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Red Mark Syndrome (RMS) is a skin condition affecting farm-reared rainbow trout Oncorhynchus mykiss. Although RMS is non-debilitating for fish, it causes serious economic losses to fish farm. Previous studies suggested a bacterium from the family "Candidatus Midichloriaceae ", indicated as Midichloria-1ike organism (MLO), as a possible etiological agent for RMS, but this hypothesis has not been confirmed yet.
In the ciliate fish parasite Jchthyophthirius multifiliis, some bacteria highly similar to RMS-MLO were found as endosymbionts, thus it can be hypothesized that I. multifiliis, or other ciliates, may act as vector or facilitate the transmission of RMS.
The main purpose of this study was to verify if bacteria from "Candidatus Midichloriaceae" can infect 1 multifiliis when exposed to RMS diseased fish. Specific Pathogen Free (SPF) fish were employed for I. multifiliis production, adding two SPF fish in two tanks. Once these trouts were ready to shed I. multifzliis, SPF rainbow trout was euthanized and transferred to a small aquarium. During maturation of I multifiliis, fish started to present the typical white spots caused by parasitic ciliate infection, and at this stage, I multifiliis jumped out from the fish epithelia (TO). A part of these ciliates was kept in the aquarium until theronts were released, then a suitable amount was added together with water in tanks containing large SPF and RMS fish. The rest of 1 multifzliis was fixed for different analysis aimed to verify if these ciliates hosted the MLO.
The previous steps, necessary to prepare 1 multifiliis infection, were repeated and two separate infection experiments were carried out (Tl =first infection experiment; and T2=second infection experiment). 1 multifiliis cells were checked by fluorescence in situ hybridization, and the presence of MLO was detected in 1 multifiliis both in Tl and T2.
Different combination of specific MLO primers were used to characterize the MLO organisms observed in 1 multifzliis infected cells from Tl and T2. The sequence obtained was 1008 bp long and 99.14%identical with Rickettsia-like organism from rainbow trout (EU555284, Lloyd et al. 2008) and 99.12%identical with bacterium associated to 1 multifiliis (KT85 l 863, Zaila et al. 2017).
In conclusion, RMS-MLO can infect 1 multifiliis when this ciliate is exposed to RMS diseased fish, thus opening new interesting perspectives aimed to study the development of RMS thanks to the future genomic analysis.
Period25 Sep 201828 Sep 2018
Event title79 Congresso Nazionale Unione Zoologica Italiana
Event typeConference
LocationLecce, Italy
Degree of RecognitionNational