If host is refractory, insistent parasite goes berserk: Trypanosomatid Blastocrithidia raabei in the dock bug Coreus marginatus

Here we characterized the development of the trypanosomatid Blastocrithidia raabei in the dock bug Coreus marginatus using light and electron microscopy. This parasite has been previously reported to occur in the host hemolymph, which is rather typical for dixenous trypanosomatids transmitted to a plant or vertebrate with insect's saliva. In addition, C. marginatus has an unusual organization of the intestine, which makes it refractory to microbial infections: two impassable segments isolate the anterior midgut portion responsible for digestion and absorption from the posterior one containing symbiotic bacteria. Our results refuted the possibility of hemolymph infection, but revealed that the refractory nature of the host provokes very aggressive behavior of the parasite and makes its life cycle more complex, reminiscent of that in some dixenous trypanosomatids. In the pre-barrier midgut portion, the epimastigotes of B. raabei attach to the epithelium and multiply similarly to regular insect trypanosomatids. However, when facing the impassable constricted region, the parasites rampage and either fiercely break through the isolating segments or attack the intestinal epithelium in front of the barrier. The cells of the latter group pass to the basal lamina and accumulate there, causing degradation of the epitheliocytes and thus helping the epimastigotes of the former group to advance posteriorly. In the symbiont-containing post-barrier midgut segment, the parasites either attach to bacterial cells and produce cyst-like amastigotes (CLAs) or infect enterocytes. In the rectum, all epimastigotes attach either to the cuticular lining or to each other and form CLAs. We argue that in addition to the specialized life cycle B. raabei possesses functional cell enhancements important either for the successful passage through the intestinal barriers (enlarged rostrum and well-developed Golgi complex) or as food reserves (vacuoles in the posterior end).

Recent advances on the immunobiology of Bithynia spp. hosts of Opisthorchis viverrini

This article reviews the past and present scientific reports regarding Bithynia spp. focusing on the biology, ecology and life cycle of Bithynia snails and their responses to Opisthorchis viverrini infection. Moreover, new data regarding comparative molecular genomics and proteomic approaches have recently revealed novel molecular components involved in the immune defence responses from Bithynia spp., providing additional perspectives for future studies. Studies on the specific interaction between Bithynia snails and their trematodes will contribute to further understanding the snail-parasite relationship with regards to epidemiology and control of Opisthorchiasis and broaden the scope on comparative immunology of gastropod snails.

The effect of trematode infection on the markers of oxidative stress in the offspring of the freshwater snail Lymnaea stagnalis

Most invertebrate species exhibit immunological responses that can inactivate and eliminate penetrating parasites. Such immune responses in particular involve the formation of potentially toxic reactive oxygen species (ROS). We explored the immune capabilities of the first-generation (F1) offspring of naturally infected freshwater snails, Lymnaea stagnalis, in response to infection by trematode cercariae under laboratory conditions. The rates of ROS formation and peroxidase activity in the hemolymph of the F1 offspring of L. stagnalis parents infected by an asexual stage of trematodes were significantly higher than in F1 offspring of uninfected parents. Compared to offspring from uninfected parents, the growth rate of F1 snails from infected parents was higher, but survival was lower. After infection of F1 snails by trematode cercariae of Echinoparyphium aconiatum under laboratory conditions, the rate of ROS formation and peroxidase activity in the hemolymph of F1 offspring of uninfected parents increased compared to control snails. This pattern persisted throughout the entire 3-week observation period. In contrast, the rate of ROS formation in the hemolymph of F1 snails from infected parents after experimental infection by E. aconiatum cercariae did not differ from controls, and peroxidase activity even decreased. Thus, trematode parthenitae infection of parents could alter the immune response of their offspring.

Molecular characterisation of immunological memory following homologous or heterologous challenges in the schistosomiasis vector snail, Biomphalaria glabrata

Invertebrate immune response may be primed by a current infection in a sustained manner, leading to the failure of a secondary infection with the same pathogen. The present study focuses on the Schistosomiasis vector snail Biomphalaria glabrata, in which a specific genotype-dependent immunological memory was demonstrated as a shift from a cellular to a humoral immune response. Herein, we investigate the complex molecular bases associated with this genotype-dependant immunological memory response. We demonstrate that Biomphalaria regulates a polymorphic set of immune recognition molecules and immune effector repertoires to respond to different strains of Schistosoma parasites. These results suggest a combinatorial usage of pathogen recognition receptors (PRRs) that distinguish different strains of parasites during the acquisition of immunological memory. Immunizations also show that snails become resistant after exposure to parasite extracts. Hemolymph transfer and a label-free proteomic analysis proved that circulating hemolymph compounds can be produced and released to more efficiently kill the newly encountered parasite of the same genetic lineage.

Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph

The parasitic mite Varroa destructor is the greatest single driver of the global honey bee health decline. Better understanding of the association of this parasite and its host is critical to developing sustainable management practices. Our work shows that this parasite is not consuming hemolymph, as has been the accepted view, but damages host bees by consuming fat body, a tissue roughly analogous to the mammalian liver. Both hemolymph and fat body in honey bees were marked with fluorescent biostains. The fluorescence profile in the guts of mites allowed to feed on these bees was very different from that of the hemolymph of the host bee but consistently matched the fluorescence profile unique to the fat body. Via transmission electron microscopy, we observed externally digested fat body tissue in the wounds of parasitized bees. Mites in their reproductive phase were then fed a diet composed of one or both tissues. Mites fed hemolymph showed fitness metrics no different from the starved control. Mites fed fat body survived longer and produced more eggs than those fed hemolymph, suggesting that fat body is integral to their diet when feeding on brood as well. Collectively, these findings strongly suggest that Varroa are exploiting the fat body as their primary source of sustenance: a tissue integral to proper immune function, pesticide detoxification, overwinter survival, and several other essential processes in healthy bees. These findings underscore a need to revisit our understanding of this parasite and its impacts, both direct and indirect, on honey bee health.

Microsporidian Parasites Found in the Hemolymph of Four Baikalian Endemic Amphipods

At present, approximately 187 genera and over 1300 species of Microsporidia have been described, among which almost half infect aquatic species and approximately 50 genera potentially infect aquatic arthropods. Lake Baikal is the deepest and one of the oldest lakes in the world, and it has a rich endemic fauna with a predominance of arthropods. Among the arthropods living in this lake, amphipods (Crustacea) are the most dominant group and are represented by more than 350 endemic species. Baikalian amphipods inhabit almost all depths and all types of substrates. The age and geographical isolation of this group creates excellent opportunities for studying the diversity, evolution and genetics of host-parasite relationships. However, despite more than 150 years of study, data investigating the microsporidia of Lake Baikal remain incomplete. In this study, we used molecular genetic analyses to detect microsporidia in the hemolymph of several endemic species of amphipods from Lake Baikal. We provide the first evidence that microsporidian species belonging to three genera (Microsporidium, Dictyocoela and Nosema) are present in the hemolymph of Baikalian endemic amphipods. In the hemolymph of Eulimnogammarus verrucosus, we detected SSU rDNA of microsporidia belonging to the genus Nozema. In the hemolymph of Pallasea cancellous, we found the DNA of Microsporidium sp. similar to that in other Baikalian endemic amphipods; Dictyocoela sp. was found in the hemolymph of Eulimnogammarus marituji and Acanthogammarus lappaceus longispinus.

