Fluorescent tagging of Plasmodium circumsporozoite protein allows imaging of sporozoite formation but blocks egress from oocysts

The circumsporozoite protein, CSP, is the major surface protein of Plasmodium sporozoites, the form of malaria parasites transmitted by mosquitoes. CSP is involved in sporozoite formation within and egress from oocysts, entry into mosquito salivary glands and mammalian liver as well as migration in the skin. Yet, how CSP facilitates sporozoite formation, oocyst egress and hepatocyte specific invasion is still not fully understood. Here, we aimed at generating a series of parasites expressing full-length versions of CSP with internally inserted green fluorescent protein between known domains at the endogenous csp locus. This enabled the investigation of sporozoite formation in living oocysts. GFP insertion after the signal peptide leads to cleavage of GFP before the fusion protein reached the plasma membrane while insertion of GFP before or after the TSR domain prevented sporozoite egress and liver invasion. These data suggest different strategies for obtaining mature salivary gland sporozoites that express GFP-CSP fusions.

Deciphering host lysosome-mediated elimination of Plasmodium berghei liver stage parasites

Liver stage Plasmodium parasites reside in a parasitophorous vacuole (PV) that associates with lysosomes. It has previously been shown that these organelles can have beneficial as well as harmful effects on the parasite. Yet it is not clear how the association of lysosomes with the parasite is controlled and how interactions with these organelles lead to the antagonistic outcomes. In this study we used advanced imaging techniques to characterize lysosomal interactions with the PV. In host cells harboring successfully developing parasites we observed that these interaction events reach an equilibrium at the PV membrane (PVM). In a population of arrested parasites, this equilibrium appeared to shift towards a strongly increased lysosomal fusion with the PVM witnessed by strong PVM labeling with the lysosomal marker protein LAMP1. This was followed by acidification of the PV and elimination of the parasite. To systematically investigate elimination of arrested parasites, we generated transgenic parasites that express the photosensitizer KillerRed, which leads to parasite killing after activation. Our work provides insights in cellular details of intracellular killing and lysosomal elimination of Plasmodium parasites independent of cells of the immune system.

Detection of Plasmodium berghei infected Anopheles stephensi using near-infrared spectroscopy

BACKGROUND

The proportion of mosquitoes infected with malaria is an important entomological metric used to assess the intensity of transmission and the impact of vector control interventions. Currently, the prevalence of mosquitoes with salivary gland sporozoites is estimated by dissecting mosquitoes under a microscope or using molecular methods. These techniques are laborious, subjective, and require either expensive equipment or training. This study evaluates the potential of near-infrared spectroscopy (NIRS) to identify laboratory reared mosquitoes infected with rodent malaria.

METHODS

Anopheles stephensi mosquitoes were reared in the laboratory and fed on Plasmodium berghei infected blood. After 12 and 21 days post-feeding mosquitoes were killed, scanned and analysed using NIRS and immediately dissected by microscopy to determine the number of oocysts on the midgut wall or sporozoites in the salivary glands. A predictive classification model was used to determine parasite prevalence and intensity status from spectra.

RESULTS

The predictive model correctly classifies infectious and uninfectious mosquitoes with an overall accuracy of 72%. The false negative and false positive rates were 30 and 26%, respectively. While NIRS was able to differentiate between uninfectious and highly infectious mosquitoes, differentiating between mid-range infectious groups was less accurate. Multiple scans of the same specimen, with repositioning the mosquito between scans, is shown to improve accuracy. On a smaller dataset NIRS was unable to predict whether mosquitoes harboured oocysts.

CONCLUSIONS

To our knowledge, we provide the first evidence that NIRS can differentiate between infectious and uninfectious mosquitoes. Currently, distinguishing between different intensities of infection is challenging. The classification model provides a flexible framework and allows for different error rates to be optimised, enabling the sensitivity and specificity of the technique to be varied according to requirements.

Reclassification of Eimeria pogonae Walden (2009) as Choleoeimeria pogonae comb. nov. (Apicomplexa: Eimeriidae)

The presented paper provides a reclassification of Eimeria pogonae from Pogona vitticeps into the correct genus Choleoeimeria. A description of exogenous and endogenous stages of biliary coccidium is given. Sporulation of the oocysts was endogenous. The mature oocysts contained four sporocysts each with two sporozoites. Oocysts were ellipsoidal in shape, with average length/width ratio 1.7 and measured 28.4 (SD1.5) × 16.8 (SD 1.5). The micropyle, residuum, and polar granules were absent from the sporulated oocysts. Ovoidal in shape, sporosysts without Steida bodies contained residuum and two elongated and boat-shaped sporozoites. The endogenous stages of the coccidia were located mainly in the epithelium of bile ducts; however, single-epithelium cells of the gallbladder were also infected.

