regarded as essential for the association with the host surface OToole et ai

Regarded as essential for the association with the

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regarded as essential for the association with the host surface (O'Toole et ai, 2004). Home and Baxendale (1983) reported adhesion of V. anguillarum to intestinal sections derived from rainbow trout. All regions of the intestine were colonised (approximately 10^ cells/cm^), with maximum attachment occurring within 100 min. It is interesting to note that serogroup Ol, but not 02, isolates demonstrated the ability to adhere to mucus from Atlantic salmon epithelial surfaces, i.e. foregut, gills, hindgut, pyloric caeca and skin (Knudsen et ai, 1999). Orally administered V. anguillarum survived in the stomach of juvenile turbot for several hours, persisted in the intestine and proliferated in faeces (Olsson et ai, 1998). This view has been reinforced by a study, which concluded that >50% of the spleens of turbot contained cells of V. anguillarum after infection via the oral and rectal routes (Olsson et ai, 1996). The skin appears to become colonised within 12 h of immersion in a virulent culture (Kanno et ai, 1990). Then, invasion of the liver, spleen, muscle, gills and intestine follows (Muroga and De La Cruz, 1987). Resistance to the potential debilitating effect offish serum (Trust et ai, 1981) may hasten the invasion processes. Some degree of host specificity has been indicated, insofar as strains from rainbow trout were poorly pathogenic to saithe, and vice versa (Egidius and Andersen, 1978). This raises the question concerning the size of inoculum necessary to achieve clinical disease. Levine et al. (1972) reported lesions at the site of infection in winter flounder after exposure to only 640 cells. These were administered by intradermal injection. Much larger inocula resulted in sizeable mortahties. For example, Evelyn (1971b) determined that Oncorhynchus keta and O. nerka died within 48 h of receiving, by i.p. injection, 0.1ml containing 10^ viable cells of V. anguillarum. In a much more spectacular demonstration of virulence. Sawyer et al. (1979) established 80-100% mortality in a population of Atlantic salmon following exposure to 1-2.5 x 10^ cells/ ml as a bath for 1 h. In this demonstration, the fish were maintained at a water temperature of 10-15°C. However, temperature shocking does exacerbate mortality. Thus, in one series of experiments using rainbow trout, the temperature was decreased from 23 to 10°C resulting in a significantly increased level of mortality, an increase which was not correlated with an impairment in immune parameters (Aoshima et al, 2005). Turbot larvae have been successfully challenged with V. anguillarum orally via live feed (Grisez et al, 1996; Planas et al, 2005). Using 10^ Artemia nauplii/ml and 10^ F. anguillarum cells/ml, the recipient fish died within 4 days (Grisez et al, 1996). Similarly, feeding with rotifers containing V. anguillarum cells led to a successful infection of turbot larvae (Planas et al., 2005).
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