[Homoxenous trypanosomatids from true bugs Pyrrhocoris apterus (L.) in the north of the Pskov region]

In the north of the Pskov region (58 degrees 35' N, 28 degrees 55' E) the appearance of a single colony of true bugs Pyrrhocoris apterus has been recorded. Dissection of 95 individuals from this colony revealed 100% prevalence of infection with homoxenous trypanosomatids. In 3% of the cases intestinal infection was accompanied by hyperinvasion into the salivary glands and hemolyph of the hosts. Analysis of trypanosomatid morphotypes demonstrated mixed infections in all studied P. apterus individuals. At least 4 forms of promastigotes along with epimastigotes, choanomastigotes and amastigotes were found. The distribution of the trypanosomatid morphotypes over all intestinal parts as well as salivary glands and hemolymph was investigated. Three isolates of the flagellates were deposited into the living cultures collection of the laboratory of Protozoology of the Zoological institute of the Russian Academy of Sciences.

Ecology of Rhodnius robustus Larrousse, 1927 (Hemiptera, Reduviidae, Triatominae) in Attalea palm trees of the Tapajós River Region (Pará State, Brazilian Amazon)

BACKGROUND

The rising number of acute cases of Chagas disease in the State of Pará, reported in the past two decades, has been associated, in part, with the ingestion of juice of local palm tree fruits, mainly açaí berry and bacaba. Near the study area, in Santarém, Pará State, an outbreak of Chagas disease has been notified and investigations suggest the consumption of bacaba juice as the main source of infection with T. cruzi. The purpose of this study is to assess the aspects associated to the ecology of Rhodnius robustus in palm trees of three communities of the Tapajós region, in the State of Pará, Brazil.

METHODS

Palm trees were cut down and dissected to search for triatomines. DNA from triatomines was extracted to investigate natural infection by Trypanosoma cruzi and T. rangeli. For statistical analyzes, data from infestation of palm trees, as well as the rates of natural infection by T. cruzi and T. rangeli were compared by Chi-square test. Triatomine density values were analyzed by the nonparametric Kruskal Wallis test and then comparisons between each pair of variables were made by the Mann-Whitney test assuming a confidence interval of 95%.

RESULTS

We dissected 136 palm trees, 60 at the end of the rainy period and 76 at the end of the dry period. Seventy-three of them (53.7%) were infested with triatomines and three species were found, namely: Rhodnius robustus, Rhodnius pictipes and Panstrongylus lignarius. We collected 743 triatomines, and R. robustus was predominant (n = 739). The identification of natural infection of the insects by trypanosomatids revealed that 125 triatomines were infected by T. cruzi, 69 by T. rangeli and 14 presented both parasites, indicating the presence of mixed infection in the same vector.

CONCLUSION

The results suggest that São Tomé is the community with greater density of triatomines and infestation of palm trees; also, it demonstrates the existence of an intense sylvatic cycle in the region, which demands intensive surveillance to prevent human transmission.

Melanotic pathology and vertical transmission of the gut commensal Elizabethkingia meningoseptica in the major malaria vector Anopheles gambiae

Background

The resident gut flora is known to have significant impacts on the life history of the host organism. Endosymbiotic bacterial species in the Anopheles mosquito gut are potent modulators of sexual development of the malaria parasite, Plasmodium, and thus proposed as potential control agents of malaria transmission.

Results

Here we report a melanotic pathology in the major African malaria vector Anopheles gambiae, caused by the dominant mosquito endosymbiont Elizabethkingiameningoseptica. Transfer of melanised tissues into the haemolymph of healthy adult mosquitoes or direct haemolymph inoculation with isolated E. meningoseptica bacteria were the only means for transmission and denovo formation of melanotic lesions, specifically in the fat body tissues of recipient individuals. We show that E. meningoseptica can be vertically transmitted from eggs to larvae and that E. meningoseptica-mono-associated mosquitoes display significant mortality, which is further enhanced upon Plasmodium infection, suggesting a synergistic impact of E. meningoseptica and Plasmodium on mosquito survival.

Conclusion

The high pathogenicity and permanent association of E. meningoseptica with An. Gambiae through vertical transmission constitute attractive characteristics towards the potential design of novel mosquito/malaria biocontrol strategies.

An impossible journey? The development of Plasmodium falciparum NF54 in Culex quinquefasciatus

Although Anopheles mosquitoes are the vectors for human Plasmodium spp., there are also other mosquito species-among them culicines (Culex spp., Aedes spp.)-present in malaria-endemic areas. Culicine mosquitoes transmit arboviruses and filarial worms to humans and are vectors for avian Plasmodium spp., but have never been observed to transmit human Plasmodium spp. When ingested by a culicine mosquito, parasites could either face an environment that does not allow development due to biologic incompatibility or be actively killed by the mosquito's immune system. In the latter case, the molecular mechanism of killing must be sufficiently powerful that Plasmodium is not able to overcome it. To investigate how human malaria parasites develop in culicine mosquitoes, we infected Culex quinquefasciatus with Plasmodium falciparum NF54 and monitored development of parasites in the blood bolus and midgut epithelium at different time points. Our results reveal that ookinetes develop in the midgut lumen of C. quinquefasciatus in slightly lower numbers than in Anopheles gambiae G3. After 30 hours, parasites have invaded the midgut and can be observed on the basal side of the midgut epithelium by confocal and transmission electron microscopy. Very few of the parasites in C. quinquefasciatus are alive, most of them are lysed. Eight days after the mosquito's blood meal, no oocysts can be found in C. quinquefasciatus. Our results suggest that the mosquito immune system could be involved in parasite killing early in development after ookinetes have crossed the midgut epithelium and come in contact with the mosquito hemolymph.

Glycotope sharing between snail hemolymph and larval schistosomes: larval transformation products alter shared glycan patterns of plasma proteins

Recent evidence supports the involvement of inducible, highly diverse lectin-like recognition molecules in snail hemocyte-mediated responses to larval Schistosoma mansoni. Because host lectins likely are involved in initial parasite recognition, we sought to identify specific carbohydrate structures (glycans) shared between larval S. mansoni and its host Biomphalaria glabrata to address possible mechanisms of immune avoidance through mimicry of elements associated with the host immunoreactivity. A panel of monoclonal antibodies (mABs) to specific S. mansoni glycans was used to identify the distribution and abundance of shared glycan epitopes (glycotopes) on plasma glycoproteins from B. glabrata strains that differ in their susceptibilities to infection by S. mansoni. In addition, a major aim of this study was to determine if larval transformation products (LTPs) could bind to plasma proteins, and thereby alter the glycotopes exposed on plasma proteins in a snail strain-specific fashion. Plasma fractions (< 100 kDa/> 100 kDa) from susceptible (NMRI) and resistant (BS-90) snail strains were subjected to SDS-PAGE and immunoblot analyses using mAB to LacdiNAc (LDN), fucosylated LDN variants, Lewis X and trimannosyl core glycans. Results confirmed a high degree of glycan sharing, with NMRI plasma exhibiting a greater distribution/abundance of LDN, F-LDN and F-LDN-F than BS-90 plasma (< 100 kDa fraction). Pretreatment of blotted proteins with LTPs significantly altered the reactivity of specific mABs to shared glycotopes on blots, mainly through the binding of LTPs to plasma proteins resulting in either glycotope blocking or increased glycotope attachment to plasma. Many LTP-mediated changes in shared glycans were snail-strain specific, especially those in the < 100 kDa fraction for NMRI plasma proteins, and for BS-90, mainly those in the > 100 kDa fraction. Our data suggest that differential binding of S. mansoni LTPs to plasma proteins of susceptible and resistant B. glabrata strains may significantly impact early anti-larval immune reactivity, and in turn, compatibility, in this parasite-host system.