The repeat region of the circumsporozoite protein is critical for sporozoite formation and maturation in Plasmodium

The circumsporozoite protein (CSP) is the major surface protein of the sporozoite stage of malaria parasites and has multiple functions as the parasite develops and then migrates from the mosquito midgut to the mammalian liver. The overall structure of CSP is conserved among Plasmodium species, consisting of a species-specific central tandem repeat region flanked by two conserved domains: the NH₂-terminus and the thrombospondin repeat (TSR) at the COOH-terminus. Although the central repeat region is an immunodominant B-cell epitope and the basis of the only candidate malaria vaccine in Phase III clinical trials, little is known about its functional role(s). We used the rodent malaria model Plasmodium berghei to investigate the role of the CSP tandem repeat region during sporozoite development. Here we describe two mutant parasite lines, one lacking the tandem repeat region (ΔRep) and the other lacking the NH₂-terminus as well as the repeat region (ΔNΔRep). We show that in both mutant lines oocyst formation is unaffected but sporozoite development is defective.

Transition of Plasmodium sporozoites into liver stage-like forms is regulated by the RNA binding protein Pumilio

Many eukaryotic developmental and cell fate decisions that are effected post-transcriptionally involve RNA binding proteins as regulators of translation of key mRNAs. In malaria parasites (Plasmodium spp.), the development of round, non-motile and replicating exo-erythrocytic liver stage forms from slender, motile and cell-cycle arrested sporozoites is believed to depend on environmental changes experienced during the transmission of the parasite from the mosquito vector to the vertebrate host. Here we identify a Plasmodium member of the RNA binding protein family PUF as a key regulator of this transformation. In the absence of Pumilio-2 (Puf2) sporozoites initiate EEF development inside mosquito salivary glands independently of the normal transmission-associated environmental cues. Puf2- sporozoites exhibit genome-wide transcriptional changes that result in loss of gliding motility, cell traversal ability and reduction in infectivity, and, moreover, trigger metamorphosis typical of early Plasmodium intra-hepatic development. These data demonstrate that Puf2 is a key player in regulating sporozoite developmental control, and imply that transformation of salivary gland-resident sporozoites into liver stage-like parasites is regulated by a post-transcriptional mechanism.

Vesicle trafficking during sporozoite development in Plasmodium berghei: ultrastructural evidence for a novel trafficking mechanism

Oocysts from Anopheles stephensi mosquitoes fed on murine blood infected with Plasmodium berghei berghei, were fixed for electron microscopy 6-12 days post-feeding. Ultrastructural analysis focused on Golgi-related trafficking pathways for rhoptry and microneme formation during sporogony. A small Golgi complex of 1-3 cisternae is formed close to the spindle pole body from coated vesicles budded from the nuclear envelope which is confluent with the endoplasmic reticulum. Rhoptries begin as small spheroidal bodies apparently formed by fusion of Golgi-derived vesicles, lengthening to 3-4 microm, and increasing in number to 4 per sporozoite. Ultrastructural data indicate the presence of a novel mechanism for vesicle transport between the Golgi complex and rhoptries along a longitudinal 30 nm - thick fibre (rootlet fibre or tigelle). Filamentous links between vesicles and rootlet indicate that this is a previously undescribed vesicle transport organelle. Genesis of micronemes occurs late in bud maturation and starts as spheroidal dense-cored vesicles (pro-micronemes), transforming to their mature bottle-like shape as they move apically. Filamentous links also occur between micronemes and subpellicular microtubules, indicating that as in merozoites, micronemes are trafficked actively along these structures.

