In vitro toxicity of bithionol and bithionol sulphoxide to Neoparamoeba spp., the causative agent of amoebic gill disease (AGD)

Abstract

The objective of the present study was to evaluate the in vitro toxicity of bithionol and bithionol sulphoxide to Neoparamoeba spp., the causative agent of amoebic gill disease (AGD). The current treatment for AGD-affected Atlantic salmon involves bathing sea-caged fish in freshwater for a minimum of 3 h, a labour-intensive and costly exercise. Previous attempts to identify alternative treatments have suggested bithionol as an alternate therapeutic, but extensive in vitro efficacy testing has not yet been done. In vitro toxicity to Neoparamoeba spp. was examined using amoebae isolated from the gill of AGD-affected Atlantic salmon and exposing the parasites to freshwater, alumina (10 mg l -1 ), seawater, bithionol or bithionol sulphoxide at nominal concentrations of 0.1, 0.5, 1, 5 and 10 mg l -1 in seawater. The numbers of viable amoebae were counted using the trypan blue exclusion method at 0, 24, 48 and 72 h. Both bithionol and bithionol sulphoxide demonstrated in vitro toxicity to Neoparamoeba spp. at all concentrations examined (0.1 to 10 mg l -1 over 72 h), with a comparable toxicity to freshwater observed for both chemicals at concentrations > 5 mg l -1 following a 72 h treatment. Freshwater remained the most effective treatment, with only 6% viable amoebae seen after 24 h and no viable amoebae observed after 48 h. KEY WORDS: Amoebic gill disease · AGD · Bithionol · In vitro · Toxicity · Neoparamoeba spp. · Atlantic salmon · Chemotherapy · Protozoan parasite Resale or republication not permitted without written consent of the publisherDis Aquat Org 91: [257][258][259][260][261][262] 2010 ural rumen fluke infection in cattle and tapeworm infections in cats, dogs, sheep and chickens (Prasittirat et al. 1997).Both bithionol and bithionol sulphoxide have been examined as treatments for numerous fish parasites and showed mixed results. Santamarina et al. (1991) observed limited toxicity and complete in vitro efficacy against Gyrodactylus sp. in rainbow trout Oncorhynchus mykiss at 12.5 mg l -1 , with a minimum 20 mg l -1 reported as efficacious in vivo. Tojo et al. (1994b) stated that bithionol was efficacious in vivo against Ichthyobodo necator in rainbow trout at 25 mg l -1 for a 3 h freshwater bath on 2 consecutive days; however, higher concentrations exhibited some host toxicity. Moreover, Madsen et al. (2000) determined that bithionol at 0.1 mg l -1 was an effective treatment against trichodiniasis in European eels Anguilla anguilla, but found bithionol to have a relatively narrow therapeutic index. Bithionol was identified as being a potential candidate for the control of neoparmoebiasis with a demonstrated toxicity in vitro, although only 2 concentrations were tested . More recently, bithionol has displayed efficacy as a bath and oral treatment for Atlantic salmon experimentally challenged with Neoparamoeba spp., resulting in amoebic gill disease (AGD), at arbitary concentrations and dosages of 1 to 10 mg l -1 for bath treatments and 25 mg kg -1 feed (Florent et al. 2007a(Florent et al. ,...

In vitro gill cell monolayer successfully reproduces in vivo Atlantic salmon host responses to Neoparamoeba perurans infection

“…Currently, a commercial AGD vaccine is not available [17]. Though preliminary studies have been conducted to evaluate the efficacy of several potential chemotherapeutants [[18], [19], [20]], at present, exposure to freshwater remains the most effective treatment [21]. One of the key challenges to developing and evaluating new therapeutants is the availability of a cost effective ethically sound model system.…”

In vitro and in vivo efficacy of drugs against the protozoan parasite Azumiobodo hoyamushi that causes soft tunic syndrome in the edible ascidian Halocynthia roretzi (Drasche)

“…In the presence of this chemical, production of adenosine‐5′‐triphosphate is suppressed. Antiprotozoal effects have been reported against protozoans causing amoebic gill disease, Neoparamoeba in Atlantic salmon (Florent, Becker & Powell ), Ichthyobodo necator in rainbow trout (Tojo et al . ) and Trichodina in European eels (Madsen et al .…”

Electroanalysis of the Anthelmintic Drug Bithionol at Edge Plane Pyrolytic Graphite Electrode

“…Nowadays, bithionol is mainly used to treat sheep and cattle . This veterinary drug is known to affect electron transport, acting on the mitochondrial respiratory chain and suppressing ATP synthesis via uncoupling oxidative phosphorylation . Moreover, bithionol inhibits host caspases and reduces detrimental effects of anthrax lethal toxin, cholera toxin, diphtheria toxin, exotoxin A, Pseudomonas aeruginosa , Botulinum eurotoxin, ricin, and Zika virus .…”