Cross-effects of nickel contamination and parasitism on zebra mussel physiology

Aquatic organisms are exposed to pollution which may make them more susceptible to infections and diseases. The present investigation evaluated effects of nickel contamination and parasitism (ciliates Ophryoglena spp. and intracellular bacteria Rickettsiales-like organisms), alone and in combination, on biological responses of the zebra mussel Dreissena polymorpha, and also the infestation abilities of parasites, under laboratory controlled conditions. Results showed that after 48 h, more organisms were infected in nickel-exposed groups, which could be related to weakening of their immune system. Acting separately, nickel contamination and infections were already stressful conditions; however, their combined action caused stronger biological responses in zebra mussels. Our data, therefore, confirm that the parasitism in D. polymorpha represents a potential confounding factor in ecotoxicological studies that involve this bivalve.

Effects of Plasmodium gallinaceum on hemolymph physiology of Aedes aegypti during parasite development

Insect disease vectors show diminished fecundity when infected with Plasmodium. This phenomenon has already been demonstrated in laboratory models such as Aedes aegypti, Anopheles gambiae and Anopheles stephensi. This study demonstrates several changes in physiological processes of A. aegypti occurring upon infection with Plasmodium gallinaceum, such as reduced ecdysteroid levels in hemolymph as well as altered expression patterns for genes involved in vitellogenesis, lipid transport and immune response. Furthermore, we could show that P. gallinaceum infected A. aegypti presented a reduction in reproductive fitness, accompanied by an activated innate immune response and increase in lipophorin expression, with the latter possibly representing a nutritional resource for Plasmodium sporozoites.

A pathogenic parasite interferes with phagocytosis of insect immunocompetent cells

Phagocytosis activity of hemocytes of the host Galleria mellonella (Lepidoptera) was modulated by the infection of the entomopathogenic nematode Steinernema feltiae (Rahbditida) and was found to be correlated with the opsonization of bacteria by hemolymph factors. The presence of nematodes resulted in a significative decrease in phagocytosis of bacteria by host hemocytes, both in in vivo and in in vitro assays. Host interacting proteins (HIPs), which appear to function as opsonic factors and are essential to perform immune responses, were removed by S. feltiae from host hemolymph, by means of its epicuticle binding properties. Host humoral factors sequestered by the parasite have been identified by monodimensional and 2D electrophoretic analysis. The data suggest that S. feltiae, living in association with symbiontic bacteria (Xenorhabdus nematophilus), develop an immune suppressive strategy to support its bacteria, which diminished the effectiveness of immunological surveillance by the host.

Transcripts analysis of the entomopathogenic nematode Steinernema carpocapsae induced in vitro with insect haemolymph

Steinernema carpocapsae is an insect parasitic nematode widely used in pest control programs. The efficacy of this nematode in controlling insects has been found to be related to the pathogenicity of the infective stage. In order to study the parasitic mechanisms exhibited by this parasite, a cDNA library of the induced S. carpocapsae parasitic phase was generated. A total of 2500 clones were sequenced and 2180 high-quality ESTs were obtained from this library. Cluster analysis generated a total of 1592 unique sequences including 1393 singletons. About 63% of the unique sequences had significant hits (e</=1e-05) to the non-redundant protein database. The remaining sequences most likely represent putative novel protein coding genes. Comparative analysis identified 377 homologs in C. elegans, 431 in C. briggsae and 75 in other nematodes. Classification of the predicted proteins revealed involvement in diverse cellular, metabolic and extracellular functions. One hundred and nineteen clusters were predicted to encode putative secreted proteins such as proteases, proteases inhibitors, lectins, saposin-like proteins, acetylcholinesterase, anti-oxidants, and heat-shock proteins, which can possibly have host interactions. This dataset provides a basis for genomic studies towards a better understanding of the events that occur in the parasitic process of this entomopathogenic nematode, including invasion of the insect haemocoelium, adaptations to insect innate immunity and stress responses, and production of virulence factors. The identification of key genes in the parasitic process provides useful tools for the improvement of S. carpocapsae as a biological agent.

Could hosts considered as low quality for egg-laying be considered as high quality for host-feeding?

When parasitoid females encounter a host, they can either lay an egg and thus invest in current reproduction or feed on the host and thus invest in future reproduction. However, hosts could have different values according to their parasitized status. Whereas already parasitized hosts represent poor quality for egg-laying, they could have a high nutritive value for feeding. Moreover, the optimal strategy adopted generally depends on the females' physiological state. In this study, the impact of the females' physiological state on their reproductive strategies was investigated in the solitary parasitoid Anisopteromalus calandrae. We analysed how their age and diet influenced (i) the use of hosts (feeding vs. oviposition) and (ii) host selection (previously parasitized vs. unparasitized). Our results show that both age and diet influence the reproductive strategy of A. calandrae females: old females fed with the poorer diet laid fewer eggs and made more host-feeding than others. Females also showed a preference for already parasitized hosts for feeding. This strategy cannot be explained by the nutritive value of haemolymph, as parasitized hosts carry fewer lipids. However, as parasitized hosts are also paralyzed, it could be less costly to feed on them than on unparasitized hosts.

Transmission of the parasitic dinoflagellate Hematodinium sp. infection in blue crabs Callinectes sapidus by cannibalism

Infection with the parasitic dinoflagellate Hematodinium sp. can be devastating to blue crab Callinectes sapidus populations. Morbidity and mortality appear to depend on the burden of parasitic organisms. Heavily infected crabs become lethargic and, if not preyed upon, succumb to overwhelming infection. We report on the transmission of Hematodinium sp. into blue crabs that were fed pieces of infected tissues and examined for evidence of infection at time periods from 1 to 48 h and for the general state of their health after 4 d. During the first 16 h after feeding, Hematodinium sp. was found in the gut, followed by large increases in hemolymph hemocytes and the appearance of hemocytic nodules in tissues. By 16 h, the hemocytic nodules appeared poorly circumscribed and disorganized. No nodules were seen in a heavily infected crab after 24 h. By the end of the 48 h after feeding, 73% (11 of 15) of the crabs had shown evidence of infection with Hematodinium sp. Those crabs with infection intensities (Hematodinium sp. as percent of cells in hemolymph) higher than 20% were dead within 4 d.

A new ovine Babesia species transmitted by Hyalomma anatolicum anatolicum

The pathogenicity and morphology of a large Babesia species, Babesia sp. Xinjiang, are described here. The parasite has very low virulence for sheep, and caused no detectable clinical symptoms. Splenectomized sheep infected with the parasite showed mild fever and low parasitemia and would recover gradually. If splenectomized sheep were immuno-suppressed with dexamethasone, the parasitemia could reach 8.5%, and death occurred. A splenectomized calf could not be infected with the Babesia species. Paired parasites were the typical form of the Babesia species in erythrocytes and the average size of a pair of parasites was 2.42 (+/-0.35) microm x 1.06 (+/-0.22) microm. Merozoites were found in the gut, salivary gland, haemolymph, ovary and eggs of female Hyalomma anatolicum anatolicum engorged on sheep infected with the parasites. The results of experimental transmission showed that the larval, nymph and adult stages of H. a. anatolicum could transmit the Babesia species to sheep.

