These new outbreaks also caused great consternation due not only to a decline

These new outbreaks also caused great consternation

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These new outbreaks also caused great consternation, due not only to a decline in fish numbers, especially valuable breeding stock, but also to loss of revenue from fishing rights (Lund, 1967). There seemed to be no doubt that the disease had become enzootic in Great Britain. In North America the first report of furunculosis was made by Marsh (1902) who described an organism, which was named as Bacillus truttae. This caused an epizootic in hatchery fish in Michigan. Later, Belding (1927) reported the loss of an entire stock of brook trout due to furunculosis at the Massachusetts State Hatchery. Davis (1929) contended that serious mortality had been restricted to brown and brook trout in hatcheries and rearing ponds. However, the extent of the problem was reflected in the calculations of Smith (1942), who reckoned that the disease had occurred in more than 25% of the hatcheries in the U.S.A. However, as in Great Britain, furunculosis in North America was eventually shown to be not solely a hatchery disease; a study by Fish (1937) revealed the presence of Aer. salmonicida in wild stock of adult Loch Leven trout (Salmo trutta levensis) in Wyoming. In Canada, Duff and Stewart (1933) investigated disease outbreaks among salmonids in British Columbia. Several fish species, such as wild Rocky Mountain whitefish (Prosopium williamsoni), Dolly Varden (Salvelinus marme Walbaum) and cutthroat trout (Salmo clarki), were reported in 1929 and 1930 to be dying from a disease, a major symptom of which was the appearance of red "bUsters" on the body. In 1931, Bacillus salmonicida was isolated from diseased specimens. Nevertheless, despite the occurrence of furuncu- losis in wild stock in North America, it does not appear to have assumed epizootic status in rivers. At present, the geographical distribution of the pathogen is worldwide, including AustraHa (Trust et ai, 1980b) and the mainland of Asia, i.e. Korea (Fryer et ai, 1988) where it was formerly believed to be absent. The pattern formed by the locations from where the disease has occurred since the initial report of Emmerich and Weibel (1894) suggests that it spread from a focal point in Europe. However, according to McCarthy and Roberts (1980), this may reflect progress in bacteriological diagnostic facihties as well as an actual dissemination of the pathogen. Investigations into the epizootiology of Aer. salmonicida have not provided unequivocal answers for several crucial questions concerning the factors which con- trol or determine the dissemination of the pathogen. Although Aer. salmonicida has been recognised for ~100 years, the precise route of transmission has not been conclusively resolved. Some studies indicate that the pathogen is widespread among wild salmonids. For example, in a study using DNA probe technology of the blood from 61 fish caught from 3 rivers in Ireland, Mooney et al. (1995) reported
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248 Bacterial Fish Pathogens a widespread, low-level infection. Controversy persists as to whether or not the organism is capable of a free-living existence in the natural environment, away from the fish host. Certainly, infected fish are able to spread the pathogen to other aquatic
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  • Bacteria, representative, gram-negative bacteria

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