2013 Annual Report
1a.Objectives (from AD-416):
Determine the influence of external parasitic infestation on innate resistance in fish to bacterial infection and disease and the effect on the acquired immune responses to bacterial infection and disease on fish vaccination.
1b.Approach (from AD-416):
Tilapia, catfish, pintado, pacu and other species of warmwater fish will be used to determine the effect of external parasitic infestation by Gyrodactylidae and Dactylogyridae monogeneans, trichodinids and/or Ichthyophthirius multifiliis on the innate immune responses to Streptococcus (S.) iniae, S. agalactiae and Aeromonas (A.) hydrophila under experimental infection and disease. The effect of these parasites on the protective acquired immune response to S. iniae, S. agalactiae, and A. hydrophila infection and disease will also be determined on fish vaccination against these bacterial pathogens. The techniques employed include those from the areas of parasitology, bacteriology, immunology, histology and molecular biology to quantitatively measure parasite and bacteria infectivity, pathology, ELISA antibody responses and molecular responses of immune and related genes in parasitized fish subjected to bacterial infections. The data will be subjected to statistical analysis.
Two important diseases of catfish aquaculture are enteric septicemia of catfish (ESC) caused by bacteria Edwardsiella (E.) ictaluri and protozoan parasite Ichthyophthirius (Ich). These two pathogens commonly coexist in the aquaculture environment and limited information is available on the effect that coinfection has on catfish health. ARS scientists at Auburn, Alabama, in collaboration with a visiting scientist from Santa Catarina, Brazil, conducted a study to evaluate the effect of parasitism by Ich on survival, blood cell parameters and bacterial load in catfish previously exposed to E. ictaluri. Parasitism of fish previously exposed to E. ictaluri resulted in increased mortality and changes in hematological parameters. Bacterial load remained elevated in the co-infected fish for a longer period, while bacteria only exposed fish cleared the infection more quickly. The study results provide fish farmers and hatchery managers the potential negative effect of multiple pathogen coinfections that result in high mortality and potential economic loss.