Protein markers of Marteilia sydneyi infection in Sydney rock oysters, Saccostrea glomerata

Marteilia sydneyi is the causative agent of QX disease in Sydney rock oyster, Saccostrea glomerata. It is responsible for disease outbreaks among oysters that occur during summer and can result in up to 95% mortality. QX disease has significantly decreased S. glomerata production in some areas of Australia's eastern seaboard over the past 30 years. Marteilia sydneyi sporulates in the digestive gland of oysters leading to complete disorganization of the infected tissues. The current study used proteomics to identify potential molecular markers of sporulating M. sydneyi infection during a field trial undertaken in the Georges River, Sydney, between December 2006 and May 2007. Early stages of M. sydneyi infection were detected by polymerase chain reaction, whilst cytological examination was used to identify sporulating M. sydneyi in the gut. Protein expression in oyster haemolymph was assessed during the M. sydneyi infection period by two dimensional electrophoresis. Proteome maps identified significant differences in the expression of four proteins in oysters with sporulating M. sydneyi infections.

The microneme proteins CTRP and SOAP are not essential for Plasmodium berghei ookinete to oocyst transformation in vitro in a cell free system

BACKGROUND

Two Plasmodium berghei ookinete micronemal proteins, circumsporozoite and TRAP related protein (CTRP) and secreted ookinete adhesive protein (SOAP) both interact with the basal lamina component laminin. Following gene disruption studies it has been proposed that, apart from their role in motility, these proteins may be required for interactions leading to ookinete-to-oocyst transformation.

METHODS

CTRP and SOAP null mutant P. berghei ookinetes were compared to P. berghei ANKA wild-type for their ability to transform and grow in vitro. To confirm in vitro findings for P. berghei CTRP-KO ookinetes were injected into the haemocoel of Anopheles gambiae female mosquitoes.

RESULTS

Transformation, growth, and viability were comparable for the gene disrupted and wild-type parasites. P. berghei CTRP-KO ookinetes were able to transform into oocysts in the haemocoel of An. gambiae mosquitoes.

CONCLUSION

Neither CTRP nor SOAP is required for parasite transformation in vitro. By-passing the midgut lumen allows for the transformation of P. berghei CTRP-KO ookinetes suggesting that it is not required for transformation in vivo.

Phenoloxidase-associated cellular defence in the Sydney rock oyster, Saccostrea glomerata, provides resistance against QX disease infections

The enzyme phenoloxidase is a critical component of the immunological defence of invertebrates. Previously, we have shown that the activity of phenoloxidase in Sydney rock oysters (Saccostrea glomerata) correlates with the severity of QX disease outbreaks. The aetiological agent of QX disease is the opportunistic protozoan parasite, Marteilia sydneyi. In this study, we examined the response of oyster haemocytes to challenge with M. sydneyi. Granular haemocytes were able to rapidly phagocytose parasite sporonts. Phagocytosis stimulated intracellular associated phenoloxidase activity that led to the complete melanisation of phagosomes. Significant differences in phagocytic indexes and phenoloxidase activities were observed between oysters selected for resistance to QX disease (QXR) and non-selected wild-type oysters. The data suggest that phagocytosis and cellular melanisation are critical defensive responses of Sydney rock oysters infected with M. sydneyi.

Identification of two down-regulated genes in entomopathogenic nematode Heterorhabditis bacteriophora infective juveniles upon contact with insect hemolymph

Entomopathogenic nematode Heterorhabditis bacteriophora infective juveniles (IJs) employ multiple strategies to combat with insect innate immune system after invasion. We employed suppressive subtractive hybridization (SSH) technique to study the gene expression in the IJs upon contact with the insect hemolymph in vitro. We identified two clones having higher expression levels in the IJs than IJs treated with insect hemolymph. The differential expression levels were confirmed by Northern blot hybridization with reference to the constitutive expression level of Heterorhabditis bacteriophora actin2 gene. Clone HbGPS11.C1G02 encoded a phosphofructokinase (PFK) with a 2.5 kb transcript and clone HbGPS11.C4C08 corresponded to a 2.1 kb transcript encoding a protein that had weak similarity to trans-sialidase from Trypanosoma cruzi. The differential expression of PFK in H. bacteriophora IJs before and during recovery process represented a switch from active movement in search of insect hosts to a state of combating insect innate immune system. This first report of H. bacteriophora differential gene expression provides a glimpse at the gene expression profile of H. bacteriophora IJ recovery process.

Immunolocalization of Schistosoma mansoni and Schistosoma haematobium antigens reacting with their Egyptian snail vectors

The reaction of the haemolymph and the tissue of infected intermediate hosts, Biomphalaria alexandrina and Bulinus truncatus to Schistosoma mansoni and S. haematobium antigens were investigated using the indirect immunoperoxidase technique. A new technique, Agarose cell block was used in collection of haemolymph which helped in collecting plenty of well formed cells in comparison to the ordinary one using the cytospin. Collected haemolymph and prepared tissues of uninfected and infected B. alexandria and B. truncatus were fixed and then reacted with anti-S. mansoni and anti-S. haematobium IgG polyclonal antibodies. The haemolymph and tissue of infected B. alexandrina and B. truncatus gave a positive peroxidase reaction represented by a brown colour. In haemolymph, the positive peroxidase reaction was detected mainly in the cytoplasm of the amoebocytes. In the tissue, it was detected in epithelial cells lining the tubules, male cells in the lumen of the tubules and in female oogonia cells along the periphery of the tubules. The similarity in the strength and distribution of positive reaction in B. alexandrina and B. truncates was observed as compared to control. Thus, the immunoperoxidase technique proved to be an effective indicator for the schistosome-antigen in the snails.

Pathology of Hematodinium infections in snow crabs (Chionoecetes opilio) from Newfoundland, Canada

Bitter crab disease (BCD) of snow crabs, Chionoecetes opilio, is caused by a parasitic dinoflagellate, Hematodinium sp. The disease has shown an alarming increase in prevalence in the commercial fishery in eastern and northeastern areas of Newfoundland and Labrador since it was first recorded there in the early 1990s. We documented histopathological alterations to the tissues in snow crabs with heavy infections of Hematodinium sp. and during sporulation of the parasite. Pressure necrosis was evident in the spongy connective tissues of the hepatopancreas and the blood vessels in most organs. In heavy infections, little remained of the spongy connective tissues around the hepatopancreas. Damage to the gills varied; in some cases it was severe, particularly during sporulation, involving apparent thinning of the cuticle, loss of epithelial cells, and fusion of the membranous layers of adjacent gill lamellae. Affected lamellae exhibited varying degrees of distention with a loss of trabecular cells, hemocyte infiltrations, and swelling or "clubbing" along the distal margins. Large numbers of zoospores were located along the distal margins of affected lamellae suggesting that sporulation may cause a lysis or bursting of the thin lamellar cuticle, releasing spores. Pressure necrosis, due to the build up of high densities of parasites, was the primary histopathological alteration in most tissues. Hematodinium infections in the snow crab are chronic, long-term infections that end in host death, during sporulation of the parasite.

