Comparative study of X-ray computerised tomography and conventional X-ray methods in diagnosis of swimbladder infection in eels caused by Anguillicola crassus

To date, swimbladder lesions due to Anguillicola crassus infection of the European eel Anguilla anguilla have so far been studied only by conventional X-ray methods. This is the first study to report the use of computerised tomography (CT) for studying lesions induced by anguillicolosis. Of 50 eels caught by electrofishery from Lake Balaton, Hungary, in autumn 2002 and pre-selected by a conventional X-ray method, 22 specimens were examined with a Siemens Somatom Plus S40 spiral CT scanner. Tomograms, radiographs and photographs of 5 of these, showing anguillicolosis-induced swimbladder lesions of varying severity, are presented. Computerised tomograms provide information on the inner structure, air content and wall thickness of the swimbladder as well as on the number of worms it contains. When the swimbladder is not severely affected or not completely filled with worms, computerised tomography provides adequate data on the shape of the swimbladder, thickness of the swimbladder wall and the location of worms in the lumen. However, in more severe cases, i.e. when the swimbladder is tightly packed with worms or contains no air as a result of wall-thickening, this method fails to determine the number and location of helminths or the thickness of the swimbladder wall.

Occurrence and pathology of Sinergasilus lieni (Copepoda: Ergasilidae), a parasite of the silver carp and bighead, in Hungarian ponds

Sinergasilus lieni Yin, 1949, a well-known and pathogenic parasitic copepod in China and Russia, has been detected in Hungarian carp farms for the first time. The parasite infected the third-year generation of silver carp (Hypophthalmichthys molitrix) and bighead (Aristichthys nobilis). The gills of the infected fish specimens showed severe pathological changes. At the attachment sites of female copepods clubbing and fusing of the gill filaments were observed and in some parts of the pale or whitish hemibranchia deep indentations were recorded in places where the tips of the damaged filaments had broken off. Silver carp and bighead were infected at a similar rate, having 8 to 27 copepods attached to the end of the clubbed filaments or the proliferated epithelium of 2 to 10 fused filaments. In histological sections the head part of the parasite was found in a deep cavity of the proliferated epithelium, piercing its antennae deep into the tissues. Only the end of the filaments showed changes. In this part the proliferated epithelium was infiltrated by eosinophilic granular cells. In the central and basal parts of the hemibranchia the original structure of the filaments was preserved with intact secondary lamellae.

Reno-, hepato- and splenomegaly of common carp fingerlings (Cyprinus carpio L.) diseased in swimbladder inflammation caused by Sphaerospora renicola Dyková et Lom, 1982

The weight of internal organs (swimbladder, kidney, liver, spleen) in relation to the body weight was studied in common carp fingerlings divided into three groups on the basis of swimbladder appearance and microscopic examination of the kidney. The fish had been collected from different Hungarian fish farms at the time when swimbladder inflammation (SBI) usually occurs (in July and August). The first group comprised fish with severe signs of SBI and massive renal sphaerosporosis, the second group consisted of fish with milder swimbladder changes and/or kidney infection by a low number of Sphaerospora renicola, while the third group was constituted by infection-free common carp fry. Statistical analysis of swimbladder, kidney, liver and spleen weight in relation to the body weight revealed that in the infected groups the internal organs were substantially enlarged. This suggests that in common carp fry with SBI the swimbladder changes are accompanied by reno-, hepato- and splenomegaly.

A survey of coccidian infections of freshwater fishes of Peninsular Malaysia, with descriptions of three species of Goussia Labbé, 1896 (Apicomplexa: Eimeriidae)

Ninety-five specimens of 14 freshwater fish species from small streams in the Kuala Terengganu district and the Lake Kenyir Reservoir, Malaysia, were surveyed for coccidian infections. Six fish species proved to be infected with apicomplexans belonging to the genus Goussia. In all of these fishes Goussia species were found in unsporulated and semisporulated stages. Oöcysts of four species inhabiting the intestinal epithelium became sporulated in tap-water within 24 hours. In two fish species sporulation failed and only unsporulated oöcysts were recorded in the intestine. Three of the intestinal species finishing sporulation proved to be new to science and were described as Goussia malayensis n. sp., G. bettae n. sp. and G. pogonognathi n. sp. from Apocheilus panchax, Betta splendens and Hemirhamphodon pogonognatus, respectively. The fourth species, found in Trichogaster pectoralis, was identified as G. trichogasteri Székely & Molnár, 1992, a species known from aquarium-cultured T. trichopterus.