New exogenous stages of oocysts, sporocysts, and sporozoites of Goussia cichlidarum Landsberg and Paperna 1985 (Sporozoa: Coccidia) and impact of endogenous stages on the swim bladder of tilapias in Egypt

Obviously, the present study reports the coccidian parasite so-called Goussia cichlidarum for the first time in Egypt. Altogether, 25 exogenous stages were clearly distinguished from specimens of naturally infected fishes of Oreochromis niloticus, O. auraeus, and Tilapia zillii from different locations. The total prevalence of infection was about 41%. Mostly, infected fish grossly seemed with a healthy body, although severe lesions have been detected microscopically in massive infection. Portions of thick wall swim bladder have been placed in vitro. The released parasitic stages have been photographed, sketched, measured, described, and compared with previously described species. Oocysts, sporocysts, and sporozoites have also been differentiated morphologically and morphometrically. Maturity stages of sporozoites containing sporocysts within either an oocyst or those released and sporulated outside the oocyst were considerably discernible. In addition, endogenous stages have also been investigated in histological sections included gamonts, merozoites, oocysts, and different stages of sporozoites.

Cryoelectron tomography reveals periodic material at the inner side of subpellicular microtubules in apicomplexan parasites

Microtubules are dynamic cytoskeletal structures important for cell division, polarity, and motility and are therefore major targets for anticancer and antiparasite drugs. In the invasive forms of apicomplexan parasites, which are highly polarized and often motile cells, exceptionally stable subpellicular microtubules determine the shape of the parasite, and serve as tracks for vesicle transport. We used cryoelectron tomography to image cytoplasmic structures in three dimensions within intact, rapidly frozen Plasmodium sporozoites. This approach revealed microtubule walls that are extended at the luminal side by an additional 3 nm compared to microtubules of mammalian cells. Fourier analysis revealed an 8-nm longitudinal periodicity of the luminal constituent, suggesting the presence of a molecule interacting with tubulin dimers. In silico generation and analysis of microtubule models confirmed this unexpected topology. Microtubules from extracted sporozoites and Toxoplasma gondii tachyzoites showed a similar density distribution, suggesting that the putative protein is conserved among Apicomplexa and serves to stabilize microtubules.

Flotillin-1 localization on sporozoites oF Eimeria tenella

In an attempt to identify parasite surface components involved in the interaction with the host cell, the present research focuses on the rafts of Eimeria tenella that might be involved in the host cell invasion process. To that end, this study was undertaken to investigate the expression of flotillin-1, which is an important component and marker of lipid rafts at the plasma membrane of sporozoites of E. tenella. The expression of this plasma membrane protein was identified by an antibody that specifically reacts with flotillin- and was studied by electron microscopy. Flotillin-1 was found to occur in patches on the surface of E. tenella sporozoites. Immunoblot analysis of the total proteins of the sporozoites showed only 1 band of approximately 48 kDa. This indicates that the antibody exclusively recognized the molecules of flotillin-1 expressed on the surface of E. tenella sporozoites. The presence of flotillin-1 on the cellular membrane of sporozoites predominantly at the apical tip suggests that flotillin-1 belongs to the invasion machinery of E. tenella.

Enzymes of type II fatty acid synthesis and apicoplast differentiation and division in Eimeria tenella

Apicomplexan parasites, Eimeria tenella, Plasmodium spp. and Toxoplasma gondii, possess a homologous plastid-like organelle termed the apicoplast, derived from the endosymbiotic enslavement of a photosynthetic alga. However, currently no eimerian nuclear encoded apicoplast targeted proteins have been identified, unlike in Plasmodium spp. and T. gondii. In this study, we demonstrate that nuclear encoded enoyl reductase of E. tenella (EtENR) has a predicted N-terminal bipartite transit sequence, typical of apicoplast-targeted proteins. Using a combination of immunocytochemistry and EM we demonstrate that this fatty acid biosynthesis protein is located in the apicoplast of E. tenella. Using the EtENR as a tool to mark apicoplast development during the Eimeria lifecycle, we demonstrate that nuclear and apicoplast division appear to be independent events, both organelles dividing prior to daughter cell formation, with each daughter cell possessing one to four apicoplasts. We believe this is the first report of multiple apicoplasts present in the infectious stage of an apicomplexan parasite. Furthermore, the microgametes lacked an identifiable apicoplast consistent with maternal inheritance via the macrogamete. It was found that the size of the organelle and the abundance of EtENR varied with developmental stage of the E. tenella lifecycle. The high levels of EtENR protein observed during asexual development and macrogametogony is potentially associated with the increased synthesis of fatty acids required for the rapid formation of numerous merozoites and for the extracellular development and survival of the oocyst. Taken together the data demonstrate that the E. tenella apicoplast participates in type II fatty acid biosynthesis with increased expression of ENR during parasite growth. Apicoplast division results in the simultaneous formation of multiple fragments. The division mechanism is unknown, but is independent of nuclear division and occurs prior to daughter formation.