Susceptibility of different triatomine species to Trypanosoma rangeli experimental infection

Trypanosoma rangeli is a kinetoplastid protozoan parasite that has been found in the majority of Latin American countries, overlapping its distribution area with that of Trypanosoma cruzi, the causative agent of Chagas disease. This parasite shares the same reservoirs and vectors as T. cruzi. Triatomines from genus Rhodnius are considered the most susceptible hosts to infection. In this work, we report the susceptibility of different triatomine species (Rhodnius neglectus, Panstrongylus megistus, Triatoma infestans, T. sordida, T. braziliensis, and T. vitticeps) to experimental infection by T. rangeli isolated from Didelphis albiventris in a highly endemic region for Chagas disease. An intense parasitism was evidenced in feces (56% to 81%) of the majority of the species studied on the 10th day after infection, decreasing during the period of the experiment (30 days). T. vitticeps did not present parasites in feces at any time. All triatomine species presented parasites in the hemolymph. In T. vitticeps and P. megistus, this parasitism was scarce (6.3% and 6.6%, respectively). In the other species, the parasitism was variable (62.5% to 100%). Triatomine mortality varied between 3% to 40%, increasing during the infection in all species studied. The lowest mortality was observed for T. infestans. Also, we showed that only trypomastigotes forms from salivary glands, and hemolymph were infective for mice. We conclude that all triatomine species used were susceptible to infection by T. rangeli at different levels. There was no direct correlation between intensity of parasitism and mortality.

LIFE CYCLE OF HEPATOZOON CANIS (APICOMPLEXA: ADELEORINA: HEPATOZOIDAE) IN THE TICK RHIPICEPHALUS SANGUINEUS AND DOMESTIC DOG (CANIS FAMILIARIS)

The life cycle of the apicomplexan protozoon Hepatozoon canis in its natural hosts Rhipicephalus sanguineus (tick) and Canis familiaris (domestic dog) was studied in an experimental infection. Tick nymphs were fed on a naturally infected dog, or they were infected by percutaneous injection of blood. Dogs were inoculated by ingestion of adult ticks containing mature oocysts. Gamonts were in syzygy 24 hr after percutaneous injection of ticks. Early oocysts were detected 96 hr after nymph repletion, and mature oocysts in adult ticks were infective to dogs 40 days postmolt. Merogony was detected in dog bone marrow from 13 days postinoculation (PI) and included meronts containing 20-30 micromerozoites, and a second type with 2-4 macromerozoites. Monozoic cysts were observed in the spleen in conjunction with merogony. Gamontogony with infection of leukocytes by micromerozoites occurred from 26 days PI, and gamont parasitemia, which completed the life cycle, was detected 28 days PI. The length of the life cycle from nymphal attachment to parasitemia in dogs was 81 days. Increased body temperatures were evident from 16 to 27 days PI and paralleled the time of intensive bone marrow merogony. Skeletal pain and recumbency were manifested in 2 dogs. This study further elucidates the life cycle of H. canis and provides a sequential morphologic description of H. canis merogony, gamontogony, and sporogony.

A contribution to the pathobiology of Biomphalaria glabrata hemocytes

This study attempts to investigate the relationship between the hemocytes in the two compartments: circulating peripheral lymph and the connective tissues. The hemocytes are compared with the vertebrate macrophages and constitute the principal line of defense against external aggression. The hemocytes were counted in circulating hemolymph and their phagocytic capability was evaluated in Schistosoma mansoni-infected Biomphalaria glabrata and the results were compared with those obtained from normal intact control snails. Although the number of circulating hemocytes revealed a mild increase in snails at the 6th week of infection, the overall findings were similar and pointed out that the cells in the two compartments are not functionally connected. However, the hemocytes found within the connective tissues of infected snails showed definite ultrastructural differences in the number and disposition of cytoplasmic prolongations and organelles in comparison with the hemocytes from non-infected snails. Histochemically, the staining for acid phosphatase activity served as a marker to hemocytes, sometimes being found in extracellular material at the foci of parasite-hemocyte interactions.

Lectin from the Manila Clam Ruditapes philippinarum Is Induced upon Infection with the Protozoan Parasite Perkinsus olseni

Glycan-binding proteins (lectins) are widely expressed in many invertebrates, although the biosynthesis and functions of the lectins are not well understood. Here we report that Manila clam (Ruditapes philippinarum) synthesizes a lectin termed Manila clam lectin (MCL) upon infection with the protozoan parasite Perkinsus olseni. MCL is synthesized in hemocytes as a approximately 74-kDa precursor and secreted into hemolymph where it is converted to 30- and 34-kDa polypeptides. The synthesis of MCL in hemocytes is stimulated by one or more factors in Perkinsus-infected hemolymph, but not directly by Perkinsus itself. MCL can bind to the surfaces of purified hypnospores and zoospores of the parasite, and this binding is inhibitable by either EDTA or GalNAc. Fluorescent beads coated with purified MCL were actively phagocytosed by hemocytes from the clam. Immunohistochemistry showed that secreted MCL is concentrated within cyst-like structures. To define the glycan binding specificity of MCL we examined its binding to an array of biotinylated glycans. MCL recognizes terminal non-reducing beta-linked GalNAc as expressed within the LacdiNAc motif GalNAcbeta1-4GlcNAcbeta1-R and glycans with terminal, non-reducing beta-linked Gal residues. Our results show that the synthesis of MCL is specifically up-regulated upon parasite infection of the clams and may serve as an opsonin through recognition of terminal GalNAc/Gal residues on the parasites.

Using green fluorescent malaria parasites to screen for permissive vector mosquitoes

Background

The Plasmodium species that infect rodents, particularly Plasmodium berghei and Plasmodium yoelii, are useful to investigate host-parasite interactions. The mosquito species that act as vectors of human plasmodia in South East Asia, Africa and South America show different susceptibilities to infection by rodent Plasmodium species. P. berghei and P. yoelii infect both Anopheles gambiae and Anopheles stephensi, which are found mainly in Africa and Asia, respectively. However, it was reported that P. yoelii can infect the South American mosquito, Anopheles albimanus, while P. berghei cannot.

Methods

P. berghei lines that express the green fluorescent protein were used to screen for mosquitoes that are susceptible to infection by P. berghei. Live mosquitoes were examined and screened for the presence of a fluorescent signal in the abdomen. Infected mosquitoes were then examined by time-lapse microscopy to reveal the dynamic behaviour of sporozoites in haemolymph and extracted salivary glands.

Results

A single fluorescent oocyst can be detected in live mosquitoes and P. berghei can infect A. albimanus. As in other mosquitoes, P. berghei sporozoites can float through the haemolymph and invade A. albimanus salivary glands and they are infectious in mice after subcutaneous injection.

Conclusion

Fluorescent Plasmodium parasites can be used to rapidly screen susceptible mosquitoes. These results open the way to develop a laboratory model in countries where importation of A. gambiae and A. stephensi is not allowed.