A potential dual apical pathway in polarized regenerative cells of the midgut of Manduca sexta

Two novel proteins with apparent molecular weight of 38 (Manduca sexta midgut MsM38) and 46kDa (MsM46) were isolated from midgut homogenates in wandering stage Manduca sexta larvae and both of them were found to be present exclusively in this tissue on Western blots. Immunocytochemical studies revealed that both proteins are expressed in the regenerative cells however, their distribution pattern is clearly different. MsM38 is localized in the cytoplasm of resting regenerative cells during the feeding period, and is accumulated in the calcospherits at the beginning of the wandering period. Along with the delamination of the larval epithelium, this protein is released apically from these vesicles. The antiserum labels an additional 76 kDa protein in the wandering larval midgut homogenates. The appearance of this 76 kDa protein coincides with the accumulation of the immunopositive material in the calcospherits. MsM46 is similarly distributed during the feeding period in the cytoplasm of regenerative cells. At the beginning of the wandering period it accumulates around the newly forming large apical vacuoles, that are released at the time of complete delamination of the larval epithelium. In parallel with this process MsM46, and another 40 kDa protein, that becomes labeled from this period on Western blots appeares on the apical microvillar projections. Thus both isolated proteins are directed apically from different compartments, that raises the possibility of a dual apical routing pathway in regenerative cells.

The immunoprotein scolexin and its synthesizing sites--the midgut epithelium and the epidermis

Scolexin is one of the bacterial induced hemolymph proteins of tobacco homworm (Manduca sexta) larvae, that has hemocyte coagulation-provoking activity. The 72 kDa scolexin complex is composed of two 36 kDa subunits. To examine the protein secretory pathways in insect epithelia a polyclonal antibody was raised against the 36 kDa hemolymph protein. This MsH36 antibody recognised a 36 and a 72 kDa protein in tissue homogenates. On the basis of the characteristic labelling pattern observed on immunoblots and immunocytochemical sections we concluded that the 36 kDa protein in the hemolymph, in the midgut and in the epidermis was identical with the scolexin subunit. In present paper we report a labelling shift in the midgut epithelium between goblet and columnar cells that may be controlled by the hormonal system. A 72 kDa protein showed similar epitops and molecular weight to the scolexin complex and was detected in epidermis and in cuticle under both reducing and non-reducing conditions. Tissue localization of 36 kDa and 72 kDa MsH36 antibody labelling proteins indicated the possibility that the epidermal cells produce two kinds of scolexin-like proteins. The complex composed of 36 kDa subunits are transported basolaterally into the circulation and display hemocyte coagulation inducing activity while the 72 kDa form contains two subunits linked covalently secreted apically into the cuticle.

Development of Myxobolus macrocapsularis (Myxosporea: Myxobolidae) in an oligochaete alternate host, Tubifex tubifex

The development of Myxobolus macrocapsularis Reuss, 1906, a myxosporean parasite of the gills of common bream Abramis brama L., was studied in experimentally infected oligochaetes. In 3 experiments uninfected Tubifex tubifex Muller and Limnodrilus hoffmeisteri (Claparéde) were exposed to mature myxospores of M. macrocapsularis. In all experiments, typical triactinospores developed in T. tubifex specimens but no infection was found in L. hoffmeisteri. Triactinospores were released from oligochaetes 66 to 99 d after initial exposure. At that time pansporocysts containing 8 triactinospores were located in the gut epithelium of experimental oligochaetes, but free actinosporean stages were also found in the gut lumen of the oligochaetes. Each triactinospore had 3 pyriform polar capsules and a barrel-shaped sporoplasm with 32 secondary cells. The spore body joined the 3 caudal projections with a stout style.

Differences between the European carp (Cyprinus carpio carpio) and the coloured carp (Cyprinus carpio haematopterus) in susceptibility to Thelohanellus nikolskii (Myxosporea) infection

Thelohanellus nikolskii infection of the common carp (Cyprinus carpio L.) has been a common parasitosis in the Central European fish farms since the first detection of the parasite about 20 years ago. This parasite, introduced from the Far East, causes intensive infection on the fins of fingerlings of the carp subspecies cultured in Europe (European carp, Cyprinus carpio carpio). This infection of the common carp occurs in the Hungarian fish farms every year. Until the present study, this parasite had not been recorded from the fins of koi or coloured carp (Cyprinus carpio haematopterus), a carp of Far Eastern origin, which is cultured in Hungary as an ornamental fish. A recent survey conducted in common carp, koi and goldfish stocks demonstrated that T. nikolskii infection of low prevalence and intensity occurs also in koi populations, but its prevalence and intensity are markedly lower than in common carp kept in the same ponds. It is suggested that the observed differences are due to disparities in the susceptibility of the two carp subspecies to T. nikolskii, and that the koi is less susceptible to this infection. Other signs of susceptibility can also be observed in the European subspecies, since in 15% of the fish plasmodium development was arrested at an early stage. Thelohanellus nikolskii infection could not be demonstrated on goldfish (Carassius auratus).