Experimentally induced monensin-resistant Eimeria tenella and membrane fluidity of sporozoites

Two resistant lines of Eimeria tenella (H) to monensin were developed after 35 passages in chickens medicated with 100-125 ppm or 125-200 ppm monensin in the diet. Drug sensitivity of the induced lines to different level drugs were estimated with mean lesion scores (LS), mean oocyst productions (OP), percentage optimum anticoccidial activity (POAA), reduction of lesion scores (RLS), relative oocyst production (ROP), anticoccidial index (ACI) and global index (GI), respectively. Membrane fluidity of sporozoites of the sensitive line (i.e. the parent line, coded as MON-S((S))) and two resistant lines (coded as MON-R((S))-1 and MON-R((S))-2) with and without in vitro exposure to monensin were determined. Membrane fluidity of MON-R((S))-1 and MON-R((S))-2 were significantly lower than that of MON-S((S)). In vitro exposure to monensin significantly increased membrane fluidity of MON-S((S)), but had a much less effect on those of MON-R((S))-1 and MON-R((S))-2. Sporozoits of the MON-S((S))and MON-R((S))-2 with or without in vitro exposure to monensin were examined by SEM, and the sensitive sporozoites (MON-S((S))) appeared swollen and bulgy after treatment with monensin, while there was no obvious morphological deformation in the resistant sporozoites (MON-R((S))-2). The results suggest that the altered membrane fluidity in the membranes of E. tenella may be related to the decreased sensitivity to monensin.

EIMERIA SPECIES FROM THE EUROPEAN POND TURTLE, EMYS ORBICULARIS (REPTILIA: TESTUDINES), IN GALICIA (NW SPAIN), WITH DESCRIPTION OF TWO NEW SPECIES

Parasitological examination of feces from 44 Emys orbicularis from Galicia (NW Spain) revealed the presence of 2 new eimerian species, Eimeria gallaeciaensis sp. n. and E. emydis sp. n., as well as E. mitraria (Laveran and Mesnil, 1902) Doflein, 1909. Oocysts of E. gallaeciaensis n. sp. were found in 20 of 44 (45.4%) turtles and are subspherical to lightly ovoid-ellipsoid, 19.3 x 16.0 (17-22 x 15-18) microm, shape index 1.2 (1.1-1.3), with a smooth, single-layered wall. Micropyle and polar granule are absent, but an oocyst residuum is present. Sporocysts are ellipsoid, 9.7 x 5.1 (9-10 x 5-6) microm, shape index 1.9 (1.7-2.0), each with a sporocyst residuum and a conical Stieda body usually bearing 1-4 short and thin projections. Oocysts of E. emydis n. sp. were found in the feces of 5 of 44 (11.4%) turtles and are ovoid, rarely pear-shaped, 22.6 x 17.0 (20-25 x 15.5-18) microm, shape index 1.3 (1.2-1.5), with a smooth, single-layered wall with a slight thinning at the pointed end. Micropyle and polar granule are absent, and an oocyst residuum is present. Sporocysts are ellipsoid, 11.4 x 6.0 (9-13 x 5-7) microm, shape index 1.9 (1.6-2.2), each with sporocyst residuum and a prominent Stieda body bearing 3-5 club-shaped projections. In addition to the new species described, this is the first report of E. mitraria parasitizing E. orbicularis.

Electron tomographic and ultrastructural analysis of the Cryptosporidium parvum relict mitochondrion, its associated membranes, and organelles

Sporozoites of the apicomplexan Cryptosporidium parvum possess a small, membranous organelle sandwiched between the nucleus and crystalloid body. Based upon immunolabelling data, this organelle was identified as a relict mitochondrion. Transmission electron microscopy and tomographic reconstruction reveal the complex arrangement of membranes in the vicinity of this organelle, as well as its internal organization. The mitochondrion is enveloped by multiple segments of rough endoplasmic reticulum that extend from the outer nuclear envelope. In tomographic reconstructions of the mitochondrion, there is either a single, highly-folded inner membrane or multiple internal subcompartments (which might merge outside the reconstructed volume). The infoldings of the inner membrane lack the tubular "crista junctions" found in typical metazoan, fungal, and protist mitochondria. The absence of this highly conserved structural feature is congruent with the loss, through reductive evolution, of the normal oxidative phosphorylation machinery in C. parvum. It is proposed that the retention of a relict mitochondrion in C. parvum is a strategy for compartmentalizing away from the cytosol toxic ferrous iron and sulfide, which are needed for iron sulfur cluster biosynthesis, an essential function of mitochondria in all eukaryotes.

