Section of Animal and Veterinary Sciences, Department of Agricultural, Food, Environmental and Animal Sciences (DI4A), University of Udine, Udine, Italy.
Department of Fish Health Management, Faculty of Fisheries, Sylhet Agricultural University, Sylhet, Bangladesh.
J Fish Dis. 2023 Jul;46(7):731-741. doi: 10.1111/jfd.13782. Epub 2023 Mar 21.
Lactococcosis, caused by the Gram-positive bacterium Lactococcus garvieae, is a major concern in rainbow trout (Oncorhynchus mykiss) farms, which are regularly affected by outbreaks especially during the summer/fall months. In these farms, unvaccinated healthy and symptomatic fish can coexist with vaccinated fish. In the present study, innate (leukogram, serum lysozyme activity, peroxidase activity, antiprotease activity, bactericidal activity, total IgM and total proteins), and specific immune parameters (serum antibodies to L. garvieae) were assessed in unvaccinated adult rainbow trout naturally exposed to the pathogen, with or without evidence of clinical signs, or subjected to vaccination. Blood was drawn from all three groups, and blood smears were prepared. Bacteria were found in the blood smears of 70% of the symptomatic fish but not in any of the asymptomatic fish. Symptomatic fish showed lower blood lymphocytes and higher thrombocytes than asymptomatic fish (p ≤ .05). Serum lysozyme and bactericidal activity did not vary substantially among groups; however, serum antiprotease and peroxidase activity were significantly lower in the unvaccinated symptomatic group than in the unvaccinated and vaccinated asymptomatic groups (p ≤ .05). Serum total proteins and total immunoglobulin (IgM) levels in vaccinated asymptomatic rainbow trout were significantly higher than in unvaccinated asymptomatic and symptomatic groups (p ≤ .05). Similarly, vaccinated asymptomatic fish produced more specific IgM against L. garvieae than unvaccinated asymptomatic and symptomatic fish (p ≤ .05). This preliminary study provides basic knowledge on the immunological relationship occurring between the rainbow trout and L. garvieae, potentially predicting health outcomes. The approach we proposed could facilitate infield diagnostics, and several non-specific immunological markers could serve as reliable indicators of the trout's innate ability to fight infection.
乳球菌病是由革兰氏阳性细菌乳球菌引起的，是虹鳟（Oncorhynchus mykiss）养殖场的主要关注点，这些养殖场经常受到疫情的影响，尤其是在夏季/秋季。在这些养殖场中，未接种疫苗的健康和有症状的鱼与接种疫苗的鱼可以共存。在本研究中，评估了未接种疫苗的成年虹鳟在自然暴露于病原体时的固有（白细胞计数、血清溶菌酶活性、过氧化物酶活性、抗蛋白酶活性、杀菌活性、总 IgM 和总蛋白）和特异性免疫参数（对 L. garvieae 的血清抗体），无论是否有临床症状，或接种疫苗。从所有三组鱼中抽取血液并制备血涂片。在 70%的有症状鱼的血涂片中发现了细菌，但在无症状鱼中未发现细菌。有症状的鱼的血液淋巴细胞比无症状的鱼少，而血小板比无症状的鱼多（p ≤.05）。血清溶菌酶和杀菌活性在各组之间没有显著差异；然而，未接种疫苗的有症状组的血清抗蛋白酶和过氧化物酶活性明显低于未接种疫苗和接种疫苗的无症状组（p ≤.05）。接种疫苗的无症状虹鳟的血清总蛋白和总免疫球蛋白（IgM）水平明显高于未接种疫苗的无症状和有症状组（p ≤.05）。同样，接种疫苗的无症状鱼产生的针对 L. garvieae 的特异性 IgM 也明显高于未接种疫苗的无症状和有症状鱼（p ≤.05）。这项初步研究提供了虹鳟与 L. garvieae 之间发生的免疫关系的基本知识，可能预测健康结果。我们提出的方法可以促进现场诊断，并且几种非特异性免疫标志物可以作为虹鳟抵抗感染的固有能力的可靠指标。