Comparative ultrastructure of the actinosporean stages of Myxobolus bramae and M. pseudodispar (Myxozoa)

The ultrastructrure of triactinospores and other developmental stages obtained after the experimental infection of the oligochaete Tubifex tubifex with myxospores of Myxobolus bramae and Myxobolus pseudodispar was studied. In both cases, pansporocysts harbouring spores and the remnants of polar bodies were found in the gut epithelium of the tubificids. Other stages were also seen in M. pseudodispar. Capsulogenic cells surrounded the apical part of the sporoplasm in M. bramae whereas they were located separately in M. pseudodispar. The sporoplasm of M. bramae was elongated and was filled with numerous infective cells, whereas secondary cells rarely appeared in the sporoplasm of M. pseudodispar, which contained large groups of beta-glycogen granules. Other M. pseudodispar stages included pansporocysts harbouring pregametic or gametic stages, zygotes, or the initial steps of sporogenesis. The presence of first- and second-order polar bodies indicates the existence of meiosis. In the spores of M. pseudodispar, the presence of desmosome-like junctions between the capsulogenic cells, and hemidesmosome-like junctions between the capsulogenic cells and the inner membrane of the valvogenic cells, is remarkable.

Antineutrophil cytoplasmic antibodies in patients with systemic lupus erythematosus

We determined the prevalence of antineutrophil cytoplasmic antibodies (ANCAs) in patients with systemic lupus erythematosus (SLE) and evaluated the correlation between ANCA positivity and clinical features. Forty-one patients with SLE and two control groups were examined. One of the control groups consisted of 15 patients with systemic vasculitis, and the other of 12 healthy blood donors. A quantitative enzyme-linked immunosorbent assay technique was used to measure the serum cytoplasmic ANCA (cANCA) and perinuclear ANCA (pANCA) levels. cANCA positivity was found in three patient samples, and pANCA positivity in 10 SLE patients. The occurrence and titres of both ANCA types in SLE patients were similar to those in healthy controls and significantly lower than those in patients with systemic vasculitis. The clinical picture and antibody profile were similar in ANCA-positive and ANCA-negative SLE patients. We conclude that measurement of ANCAs does not provide any additional diagnostic or prognostic data in SLE.

Radiodiagnostic examination of the swimbladder of some fish species

Radiodiagnostic methods have not been used previously for studying the anatomy and diseases of the swimbladder of freshwater fish species. In this study, the radiographic anatomy of the swimbladder and species-related differences in swimbladder structure were studied on plain radiographs taken of 12 Hungarian fish species of major economic importance. Changes observed by radiography were also studied by conventional parasitological methods. The radiodiagnostic method reported here appears to be a useful complement to diagnostic examinations that have been based merely on dissection so far. It enables evaluation of the pathological lesions in live condition, without causing damage to the fish.

Distribution of serpins in the tissues of the tobacco hornworm (Manduca sexta) larvae. Existence of new serpins possibly encoded by a gene distinct from the serpin-1 gene

Polyclonal antibodies were raised against the isolated hemolymph serine proteinase inhibitors (serpins) of Manduca sexta larvae. Two of these antibodies, MsH49a and MsH49b, displayed characteristic differences in labelling patterns of hemocytes, fat body, integumental epidermis and cuticle on immunoblots, and in light- and electronmicroscopic sections. The serpin composition of the latter three tissue homogenates was determined by native immunoblots and inhibitor binding assays. The results were compared to the hemolymph samples containing all the known inhibitors encoded by the well-characterized serpin-1 gene. The enzyme specificity of the MsH49b-labelled cuticular serpin was similar to serpin-1J, although its electrophoretic mobility on native PAGE was not identical with any of the known proteinase inhibitors encoded by the serpin-1 gene. Based on these data, we suggest that the cuticle and hemolymph may contain novel serpin(s) encoded by a gene other than the serpin-1 gene. Since the serpin-1J proved to be involved in the activation pathway of the prophenoloxidase system in the hemolymph, the in vivo function of cuticular MsH49b serpin was investigated by prophenoloxidase tests in native cuticular homogenates. Our results demonstrated that the cuticular serpin(s) that are labelled by the MsH49b antibody may play a determinant role in the regulation of the prophenoloxidase system of the integumental cuticle.

