Certainly infected fish are able to spread the pathogen to other aquatic

Certainly infected fish are able to spread the

This preview shows page 268 - 269 out of 594 pages.

the fish host. Certainly, infected fish are able to spread the pathogen to other aquatic invertebrates. Thus, when Arctic charr (Salvelinus alpinus) were challenged intra- peritoneally and the fish began to die, the pathogen spread to and could be cultured from the freshwater bivalve Amblema plicata, which were placed in the experimental system. Fish added to the system with the infected Amblema plicata after 1 and 5, but not after 15, days succumbed to infection and died (Starliper, 2001a). The site(s) of entry into the fish also remain uncertain. All of these questions must be answered before the gaps in the understanding of the epizootiology of diseases of Aer. salmonicida aetiology can be filled. Unfortunately, epizootiological studies have not been aided by modern scientific approaches, such as plasmid-profiling (Austin et al, 1998) or ribotyping (Nielsen et al, 1994). The ecology of Aeromonas salmonicida McCarthy (1980) performed detailed experiments concerned with the ecology o^ Aer. salmonicida and also reviewed the work carried out by others. According to his report, contact with infected fish or contaminated water and fish farm materials, and transovarian transmission have all been cited as probable routes of infection. Also, carrier fish, which show no overt signs of disease but harbour the pathogen in their tissues, appear to be implicated in horizontal or vertical transmission. Such carrier fish are presumed to provide a reservoir which retains the pathogen in fish populations. Sea lamprey have been found to harbour typical Aer. salmonicida, and it may well be that this fish species is a possible source of infection for salmonids (El Morabit et al., 2004). To understand how Aer. salmonicida is transmitted both among and within fish populations it is necessary to know the source of the pathogen and its capacity to survive in the environment. In fact, most of the work done on epizootiological aspects of fish diseases caused by Aer. salmonicida has focused on investigations of potential sources of infection. The role of water, mud and detritus, contaminated implements on fish farms, animals other than fish themselves, and, particularly, carrier fish (i.e. salmonids as well as non-salmonids) as potential sources of infection with Aer. salmonicida have been examined. The popular approach to the study of this subject has been to determine the presence of and survival capabilities of Aer. sal- monicida in the variety of habitats listed above. Certainly, there is evidence that the pathogen can survive without a significant change in numbers in transport systems, such as containing Stuart's medium, at 18-20°C for 48 h (Cipriano and Bullock, 2001). This opens up the possibiHty of transporting samples from field to laboratory without greatly influencing the populations of Aer. salmonicida.
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