Temporal association of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) and bacteria

Galleria mellonella L. larvae were infected with three species (seven strains) of Steinernema spp. or three species (three strains) of Heterorhabditis spp. Infected larvae were incubated at 22, 27, and 32 degrees C. Larvae were dorsally dissected every 6h over a 48-h period. Hemolymph was collected and streaked on tryptic soy agar plates. Several non-symbiotic bacterial species were identified from infected insect cadavers: Enterobacter gergoviae, Vibrio spp., Pseudomonas fluorescens type C, Serratia marcescens, Citrobacter freundii, and Serratia proteomaculans. At 18-24 h incubation, the nematode-associated symbiont occurred almost exclusively. Bacterial associates generally appeared outside the 18-24 h window. Infective juveniles of Steinernema feltiae (Filipjev) (27), Steinernema riobrave Cabanillas, Poinar, and Raulston (Oscar), or Steinernema carpocapsae (Weiser) (Kapow) were left untreated, or surface sterilized using thimerosal, then pipetted under sterile conditions onto tryptic soy agar plates. Several additional species of associated bacteria were identified using this method compared with the less extensive range of species isolated from infected G. mellonella. There was no difference in bacterial species identified from non-sterile or surface sterilized nematodes, suggesting that the bacteria identified originated from either inside the nematode or between second and third stage juvenile cuticles. Infective juveniles of S. feltiae (Cowles), S. carpocapsae (Cowles), and H. bacteriophora Poinar (Cowles) were isolated from field samples. Nematodes were surface-sterilized using sodium hypochlorite, mixed with G. mellonella hemolymph, and pipetted onto Biolog BUG (with blood) agar. Only the relevant symbionts were isolated from the limited number of samples available. The nematodes were then cultured in the laboratory for 14 months (sub-cultured in G. mellonella 7-times). Other Enterobacteriaceae could then be isolated from the steinernematid nematodes including S. marcescens, Salmonella sp., and E. gergoviae, indicating the ability of the nematodes to associate with other bacteria in laboratory culture.

Pathogenesis of Helicosporidium sp. (Chlorophyta: Trebouxiophyceae) in susceptible noctuid larvae

Helicosporidium sp. is a unique, achlorophyllous green alga that has been reported to infect various insect orders, including Lepidoptera, Diptera, and Coleoptera. The infectious cyst stage is ingested by the host, ruptures in the midgut lumen, and releases a filamentous cell. Histopathological examinations using larvae of a susceptible noctuid host, Spodoptera exigua, showed both cysts and filamentous cells affiliated with the microvillar lining of the midgut epithelium. A considerable proportion of the ingested cysts (22-39%) were recovered in feces collected 24 h after ingestion. A small number of filamentous cells passed the midgut epithelium and entered the hemocoel within 4-24 h after cyst ingestion. After 48 h, vegetative cell stages were detected in the hemolymph, followed by a 4- to 5-day period of increasing multiplication. Cyst differentiation in the colonized hemolymph began 6-7 days after the treatment.

Towards an understanding of the interactions of Trypanosoma cruzi and Trypanosoma rangeli within the reduviid insect host Rhodnius prolixus

This review outlines aspects on the developmental stages of Trypanosoma cruzi and Trypanosoma rangeli in the invertebrate host, Rhodnius prolixus. Special attention is given to the interactions of these parasites with gut and hemolymph molecules and the effects of the organization of midgut epithelial cells on the parasite development. The vector insect's permissiveness to T. cruzi, which develops in the vector gut, largely depends on the host nutritional state, the parasite strain and the molecular interactions with trypanolytic compounds, lectins and resident bacteria in the gut. T. rangeli invades the hemocoel and once in the hemolymph, can be recognized and activates the defense system of its insect vector, i.e., the prophenoloxidase system, phagocytosis, hemocyte microaggregation, superoxide and nitric oxide activity and the eicosanoid biosynthesis pathway. Taken together, these findings not only provide a better understanding of the interactions parasite-insect vector, but also offer new insights into basic physiological processes involved in the parasites transmission.

A review of the parasitic dinoflagellates Hematodinium species and Hematodinium-like infections in marine crustaceans

Parasitic dinoflagellates in the genus Hematodinium are important parasites of marine Crustacea. Outbreaks of these parasites have damaged commercial stocks of Norway lobster Nephrops norvegicus, snow crab Chionoecetes opilio, Tanner crab C. bairdi, American blue crab Callinectes sapidus, and velvet swimming crab Necora puber. Species of Hematodinium can reach high enough levels to regulate their host populations, but mortalities are also centred on the unfished juveniles and females, hosts not normally sampled by fisheries; hence impacts are often underreported. Seasonal prevalences of up to 85 % occur annually in many host populations; in effect, these parasites form cryptic blooms in the water column with crabs and other crustaceans at risk of disease. We review the biology and ecology of Hematodinium spp. infections in crustaceans. Included is a comparison of the different infections, a synthesis of what is known, and an attempt to highlight fruitful areas for continued research.

Babesia spp. infection in Boophilus microplus engorged females and eggs in São Paulo State, Brazil

Babesia spp. infections were investigated in Bos taurus x Bos indicus dairy cows and calves and in Boophilus microplus engorged female ticks and eggs. Blood samples and engorged female ticks were collected from 25 cows and 27 calves. Babesia spp. was detected in ticks by microscopic examination of hemolymph of engorged female and by squashes of egg samples. Cattle infection was investigated in blood thin smears and by DNA amplification methods (PCR and nested PCR), using specific primers for Babesia bovis and Babesia bigemina. Merozoites of B. bovis (3 animals) and B. bigemina (12 animals) were detected exclusively in blood smears of calves. DNA amplification methods revealed that the frequency of B. bigemina infection in calves (92.6%) and in cows (84%) and of B. bovis in calves (85.2%) and in cows (100%) did not differ significantly (P > 0.05). Babesia spp. infection was more frequent in female ticks and eggs collected from calves (P < 0.01) than from cows, especially in those which had patent parasitemia. Hatching rates of B. microplus larvae were assessed according to the origin of engorged females, parasitemia of the vertebrate host, frequency and intensity of infection in engorged female tick, and frequency of egg infection. Hatching rate was lower in samples collected from calves (P < 0.01) than from cows, and in those in which Babesia spp. was detected in egg samples (P < 0.01).

Inhibition of hemocyte microaggregation reactions in Rhodnius prolixus larvae orally infected with Trypanosoma rangeli

Hemocoelic inoculation of epimastigotes of Trypanosoma rangeli strain H14 into 5th-instar larvae of Rhodnius prolixus previously fed on blood containing the same parasites, showed reduced number of hemocyte microaggregates in the hemolymph, enhanced number of flagellates in the hemolymph as well as increased mortality of these insects. All these effects were counteracted by combined inoculation of R. prolixus with T. rangeli and arachidonic acid. In vitro assays using hemolymph taken from insects previously fed on blood containing parasites showed that hemocyte microaggregation reactions were also attenuated when T. rangeli is used as inducer of the reaction, and that simultaneous applying T. rangeli with arachidonic counteracted the hemocyte microaggregation inhibition. We suggest that arachidonic acid pathway can be a mediator of hemocyte microaggregation reactions in the hemolymph of insects inoculated with T. rangeli, and that oral infection with this protozoan inhibits the release of arachidonic acid.