Survey on Myxobolus infection of the bleak (Alburnus alburnus L.) in the river Danube and in Lake Balaton

In a three-year survey of myxosporean infections of the bleak (Alburnus alburnus), involving the examination of 205 fish specimens from the River Danube and 50 from Lake Balaton, four Myxobolus species (two gill parasites, one fin parasite and a species parasitising the skeletal muscles) were detected. Two of the species could be identified as M. alburni and M. obesus. Of the other two species, the gill parasite proved to be a hitherto undescribed species which is described here as a new species by the name of M. margitae. One of the two gill-parasitic species, M. obesus, formed plasmodia in the respiratory lamellae of the gill filaments, while the plasmodia of M. margitae n. sp. were formed in the afferent artery of the primary gill filaments. The plasmodia containing spores morphologically identifiable with the species M. alburni were located in the connective tissue between the fin rays. The less frequently found muscle-parasitic Myxobolus species has not been identified precisely. The plasmodia of M. obesus were found in the fish in May and June, while those of M. alburni and M. margitae n. sp. in July and August. The prevalence of infection in fish examined in these periods was 15.5% for M. obesus, 11.5% for M. margitae and 14.0% for M. alburni.

Myxobolus intrachondrealis sp. n. (Myxosporea: Myxobolidae), a parasite of the gill cartilage of the common carp, Cyprinus carpio

A species not identifiable with any of the about 23 Myxobolus species recorded from the common carp so far, was detected in the gills of one- and two-summer-old specimens of the common carp ((Cyprinus carpio L.) cultured in pond farms in Hungary. The strictly tissue-specific plasmodia of the parasite were located, surrounded by hyaline cartilage cells, in the chondrous substance of the terminal parts of the gill arches and in the cartilage structure ventrally connecting the gill arches. The spores of the parasite described as Myxobolus intrachondrealis sp. n. developed in globular or ellipsoidal plasmodia measuring 300-600 microm. By their elongated ellipsoidal shape and similarly elongated polar capsules the spores were well distinguishable from the hitherto described Myxobolus species parasitic in the common carp and also from the cartilage-parasitic Myxobolus species of other fishes.

Identification of fish-parasitic Myxobolus (Myxosporea) species using a combined PCR-RFLP method

Polymerase chain reaction (PCR) with primers specific for the family Myxobolidae was used to amplify a part of the 18S ribosomal RNA gene of Myxobolus species. The length of the amplified fragments was approximately 1600 base pairs. Six Myxobolus species identified on the basis of morphological features were compared using a combined PCR-RFLP method. The cleavage patterns generated by 2 frequent cutter restriction enzymes (HinfI and MspI) were suitable for the differentiation of the examined Myxobolus species.

A survey on coccidian infection of Lake Biwa fishes in Japan, with the description of four new species of Goussia labbe, 1896 (Apicomplexa)

Thirty-two specimens of 11 freshwater fish species from Lake Biwa, Japan were surveyed for coccidian infections. Four fish species proved to be infected with apicomplexans belonging to the genus Goussia. Altogether, seven Goussia species were found. Oöcysts of four species inhabiting the intestinal epithelium were shed at the sporulated stage. Two other intestinal species left the fish unsporulated. A few relatively large and aged oöcysts of a further species were found in the renal tubules. The sporulated intestinal species were described as Goussia biwaensis n. sp., G. grygieri n. sp., G. nipponica n. sp. and G. wakabayashii n. sp.

