In Vitro Testing of Alternative Synthetic and Natural Antiparasitic Compounds against the Monogenean Sparicotyle chrysophrii.

Adrián Ormad-García,Cristobal Espinosa Ruiz,Oswaldo Palenzuela,Željka Trumbić,Ariadna Sitjà-Bobadilla,Simona Manuguerra,Concetta Maria Messina,Ivona Mladineo

doi:10.3390/pathogens10080980

Abstract

Gill monogenean Sparicotyle chrysophrii is considered the most detrimental fish parasite to the Mediterranean aquaculture. Treatment of sparicotylosis relies on frequent gill inspections correlated with the seasonal increase in seawater temperature, application of functional feeds, and treatments with formalin baths where permitted. While the latter is bound to be banned in Europe, other synthetic anthelminthics, such as praziquantel and ivermectin, are prone to induce resistance in the parasites. Therefore, we investigated, in vitro, 14 synthetic and natural compounds against adult S. chrysophrii, developing dose–response modelsm and estimated toxicity levels at 20%, 50%, and 80% parasite mortality. Bactericidal activity of target compounds was also tested in two important aquaculture bacteria; Vibrio harveyi and V. anguillarum, while their potential host toxicity was evaluated in gilthead seabream SAF-1 cell line. Synthetic compound bithionate sodium exerted the most potent toxicity against the monogenean, no host cytotoxicity, and a medium and high potency against two bacterial pathogens. In comparison, target natural compounds were approximately 20 (cedrol) or up to 154 times (camphor) less toxic for the monogenean. Rather than completely dismissing natural compounds, we suggest that their application in combination with synthetic drugs, especially if administered in the feed, might be useful in sparicotylosis treatment.

Highlights

Sparicotylosis is a detrimental parasitic disease affecting gilthead sea bream Sparus aurata that results in significant losses in Mediterranean-wide aquaculture
Apart of being banned in Italy, which likely is soon to be followed by the rest of EU, formalin application in sea cages has shown many drawbacks; a narrow therapeutic range, irritation of the gill epithelium, induction of hypoxia when applied in warm periods, toxicity to invertebrates in the water column, and sediment, toxicity, and carcinogenicity for the handling employees, as well as large operational costs [7,8], the latter, being common for any other compound applied in sea cages
Bithionol was encompassed in an array of topical drugs against liver trematodes in humans [13], but it has been dismissed given its potent photosensitizing activity that results in serious skin disorders

Summary

Introduction

Sparicotylosis is a detrimental parasitic disease affecting gilthead sea bream Sparus aurata that results in significant losses in Mediterranean-wide aquaculture. In a commercial outgrowth cycle of gilthead sea bream in sea cages, for producing 100,000 fish, 12 tons of formalin are used for controlling this disease. Apart of being banned in Italy, which likely is soon to be followed by the rest of EU, formalin application in sea cages has shown many drawbacks; a narrow therapeutic range, irritation of the gill epithelium, induction of hypoxia when applied in warm periods, toxicity to invertebrates in the water column, and sediment, toxicity, and carcinogenicity for the handling employees, as well as large operational costs [7,8], the latter, being common for any other compound applied in sea cages

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