[Microsporidiosis in the wax moth Galleria mellonella (Lepidoptera: Pyralidae) caused by Vairimorpha ephestiae (Microsporidia: Burenellidae)]

An experimental microsporidiosis of the wax moth caterpillars from laboratory population had been caused by oral infecting of early stages larvae and by intracavity injections of the spores of the microsporidian species Vairimorpha ephestiae. Peculiarities of microsporidiosis proceeding, manifestations of host defence reactions, and also an effect of the temperature of caterpillars cultivation and conditions of spores keeping on liability of the insects to the infection were studied. The effect of the microsporidia on the host organism was the early death or the delay of larvae development, but in several cases external manifestations of the effect of the parasite on the host were absent. The development of the parasites from the moment of infecting to the appearing of the mature spores congestions in the host organism proceeded 6 days. Microsporidia invaded insect fat body and caused its hypertrophy and disappearance of lipid granules. In the intestine and salivary glands microsporidia were not observed in the period from 6 to 16 day of the development. On the final stage of microsporidiosis the all contents of fatty tissue cells were replaced by spores of microsporidia. Under microscope only diplocaryotic spores of the Nozema type had been found in infected and died specimens, but not octospores. The spores threw out polar tubes under the change of pH in incubating solution from neutral to alkaline. The effects of microsporidiosis on the wax moth haemolymph were the increased rate of prohaemocytes, appearing of multinuclear free-circulating cells at 6 day after infection, and suppression of the reaction of haemolymph melanization with the mass sporogenesis of the parasite. The characteristic symptom of the wax moth microsporidiosis had been revealed, accumulation of black points and small spots of irregular form under cuticle ("reaction of attretization"). Increase of the temperature of insect cultivation up to 32 degrees C during 3 days after infection contributed to the full deliverance of the insects from the infection in first and second generations. It can be considered as a method of treatment of wax moth laboratory colonies from microsporidiosis. Oral infection of III and IV stage caterpillars by the spores being kept during 3-6 months under 4 degrees C in form of water suspension caused the death of 63.0-61.5 and 91% of caterpillars being cultivated under 25 and 21 degrees C respectively. Under the temperature of cultivation equal 30 degrees C the mortality did not differ from the control sample (8-10%). The spores extracted from dried bodies of caterpillars lost their vitality. It was demonstrated by the test on infectious ability in vivo and by acridine orange staining. This host-parasite system appears to be perspective in investigations of resistance mechanisms in insects and immunosuppressive features of entomopathogen microsporidia.

Haemolymph parasite of the shore crab Carcinus maenas: pathology, ultrastructure and observations on crustacean haplosporidians

A protozoan parasite with some features of haplosporidians is described from the European shore crab Carcinus maenas. The parasite establishes a systemic infection through the haemal sinuses and connective tissues. Intracellular stages of the parasite were found within reserve inclusion, connective tissue, and muscle cells, while free forms were present in all haemal spaces. A uninucleate stage appeared to develop to a multinucleate plasmodial stage following multiple mitotic divisions of the nucleus. Histopathology also indicated that nuclear division may occur to form multinucleate plasmodia, in connective tissue, reserve inclusion and muscle cells, the multinucleate plasmodium being enclosed in the host-cell plasma membrane. It appears that the multinucleate plasmodium may then undergo internal cleavages which result in plasmodial fragmentation to form many uninucleate stages. Both stages, but particularly the uninucleate stage, contained cytoplasmic, large, ovoid, dense vesicles (DVs), some of which contained an internal membrane separating the medulla from the cortex, as in haplosporosomes. Golgi-like cisternae, closely associated with the nuclear membrane, formed DVs and haplosporosome-like bodies (HLBs), superficially resembling viruses. Infrequently, HLBs may condense to form haplosporosomes. The DVs, as in spores of some Haplosporidium spp. and paramyxeans, may give rise to, and are homologous with, haplosporosomes. Other features, such as the presence of an intranuclear mitotic spindle, lipid droplets, and attachment of DVs and haplosporosomes to the nuclear membrane, indicate that the C. maenas parasite is a haplosporidian. A similar organism reported from the haemolymph of spot prawns Pandalus spp., and haplosporidians reported from prawns Penaeus vannamei and crabs Callinectes sapidus may belong to this group. It is concluded that the well-characterised haplosporidians of molluscs and some other invertebrates may not be characteristic of the whole phylum, and that morphologically and developmentally similar organisms may also be haplosporidians, whether they have haplosporosomes or not.

Further morphological studies on the behavior of Trypanosoma rangeli in the hemocytes of Rhodnius prolixus

The hemocytes of Rhodnius prolixus were analyzed during the course of infection with the protozoan Trypanosoma rangeli. The following cell types were identified: prohemocyte, plasmatocyte, adipocyte, granular cell and oenocytoid. The number of these cells changes during the infection course thus indicating a cell response to infection of R. prolixus by T. rangeli. Transmission electron microscopy showed that plasmatocytes were able to ingest epimastigote forms of the parasite, which were then found within a parasitophorous vacuole. Amorphous material was seen within the vacuole suggesting that fusion of host cell lysosomes with the vacuole took place. Intravacuolar parasites in process of digestion were observed. In addition, reaction product indicative of the presence of acid phosphatase was observed in parasite-containing vacuoles. No dividing parasites were seen within the vacuole in contrast to what was observed outside the host cells.

Sources of spores for the possible horizontal transmission of Thelohania solenopsae (Microspora: Thelohaniidae) in the red imported fire ants, Solenopsis invicta

We screened adult and larval secretions and midden piles for the presence of Thelohania solenopsae spores to decipher potential sources for the horizontal transmission of the pathogen in fire ants. Hemolymph samples from both adult and larvae were also screened to rule out hemolymph contamination of samples. In adults, Thelohania spores were found in the crop and the fecal fluids, although only free spores were found in the fecal fluids of adults. In fourth instar larvae, both free and octospores were seen in midgut and the meconium samples. All of the midden pile samples had T. solenopsae spores of both types. Based on these results, we theorize that the pathogen may be horizontally transmitted within a colony by the removal and sharing of meconium of prepupating fourth instar larvae by adult workers and by the adult fecal droppings, and intercolonially by contamination of midden piles or brood raiding.

Comparison of light microscopic techniques for the diagnosis of the infection of the European flat oyster Ostrea edulis by the protozoan Bonamia ostreae

A comparison among various histological techniques for the detection of the parasite Bonamia ostreae in oysters Ostrea edulis was performed to evaluate their sensitivity and suitability for different purposes. The comparison involved examination of histological sections, tissue imprints from gills, digestive gland, gonad and heart, and haemolymph cell monolayers, prepared through various protocols. Every technique produced some false negative. The haemolymph cell monolayers were more sensitive than tissue imprints and histological sections. Heart imprints provided the highest sensitivity among tissue imprints. Examination of histological sections was among the least sensitive techniques. Four procedures for estimation of infection intensity were compared. Some differences in accuracy for the estimation of infection intensity between haemolymph cell monolayers and histological sections (HS) were detected: there was a very good agreement when the infection appeared low or heavy in HS but it was not so good in the remaining cases. The results suggest the need for a critical review of the recommendations of the "Office Internationale des Epizooties" and the European Union for diagnosis of bonamiosis.

Silica treatment increases the susceptibility of the Cabo Frio strain of Biomphalaria tenagophila to Schistosoma mansoni infection but does not alter the natural resistance of the Taim strain

The present work demonstrates that silica treatment represents a suitable in vivo method to evaluate the role of host phagocytic hemocytes in the mechanisms of resistance to parasitic infection. Silica inoculation into Biomphalaria tenagophila snail induced a significant reduction in the circulating hemolymph granulocytes in both strains tested (Taim and Cabo Frio). The granulocyte reduction was accompanied by a significant increase in the number of circulating dead cells. In B. tenagophila Cabo Frio, silica treatment enhanced snail susceptibility to Schistosoma mansoni, shortening the intramolluskan phase of the parasite and increasing the number of sporocysts and cercariae produced. In B. tenagophila Taim, the same treatment did not abrogate natural resistance to S. mansoni reported for this snail strain. These in vivo results demonstrate that macrophage-like granulocytes are involved in the mechanism of S. mansoni sporocyst destruction in Cabo Frio snails and suggest that another, different mechanism may be responsible to the natural resistance of B. tenagophila Taim.