Development of a system for detection of circulating antibodies against hemidesmosomal proteins in patients with bullous pemphigoid

Specific antibodies directed against special hemidesmosomal proteins are involved in the pathogenesis of bullous pemphigoid (BP), and detection of these antibodies is crucial for a correct diagnosis. As the BP autoantigen primary structures are known, the question was addressed as to whether it is possible to demonstrate circulating antibodies against BP autoantigens (BPAG1 and BPAG2) by means of an ELISA system, using antigenic epitopes. With the help of the programs Peptidestructure and Plotstructure, antigenic epitopes of BP antigens were predicted, chemically synthesized and screened using serum from 43 proven BP patients. The coding sequences of the best antigenic epitopes were then chemically synthesized and inserted as monomer and homo- or hetero-oligomer forms into fusion-expression plasmids (PGEX-4T, Pharmacia) in-frame to the C-terminus of glutathione-S-transferase. Fusion products were expressed and purified from Escherichia coli cells by affinity chromatography. The recombinant proteins were used for the detection of antibodies in the serum of 43 BP patients and of 60 controls (including 30 healthy persons, 22 patients with pemphigus vulgaris and 8 patients with other bullous dermatoses). Use of the homo- and hetero-oligomers of the recombinant fusion peptides increased the sensitivity of the disease-specific antibody detection. When a mixture of the best recombinant fusion proteins was used, the sensitivity of the ELISA assays in the case of the BP patients' serum was 0.90. This system could form the basis of a rapid and simple system for the diagnosis of BP.

Myxobolus infection of the gills of common bream (Abramis brama L.) in Lake Balaton and in the Kis-Balaton reservoir, Hungary

During a five-year survey including studies on the parasite fauna of bream (Abramis brama), four gill-parasitic Myxobolus species (M. bramae, M. hungaricus, M. impressus and M. macrocapsularis) were recorded in a total of 313 breams from Lake Balaton. The commonest species, M. bramae showed a prevalence of 33%, while the other species occurred sporadically. Myxobolus bramae and M. macrocapsularis infected the tips of the gill filaments and caused both intralamellar and interlamellar infection. Intralamellar plasmodia of small size developed in the capillary network of the gill lamellae whereas the much larger interlamellar plasmodia were formed in the arteria afferens. The intralamellar plasmodia of M. hungaricus always infected the basal or central part of the gill filaments. In contrast to the above species developing in the blood vessels, M. impressus proved to be an epithelial parasite, as its plasmodia always developed in the adjacent gill filaments of two opposite haemibranchia, in the stratified epithelium between the respiratory plates, causing changes of the haemibranchium which were well visible even by the naked eye.

Experimental detection of the actinospores of Myxobolus pseudodispar (Myxosporea: Myxobolidae) in oligochaete alternate hosts

The development of Myxobolus pseudodispar Gorbunova, 1936, an intracellular myxosporean muscle parasite of the roach Rutilus rutilus L., was studied in experimentally infected oligochaetes. In one experiment, uninfected Tubifex tubifex Müller and Limnodrilus hoffmeisteri (Claparéde) were exposed to mature spores of M. pseudodispar. Triactinomyxon spores developed both in T. tubifex and L. hoffmeisteri specimens. Triactinospores were first released from the oligochaetes 76 d after initial exposure. At that time, pansporocysts containing 8 triactinospores were located in the gut epithelium of experimentally infected oligochaetes, but free actinosporean stages were also found in their gut lumen. Each triactinospore had 3 pyriform polar capsules and an elongated cylindrical sporoplasm with 8 secondary cells. The spore body joined the 3 caudal projections with a relatively long style. One of the 3 caudal projections was shorter than the other two. The total length of the triactinospore was on average 206.5 microns.

Redescription of Myxobolus hungaricus Jaczó, 1940 (Myxosporea: Myxobolidae), a parasite of bream (Abramis brama L.)

Myxobolus hungaricus Jaczó, 1940 forms relatively large plasmodia on the gills of bream (Abramis brama). The authors give a redescription of this deficiently described parasite on the basis of spores collected from the original habitat, which spores are indicated as a neotype. The plasmodia of the parasite can be found on the gills typically in the spring months, and are located in the central part of the gill filaments. They start to develop in the lumen of capillaries of the secondary lamellae and remain in intralamellar location also after they have reached the mature stage. The spores have a very characteristic shape, as on the surface of the spore valves a distinctly emerging ridge runs parallel to the sutural line. In addition to breams from the typical habitat, Lake Balaton, the plasmodia of M. hungaricus could be detected also on breams originating from the river Danube.

