ARS | Publication request: Effect of parasitism on vaccine efficacy against Streptococcus iniae in Nile tilapia

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 19, 2011
Publication Date: January 27, 2011
Repository URL: http://handle.nal.usda.gov/10113/55529
Citation: Martins, M.L., Shoemaker, C.A., Xu, D., Klesius, P.H. 2011. Effect of parasitism on vaccine efficacy against Streptococcus iniae in Nile tilapia. Aquaculture. 314:18-23.

Interpretive Summary: Trichodina, Ichthyophthirius (Ich) and Gyrodactylus are important ectoparasites that affect cultured fish all over the world. The parasites cause fish tissue damage and consequently lead to economical losses in aquaculture. Vaccines against fish pathogens are an alternative to indiscriminate use of antibiotics in aquaculture. There is no information on the effects of parasitism on the vaccine efficacy for cultured fish. This study determined whether parasitism by Trichodina, Gyrodactylus and Ich influenced vaccine efficacy against Streptococcus iniae (a gram positive bacteria) in Nile tilapia. Antibody level, hematology and survival of fish vaccinated with a modified S. iniae bacterin were compared among non-parasitized fish, fish infected by Trichodina and Gyrodactylus, and fish infected by three parasites. The study results demonstrated a reduction in vaccine performance in fish parasitized by three parasites compared to non-parasitized fish. A decrease in antibody levels, red blood cell and white blood cell counts were also observed in the parasitized vaccinated fish. This study highlights the importance of monitoring or controlling parasite levels in the aquaculture setting to optimize vaccine efficacy.

Technical Abstract: Limited information is available on vaccine performance in parasitized fish. The objective of this study was to determine if parasitism of fish affected vaccine efficacy. Antibody level, hematology and survival of Nile tilapia vaccinated with a modified S. iniae bacterin were compared among non-parasitized fish, fish parasitized by Trichodina heterodentata and Gyrodactylus cichlidarum, and fish parasitized by T. heterodentata, G. cichlidarum and Ichthyophthyrius multifiliis (Ich). Among vaccinated fish, fish free from parasites (Trichodina, Gyrodactylus and Ich) had the highest antibody level (0.43, SE=0.32). Significantly (p<0.05) lower anti-S. iniae antibody was noted in parasitized vaccinated fish (0.30, SE=0.19). Among the vaccinated treatments, fish parasitized by Trichodina, Gyrodactylus and Ich showed the lowest survival (80.0 %, SE=14.1), significantly (p<0.05) lower than vaccinated fish free from parasites (97.5 %, SE=3.5) or parasitized by Trichodina and Gyrodactylus (95.0%, SE=7.1). Following challenge with S. iniae, non-vaccinated fish free from parasites showed higher survival (47.5%, SE=3.5) than non-vaccinated fish parasitized by Trichodina and Gyrodactylus (37.5%, SE=3.5). Non-vaccinated fish parasitized by all 3 parasites showed the lowest survival (27.5 %, SE=3.5) post challenge. Relative percent survival (RPS) demonstrated a decrease in vaccine performance for the group of fish that were parasitized with Trichodina and Gyrodactylus and Ich. RPS was 72 % compared to 95 and 92%, respectively, in the other vaccinated treatments following challenge. This study demonstrated a reduction in vaccine performance in parasitized tilapia and highlights the importance of monitoring or controlling parasite levels in the aquaculture setting to optimize vaccine efficacy.