A histochemical study using lectin methods was performed on myxosporean parasites from vastly different fish hosts from marine and fresh waters. Six biotinylated lectins were used (WGA, SBA, BS-I, Con-А, UEA-I and SNA). The binding paltem of Con-A and WGA revealed the presence of mannose and/or glucose, and N-acetyl-D-glucosamine respectively, in polar capsules and valves of most of the myxosporea assayed. Thus, chitin may be present in polar capsules and/or valves of myxosporean spores. The BS-I binding pattern showed the presence of a-!)-galactose and/or N-acetyl-D-galactosamine residues in polar capsules of Kudoa sp., Zschokkeìla mugilis Sitjà-Bobadilla et Alvarez-Pellitero, 1993 and Leplotheca sp., and in the valves of the latter. Scarce amounts of N-acetyl-D-galactosamine and/or α-D-galactose were demonstrated by SBA binding in Sphaerospora dicentrarchi Sitjà-Bobadilla et Alvarez-Pellitero 1992, Leplotheca sp. and Kudoa sp. valves, and in Leptotheca sp. polar capsules. The UEA-I staining indicated the absence ofa-L-fucose in all the myxosporea assayed except in Leptotheca sp. N-acety!neuraminic acid was detected with SNA in the polar capsules and sporoplasms of Polysporoptasma sparis Sitjà-Bobadilla et-Alvarez-Pellitero, 1995 and in the polar capsules and valves of Kudoa sp. These results indicate that, although Myxosporea may have conserved carbohydrate structures, some of them can show significantly different binding patterns, which may be useful in diagnostic and functional studies.
The polyopisthocotylean Sparicotyle chrysophrii (Van Beneden et Hesse, 1863) was experimentally transmitted to gilthead seabream (Sparus aurata L.) by exposure to eggs (EGT) and by cohabitation with naturally parasitized fish (CT). In EGT trials, the infection was successfully transmitted by introducing containers with monogenean eggs in the fish tanks, with the highest infection level (85.7% prevalence, 3.3 mean intensity) achieved at 6 weeks post exposure (p.e.) to the infection dose of 650 eggs per tank. In CT trials, the progression of the infection was faster and reached higher levels than in EGT. When using small fish juveniles (30 g) (CT-2), infection reached 100% prevalence (mean intensity 8 monogeneans/fish) at 5 weeks p.e., but no eggs could be found in the fish even 10 weeks p.e. By contrast, when larger juveniles (150 g) were used (CT-1), infection levels were lower, but mature adults with eggs were detected starting from 8 weeks p.e. The effect of the parasite on the condition factor, haematocrit, haemoglobin concentration (Hb), red blood cell counts, mean corpuscular haemoglobin concentration (MCHC), mean corpuscular haemoglobin content (MCH) and mean cellular volume (MCV) of infected fish was studied in CT trials. The infection produced hypochromic anaemia, since Hb concentration significantly decreased at 5 and 10 weeks p.e. in CT-2 and at 8 weeks p.e. in CT-1. MCHC was significantly lower in parasitized than in control fish at 5 and 8 weeks p.e. in CT-2 and CT-1, respectively. Also in CT-1, MCH was lower and circulating immature erythrocytes, granulocytes and plasma cells were higher in infected fish than in control ones at 8 weeks p.e. The histopathological effects of the monogenean on the gills of naturally infected fish consisted of lamellar shortening, clubbing and synechiae. The proliferation of the epithelial tissue produced fusion of secondary lamellae, and abundant chloride cells were observed.
Systemic ciliatosis caused by histophagous ciliates constitutes a serious disease of cultured turbot. Six ciliate isolates were obtained from parasitized turbot during six epizootics at four different farms located in Spain, France and Portugal. Axenic cultures of the six isolates were obtained by periodical subculturing in ATCC 1651MA or supplemented L-15 media. In basal media or seawater, the parasites could survive starving for long periods with no apparent proliferation. In adequate media, growth kinetics was found to be very similar for isolates A and B, with a clear influence of temperature. Morphological studies demonstrated that all isolates share common features that allows their assignment to either Philasterides Kahl, 1931 or Miamiensis Thompson et Moewus, 1964. However, statistically significant differences were evident in pairwise comparisons of the isolates from the four farm sites in 16 taxonomically relevant morphometric features. This could allow the discrimination of different species or strains. Virulence of isolates A and B for healthy turbot was tested in several experiments. Differences in the virulence were especially evident after long-term in vitro culturing, isolate A being clearly attenuated after 35-42 passages, whereas isolate B became more virulent after 20-42 passages. The need of further studies to confirm such virulence variability and its implications in pathogenesis and prevention of turbot scuticociliatoses is stressed.
The presence of terminal carbohydrate residues in Enteromyxum leei (Diamant, Lom et Dyková, 1994) Palenzuela, Redondo et Álvarez-Pellitero, 2002 stages in gilthead seabream intestines was studied at light microscopy (LM) and transmission electron microscopy (TEM) level using lectin histochemical techniques. Abundant mannose and/or glucose residues were demonstrated by the intense staining caused by binding of biotinylated concanavalin A (Con A), at both LM and TEM. A clear positivity was also obtained with Ulex europaeus (UEA I) agglutinin specific for fucose residues. Both lectins stained E. leei proliferative and sporogonic stages, though glycan patterns varied between these developmental stages. Wheat germ agglutinin (WGA) and Bandeiraea simplicifolia lectin I (BSL I) recognised only structures in the sporogonic stages. Faint labelling occurred with Glycine max (SBA) lectin. No staining was obtained with Sambucus nigra (SNA) agglutinin. The TEM studies demonstrated a restricted presence of N‑acetyl-D-galactosamine and α-D-galactose, whereas glucose/mannose and fucose, the dominant structures, were also present at the parasite membranes and host-parasite interface, suggesting a role in host-parasite interaction.
In order to elucidate the transmission and dispersion routes used by the myxozoan parasite Enteromyxum scophthalmi Palenzuela, Redondo et Alvarez-Pellitero, 2002 within its host (Scophthalmus maximus L.), a detailed study of the course of natural and experimental infections was carried out. Purified stages obtained from infected fish were also used in in vitro assays with explants of uninfected intestinal epithelium. The parasites can contact and penetrate loci in the intestinal epithelium very quickly. From there, they proliferate and spread to the rest of the digestive system, generally in an antero-posterior pattern. The dispersion routes include both the detachment of epithelium containing proliferative stages to the intestinal lumen and the breaching of the subepithelial connective system and local capillary networks. The former mechanism is also responsible for the release of viable proliferative stages to the water, where they can reach new fish hosts. The finding of parasite stages in blood smears, haematopoietic organs, muscular tissue, heart and, less frequently, skin and gills, suggests the existence of additional infection routes in transmission, especially in spontaneous infections, and indicates the role of vascular system in parasite dispersion within the fish. The very high virulence of this species in turbot and the rare development of mature spores in this fish may suggest it is an accidental host for this parasite. This may also question the existence of a two-host life cycle involving an actinosporean stage in this species. Further studies are needed to clarify this open point of the life cycle.