Cryptosporidium parvum mitochondrial-type HSP70 targets homologous and heterologous mitochondria

A mitochondrial HSP70 gene (Cp-mtHSP70) is described for the apicomplexan Cryptosporidium parvum, an agent of diarrhea in humans and animals. Mitochondrial HSP70 is known to have been acquired from the proto-mitochondrial endosymbiont. The amino acid sequence of Cp-mtHSP70 shares common domains with mitochondrial and proteobacterial homologues, including 34 amino acids of an NH2-terminal mitochondrion-like targeting presequence. Phylogenetic reconstruction places Cp-mtHSP70 within the mitochondrial clade of HSP70 homologues. Using reverse transcription-PCR, Cp-mtHSP70 mRNA was observed in C. parvum intracellular stages cultured in HCT-8 cells. Polyclonal antibodies to Cp-mtHSP70 recognize a approximately 70-kDa protein in Western blot analysis of sporozoite extracts. Both fluorescein- and immunogold-labeled anti-Cp-mtHSP70 localize to a single mitochondrial compartment in close apposition to the nucleus. Furthermore, the NH2-terminal presequence of Cp-mtHSP70 can correctly target green fluorescent protein to the single mitochondrion of the apicomplexan Toxoplasma gondii and the mitochondrial network of the yeast Saccharomyces cerevisiae. When this presequence was truncated, the predicted amphiphilic alpha-helix was shown to be essential for import into the yeast mitochondrion. These data further support the presence of a secondarily reduced relict mitochondrion in C. parvum.

Nematopsis gigas n. sp. (Apicomplexa), a parasite of Nerita ascencionis (Gastropoda, Neritidae) from Brazil

A new species of Nematopsis (Apicomplexa, Porosporidae) is described from the mantle tissues of the seawater gastropod, Nerita ascencionis (Neritidae), collected in the Atlantic North off the coast of "Fernando de Noronha" Island (3 degrees 47' 57'' S, 32 degrees 25' 12'' W) situated about 350 km from the northeast coast of Brazil. Numerous oocysts, each contained in a parasitophorous vacuole, were found in the cytoplasm of phagocytes in the mantle tissue of the host. The phagocytes were surrounded by a thin wall composed of lucent material. The phagocyte cytoplasm contained a nucleus surrounded by numerous vesicles and some dense masses. The oocysts were 21.9 +/- 0.5 microm long, and 11.5 +/- 0.6 microm wide. The oocyst wall was 0.18-0.25 microm thick, and the apical zone contained a micropyle, 1.0-1.2 microm in diameter, covered by a canopy-like operculum about 0.25 microm thick. Externally, the oocyst wall was surrounded by numerous anastomosing microfibrils attached to the wall and extending towards the periphery of the parasitophorous vacuole. Some microfibrils formed a dense complex network that surrounded the oocyst in the middle of the parasitophorous vacuole, which opened only at the apical zone near the external region of the opercular system. On the basis of the data obtained by light and transmission electron microscopy and host specificity, the gregarine Nematopsis gigas is distinguished from the nearest species as a new species. The taxonomic affinities and morphological comparisons with other similar species of the same genus are discussed.

Cryptosporidium parvum Cpn60 targets a relict organelle

Chaperonin 60 (Cpn60) is a well-established marker protein for eukaryotic mitochondria and plastids. In order to determine whether the small double-membrane-bounded organelle posterior to the nucleus in the apicomplexan Cryptosporidium parvum is a mitochondrion, the Cpn60 gene of C. parvum sporozoites ( CpCpn60) was analyzed and antibodies were generated for localization of the peptide. Sequence and phylogenetic analyses indicated that CpCpn60 is a mitochondrial isotype and that antibodies against it localize to the rough endoplasmic reticulum-enveloped remnant organelle of C. parvum sporozoites. These data show this organelle is of mitochondrial origin.

