the skin and gut immediately after infection.…”

Enteric redmouth disease: outbreak in rainbow trout in Switzerland

“…However, the source of the pathogen is still uncertain. It is generally agreed that ERM may become established in new areas following its introduction with camer-fish (Rucker 1966, Wobeser 1973, Busch & Lingg 1975. However, there is also evidence that Y. ruckeri is widely distributed and that fish-mediated transmission may not always account for its distribution (Bullock et al 1978).…”

“…The latter have been routinely examined since 1981 but so far, no ERM has been detected in either of them. Notwithstandng this, because the frequency of ERM camer-fish is generally rather low (Busch & Lingg 1975) one cannot exclude the possibility that the infection was introduced into the affected farm by camers from the German farm. The Yersinia ruckeri affected farm, established 5yr ago, uses only spring water and therefore camer fish do not occur in its water supply.…”

Interactions of virulent and avirulent Yersinia ruckeri strains with isolated gill arches and intestinal explants of rainbow trout Oncorhynchus mykiss

“…Basic steps in the establishment of an infection include attachment to the epithelium followed by invasion at the portal of entry. Both the gills and intestinal tract have been suggested as possible routes of entry for Y. ruckeri (Busch & Lingg 1975, Valtonen et al 1992, Tobback et al 2009). Therefore, the interactions of Y. ruckeri with the gills and the gut were studied using standardized perfusion models.…”