This study was promoted following concern over increasing mortality on 2 farms rearing Atlantic salmon Salmo salar in the Shetland Isles, Scotland. A Mycobacterium sp. was isolated from monbund, market-s~zed Atlantic salmon. Biochemical tests, 1ipi.d analys~s and PCR (polynlerase chain reaction) techniques confirmed the bacterium to be Mycobacterium chelonae. Multiple greyish-white miliary granuloma-like nodules were observed in several tissues. Dense hard-packed nodules contained abundant acid-fast bacteria. Atlantic salmon injected with M. chelonae remained sub-clinically infected, demonstrating the chronic nature of this disease. The source of the pathogen was not identified.

Grey mullet, Chelon labrosur, (60-IOOg) have been found to respond immunologically to Crypfocofyle lingua, following a single exposure to 20000 cercariae, by the production of humoral antibody, sensitized pronephric leucocytes and cytotoxic serum factors. Antibody titres measured by passive haemagglutination reached a peak at week 4 with a -log, titre of 16 f SE. 1 .O, and titres of 10.7 f S.E I .O were still recorded after 10 weeks at the termination of the experiment. Cercarial agglutination was found unreliable as a rapid test. Pronephric leucocytes, sensitive to cercarial antigen when measured by the under-agarose migration method, were detected between weeks 1 and 6, peaking at week 2. In v i m polarization was increased when cells were incubated with the antigen, but this increase was not significantly different between control and infected fish. Heat-labile cytotoxic factors of immune sera have been demonstrated to whole cercariae in vifro, these factors being associated with structural damage to the tegument. Pronephros cells isolated from immune fish during each week of infection showed no evidence of adherence to cercariae or metacercariae in vitro. The results are discussed in relation to both host response and course of infection of the parasite.

No abstract

No abstract