Immune profiling of rainbow trout (Oncorhynchus mykiss) exposed to Lactococcus garvieae: Evidence in asymptomatic versus symptomatic or vaccinated fish
Investigation published in Journal of Fish Diseases
July 1st, 2023
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
Ibrahim Khalil SM., Bulfon C., Galeotti M., Acutis PL., Altinok I., Kotzamanidis C., Vela AI., Fariano L., Prearo M., Colussi S. and Volpatti D.
| Section of Animal and Veterinary Sciences. Department of Agricultural, Food, Environmental and Animal Sciences. Università degli Studi di Udine (UNIUD). | |
| Department of Fish Health Management. Faculty of Fisheries. Sylhet Agricultural University. | |
| Istituto Zooprofilattico Sperimentale del Piemonte (IZSTO). | |
| Aquatic Animal Health and Molecular Genetic Lab. Department of Fisheries Technology Engineering. Karadeniz Technical University (KTU). | |
 | Servicio de Identificación y Caracterización Microbiana (ICM). Centro de Vigilancia Sanitaria Veterinaria (VISAVET). Universidad Complutense (UCM). |
| Departamento de Sanidad Animal. Facultad de Veterinaria. Universidad Complutense (UCM). |
| Elgo-Dimitra Thessaloniki. | |