Sites of interaction between aldolase and thrombospondin-related anonymous protein in plasmodium

Gliding motility and host cell invasion by apicomplexan parasites are empowered by an acto-myosin motor located underneath the parasite plasma membrane. The motor is connected to host cell receptors through trans-membrane invasins belonging to the thrombospondin-related anonymous protein (TRAP) family. A recent study indicates that aldolase bridges the cytoplasmic tail of MIC2, the homologous TRAP protein in Toxoplasma, and actin. Here, we confirm these unexpected findings in Plasmodium sporozoites and identify conserved features of the TRAP family cytoplasmic tail required to bind aldolase: a subterminal tryptophan residue and two noncontiguous stretches of negatively charged amino acids. The aldolase substrate and other compounds that bind to the active site inhibit its interaction with TRAP and with F-actin, suggesting that the function of the motor is metabolically regulated. Ultrastructural studies in salivary gland sporozoites localize aldolase to the periphery of the secretory micronemes containing TRAP. Thus, the interaction between aldolase and the TRAP tail takes place during or preceding the biogenesis of the micronemes. The release of their contents in the anterior pole of the parasite upon contact with the target cells should bring simultaneously aldolase, TRAP and perhaps F-actin to the proper subcellular location where the motor is engaged.

Opsonization by antigen-specific antibodies as a mechanism of protective immunity induced by Plasmodium falciparum circumsporozoite protein-based vaccine

Recently conducted trials involving the Plasmodium falciparum circumsporozoite (CS) protein-based RTS,S malaria vaccine yielded unprecedented protection against a challenge with infectious sporozoites (spzs). The RTS,S vaccine induced high titres of CS protein-specific antibodies (Abs) in many of the protected volunteers, but the contribution of these Abs to protection remains unknown. Because opsonization by Ab promotes the uptake and destruction of spzs by monocytes and macrophages in both rodent and primate malaria, we asked if the RTS,S-induced Abs have antigen-specific opsonizing activity. Screening plasma from a large number of subjects using spzs was impractical, therefore we developed an alternative assay based on cytofluorometry that allowed the detection of fluoresceinated-Ag-Ab complexes endocytosed by the FcR+ THP-1 human monocyte line. The results showed that plasma samples from RTS,S-immunized subjects contained opsonizing CS protein-specific Abs and the endocytic activity of these Abs in protected subjects was significantly higher than in subjects who were susceptible to infection with spzs. We also demonstrated by electron microscopy that live spzs exposed to RTS,S-immune plasma could be internalized by the THP-1 cells. These results suggest that opsonization by CS protein-specific Abs might be one of the mechanisms that contributes to RTS,S-induced protective immunity.

Myosin A tail domain interacting protein (MTIP) localizes to the inner membrane complex of Plasmodium sporozoites

Apicomplexan host cell invasion and gliding motility depend on the parasite's actomyosin system located beneath the plasma membrane of invasive stages. Myosin A (MyoA), a class XIV unconventional myosin, is the motor protein. A model has been proposed to explain how the actomyosin motor operates but little is known about the components, topology and connectivity of the motor complex. Using the MyoA neck and tail domain as bait in a yeast two-hybrid screen we identified MTIP, a novel 24 kDa protein that interacts with MyoA. Deletion analysis shows that the 15 amino-acid C-terminal tail domain of MyoA, rather than the neck domain, specifically interacts with MTIP. In Plasmodium sporozoites MTIP localizes to the inner membrane complex (IMC), where it is found clustered with MyoA. The data support a model for apicomplexan motility and invasion in which the MyoA motor protein is associated via its tail domain with MTIP, immobilizing it at the outer IMC membrane. The head domain of the immobilized MyoA moves actin filaments that, directly or via a bridging protein, connect to the cytoplasmic domain of a transmembrane protein of the TRAP family. The actin/TRAP complex is then redistributed by the stationary MyoA from the anterior to the posterior end of the zoite, leading to its forward movement on a substrate or to penetration of a host cell.

Virus-like particles in an antarctic Aggregata sp.: I. Sporogonial stages

An unknown Aggregata sp. was found in the renal organ of an antarctic Benthoctopus sp., when it was inspected for the presence of dicyemid mesozoans. Merozoites invaded the renal epithelium, whereas sporogonial stages resided in the submucosal connective tissue. Interestingly, individuals of all developmental stages were found to be infected with hitherto unknown virus-like particles. These virus-like particles, spherical in shape, nonenveloped and measuring approximately 30 nm in diameter, could be observed in the nuclei as well as within the cytoplasm. Greater amounts of virus-like particles tended to be arranged in paracrystalline arrays. Although the infection was extensive, it obviously had no pathogenic effect on the parasites themselves. On the basis of the host specificity, size, morphology and histochemical analysis, which suggested the putative viral genome as RNA, a relationship with Totoviridae is assumed.