Nuove acquisizioni sulle microsporidiosi ittiche / New knowledge on fish microsporidiosis.

SUMMARY - Microsporidians are obligate intracellular parasites that have been described from a range of vertebrate and invertebrate hosts. Although they have been considered protozoans for many years, recent phylogenetic and biosystematic analyses now place them within the kingdom Fungi. The aim of the present study was to expand and update current knowledge on fish microsporidiosis, with notable emphasis on their increasing importance in aquaculture and the zoonotic potential of certain fish microsporidians in immunocompromised human patients. During an examination of three farmed populations of sea bass Dicentrarchus labrax L. collected off the Tuscan and Apulian coast, a significant proportion of the fish (48.4%) were found to be infected with intestinal Microsporidia. Sea bass with a high intensity of infection were cachexic, with a poor average specific growth rate value when compared to their uninfected counterparts. As an earlier study on wild gobiids from the Gulf of Trieste also documented intestinal infections, the study was expanded to include an examination of Gobius niger L. (n = 5) and Gobius paganellus L. (n = 3) from the Adriatic Sea (Emilia-Romagna coast) such that infections in both the gobiids and the sea bass might be compared and to establish the potential role of gobiids as natural hosts of the parasitic infection. A histopathological study of the intestinal wall to assess the tropism of the parasites in conjunction with an assessment of spore and xenoma morphology suggested that the parasite bears similarities to species of the genus Glugea Thélohan, 1891 documented from sea bass. Only a single specimen of G. niger and one of the three G. paganellus that were sampled were positive for intestinal microsporidians. Although, the spores extracted from these hosts resemble those of Glugea, determination of their precise identity must await the results of an ongoing molecular study. While infections of the microsporidian isolated from sea bass appear to constitute a health risk to the industry further work is required to establish their host range and impact in each host they infect.