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Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Title: Parasites can enhance infections of fish with bacterial pathogens

item Xu, Dehai
item Shoemaker, Craig

Submitted to: International Aquaculture Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/19/2015
Publication Date: 8/31/2015
Citation: Xu, D., Shoemaker, C.A. 2015. Parasites can enhance infections of fish with bacterial pathogens. In: 9th International Symposium on Fish Parasites, August 31-September 4, 2015, Valencia, Spain. p. 34.

Interpretive Summary:

Technical Abstract: In aquaculture systems, fish are commonly infected by multiple pathogens, including parasites. Parasite Ichthyophthirius multifiliis (Ich) and bacterium Edwardsiella ictaluri are two common pathogens of cultured channel catfish. The objectives were to 1) evaluate the susceptibility of Ich parasitized catfish to E. ictaluri, 2) quantify bacterial loads using quantitative real-time polymerase chain reaction (qPCR) in fish tissues after parasitism by Ich; and 3) determine whether Ich could vector E. ictaluri to catfish. Fluorescent tagged bacterium E. ictaluri was used to assess the ability of Ich to vector E. ictaluri. Ich-parasitized catfish showed significantly higher mortality (91.7%) when exposed to E. ictaluri than non-parasitized fish (10%). Bacterial loads in fish infected by Ich theronts was 40 and 2000 fold higher than non-parasitized fish. Ich theronts showed significantly higher fluorescing bacteria (23-39 %) than control theronts (~6 %) after exposure to fluorescent E. ictaluri. Edwardsiella ictaluri survived and replicated during tomont division. Sixty percent of fish exposed to theronts treated with E. ictaluri were positive for E. ictaluri by fluorescent microscopy. Fluorescent E. ictaluri were observed in skin and gill tissue of dead fish. This study demonstrated that Ich infection resulted in enhanced bacterial invasion, increased fish mortality, and Ich vectored E. ictaluri into catfish. Prevention of parasite infection in fish may reduce fish mortality due to bacterial co-infection. The work also highlights the potential role of parasites in vectoring bacterial pathogens. Movement or purchase of new fish should take into account the potential for concomitantly introducing multiple microbial disease agents.