Isolation and characterization of an apically sorted 41-kDa protein from the midgut of tobacco hornworm (Manduca sexta)

Immunocytochemical localization and sorting properties of a newly purified 41-kDa protein (MsM41) were investigated in an insect, the tobacco hornworm Manduca sexta. The protein purified from midgut homogenates of feeding fifth-stadium larvae was found exclusively in this tissue on Western blots. Presence of MsM41 protein was indicated in both anterior and posterior regions of the midgut during the whole fifth stadium. However, in the posterior region an additional 39-kDa protein was also detected during the feeding period of the last larval stage. Upon light-microscopic examination immunoreactivity was localized in the columnar cells, while the goblet, endocrine and regenerative cells remained unlabeled. Distribution of the label during the feeding period was different in the anterior and posterior regions. In the anterior region immunoreactivity was localized only to the brush border membrane of columnar cells, while in the posterior region some cytoplasmic structures identified as large trans-Golgi vesicles, endoplasmic reticulum and small secretory vesicles were also labeled. Large, apical extrusions remained immunonegative. In vitro translation confirmed that our protein was expressed only in the posterior region of the midgut. The primary translation product was a 39-kDa protein. Putative post-translational modifications yielded the 41-kDa form, which was then secreted apically. Its presence in the region of the anterior part microvilli was probably due to the countercurrent flux of the ectoperitrophic fluid.

Insect cuticle, an in vivo model of protein trafficking

In the course of this study more than 20 proteins have been isolated from the larval cuticle of Manduca sexta. Synthesis, secretion, transport and accumulation of four particular proteins, representative members of four characteristic groups, were followed during metamorphosis by immunoblot and immuncytochemical methods and are described in detail in this paper. We established that only some of the proteins of the soft cuticle of Lepidopteran larvae are synthesized in epidermal cells at the beginning of the larval stages and are digested during the moulting period (MsCP29). Other proteins (MsCP30/11) are secreted into the cuticle by the epidermal cells in different forms during various developmental stages. Some proteins are secreted apically during the feeding period, but before ecdysis they are then taken up by epidermal cells and transported in a basolateral direction back into the hemolymph and saved in an immunologically intact form by the fat body cells (MsCP12.3). Some cuticle proteins have a non-epidermal origin. They are transported from the hemolymph into the cuticle. Before and during ecdysis these molecules reappear in the hemolymph and are detectable again in the pupal cuticle (MsCP78). Our data prove that the cuticle is not a non-living part of the insect body: it is not only an inert, protective armor, but maintains a continuous and dynamic metabolic connection with the other organs of the organism.

Antineutrophil cytoplasmic antibodies and other immunologic abnormalities in patients with habitual abortion

PROBLEM

The immunologic mechanisms of pregnancy loss in habitual aborters with antiphospholipid and antinuclear antibodies have not been fully clarified. The possible association of antineutrophil cytoplasmic antibodies (ANCAs) with recurrent miscarriage was examined.

METHOD OF STUDY

In a prospective, controlled trial of 59 women with recurrent abortion, the prevalence of pANCA (antimyeloperoxidase), cANCA (antiproteinase-3), and immunoserologic abnormalities of systemic lupus erythematosus (SLE) anti double-stranded DNA, anti-SSA, anti-SSB, anti-U1RNP, anti-Sm, anticardiolipin and antinuclear antibodies, LE-cell, lupus anticoagulant, and complement-3 were investigated.

RESULTS

pANCA occurred in 2, and cANCA in 6 of 59 case patients, but neither was observed in the controls (P = 0.09 for cANCA). cANCA levels were significantly higher in patients than in controls (P = 0.028). Six recurrent aborters were identified as having a group of immunoserologic abnormalities characteristic of SLE.

CONCLUSIONS

Immunologic mechanisms detectable in SLE may operate in a subgroup of habitual aborters with suspected immunologic cause. ANCAs occur more frequently in patients with recurrent miscarriage than in controls.

Relationships among members of the genus Myxobolus (Myxozoa: Bilvalvidae) based on small subunit ribosomal DNA sequences

Sequences representing approximately 1,700 base pairs of the 18S rRNA gene from 10 different species in the genus Myxobolus were found to group them into 3 clusters that showed little correlation with spore morphology and size or host specificity, criteria currently used for both higher and lower taxonomic placements in the Myxozoa. Of the phenotypic criteria examined, tissue tropism was most correlated with the rRNA groupings observed. Spores of similar size and shape (Myxobolus cerebralis vs. Myxobolus squamalis) were distantly related in some instances, whereas spores with divergent morphology and size were sometimes found to be closely related (M. cerebralis and Myxobolus insidiosus). These initial investigations into the phylogenetic relationships of putative members of the genus Myxobolus clearly indicate the potential limitations of groupings based on size and morphological properties of the spores and host species infected. We propose that 18S rRNA gene sequences, combined with information on tissue tropism, host species infected, and developmental cycles in the fish and alternate host (when and if known) be given greater consideration in taxonomic placements of myxosporeans.