Differential phenoloxidase activity between native and invasive gammarids infected by local acanthocephalans: differential immunosuppression?

Manipulative endoparasites can alter the behaviour and the physiology of their intermediate hosts in ways that increase the probability of successful transmission to the final host. This requires that the parasite is able to circumvent its host's immune defence. Successful immune evasion may depend on host-parasite coevolutionary history and the appearance of new hosts invading the local host population may promote local parasite maladaptation. To test this hypothesis, we examined the effect of 2 acanthocephalan parasites, Pomphorhynchus laevis and Polymorphus minutus, on the immunity of their local and new invasive gammarid intermediate hosts, respectively Gammarus pulex and Gammarus roeseli. We found that infection by each parasite was correlated with a decrease, at different degrees, of the standing level of immune defence in local hosts--measured as the phenoloxidase (PO) enzyme activity--whereas invasive hosts infected by P. laevis had their PO-enzyme activity enhanced. These results suggest that these acanthocephalans evade their local host immune response through immunosuppression but cannot evade the immune response of their new invasive host. The potential role of this maladaptation on the success of invasive species is discussed.

Co-infection by a yeast-like organism in Hematodinium-infected European edible crabs Cancer pagurus and velvet swimming crabs Necora puber from the English Channel

During the winter months, edible crabs Cancer pagurus and velvet swimming crabs Necora puber from the English Channel can harbour infections by a Hematodinium sp. dinoflagellate. This parasite is responsible for a highly pathological condition known as 'Pink Crab Disease' (PCD) in the edible crab. In the current study, a high proportion (between 25 and 100%) of Hematodinium-infected edible and velvet swimming crabs captured from 2 sites in the English Channel also harboured a systemic infection by a yeast-like organism. This is the first report of such an infection in crabs. Budding yeast-like cells were observed intracellularly in circulating haemocytes and free in the host plasma. These cells stained positively with silver and periodic acid-Schiff (PAS) reactions. Despite an apparent haemocytopoenia in Hematodinium-infected crabs, haemocytic encapsulation of yeast-like cells was evident, while no such response was observed against Hematodinium sp. plasmodia. It is hypothesised that Hematodinium infection in these crabs may either increase the likelihood of secondary infections via an indirect suppression of the host immune system, or alternatively, decrease the likelihood of competitive growth inhibition by stimulating the host immune system to encapsulate and destroy secondary pathogens. Results are discussed with regard to the likely identity of the yeast-like organism, and the role of secondary pathogens in the eventual mortality of Hematodinium-infected hosts.

Monitoring the prevalence of the parasitic dinoflagellate Hematodinium sp. in snow crabs Chionoecetes opilio from Conception Bay, Newfoundland

Bitter crab disease (BCD) of snow crabs Chionoecetes opilio is caused by a parasitic dinoflagellate, Hematodinium sp. In Newfoundland's commercial fishery, infected snow crabs are identified using visual, macroscopic signs of disease for separation prior to processing. We estimated the sensitivity and specificity of gross, macroscopic diagnosis of Hematodinium sp. by comparing these results with microscopic examination of prepared hemolymph smears. The sensitivity of a diagnostic test is the probability that the test will yield a positive result given that the animal has the disease. The specificity is the probability of a negative result given the animal is not diseased. In October 1998, we conducted a design-based survey using cluster sampling in 2 strata. Over 10 000 snow crabs from pot and trawl surveys were examined macroscopically for BCD. In addition, over 350 crabs were randomly examined microscopically for disease. The double sampling resulted in an estimated sensitivity of 52.7% and an estimated specificity of 100%. That is, a positive result from macroscopic examination is definitive, if the observer is well trained, but macroscopic examination will fail to detect infections in crabs with borderline clinical signs of disease. The prevalence estimated from macroscopic observations (p(st) = 2.24%) was corrected for misclassification by dividing p(st) by the estimated sensitivity (0.527), giving a corrected estimate of 4.25%. The use of double sampling provides for efficient estimation of prevalence in that large numbers of crabs can be quickly examined for gross signs of infection and the results corrected for misclassification based on a limited number of observations with a better, but time-consuming test. In addition, the prevalence of macroscopically infected male crabs was lower in a trap survey (0.57%) compared to a trawl survey (1.59%). In the trawl survey, female crabs had a significantly higher prevalence of macroscopically diagnosed infections than males (6.34%). The prevalence of BCD has shown an alarming increase since it was first detected in Newfoundland during the early 1990s. Transmission and mortality studies are warranted to better understand the effect of the disease on its commercially important host.

Continuous in vitro culture of the carpet shell clam Tapes decussatus protozoan parasite Perkinsus atlanticus

Continuous in vitro cultures of the clam Tapes decussatus parasite Perkinsus atlanticus were established from infected gill fragments, infected haemolymph and parasite hypnospores isolated from infected gill fragments following incubation in Ray's fluid thioglycollate medium (RFTM). No continuous cultures could be initiated from P. atlanticus zoospores. Cultures initiated from hypnospores yielded the highest percentage of continuous cultures (100%, 6/6), followed by cultures initiated from gill fragments (93%, 43/46) and from haemolymph (30%, 3/10). Failures to establish continuous cultures were due to microbial contamination. The source of parasite influenced the success rate, the time taken to establish cultures and the size of cultured cells. In vitro proliferation of parasite cells was mainly by vegetative multiplication. Zoosporulation, yielding motile biflagellated zoospores, was observed at a low frequency (< 1% of dividing cells) in every culture. Morphology of cultured cells examined with light and transmission electron microscopy corresponded to that of P. atlanticus found in clam tissues. Cultured cells enlarged in RFTM and stained blue-black with Lugol's solution, which are characteristics of the Perkinsus species cells. DNA sequences of the internal transcribed spacer (ITS) region of the ribosomal RNA gene complex matched those of P. atlanticus. All cultures were established in a medium designated JL-ODRP-2A that was similar in composition to the culture medium JL-ODRP-1 originally used to propagate Perkinsus marinus in vitro. Proliferation of P. atlanticus in vitro could be supported by the commercial culture medium (1:2 v/v) DME:Ham's F-12 with fetuin.

Hemocyte types and total and differential counts in unparasitized and parasitized Anastrepha obliqua (Diptera, Tephritidae) larvae

The hemocyte types, in addition to total and differential hemocyte counts were studied in parasitized and unparasitized Anastrepha obliqua larvae at the beginning and at the end of the third instar. In both developmental phases, in parasitized and unparasitized larvae, prohemocytes, plasmatocytes, granulocytes, adipohemocytes, spherulocytes and oenocytoids cells were observed. Mitotic figures indicate prohemocytes as stem cells. Prohemocytes, plasmatocytes and granulocytes are the most numerous cells in the hemolymph of A. obliqua. Difference in the total number of hemocytes was observed between unparasitized and parasitized larvae at the end of the third instar, but not at the beginning.

Removal of Toxoplasma gondii oocysts from sea water by eastern oysters (Crassostrea virginica)

Toxoplasma gondii infections have been reported in a number of marine mammals. Presently it is not known how these animals acquire T. gondii from their aquatic environment. The eastern oyster, Crassostrea virginica, has been shown to remove Cryptosporidiwn oocysts from seawater and a similar phenomenon may be occurring with T. gondii oocysts and marine invertebrates. The present study was done to determine if eastern oysters could remove and retain T. gondii oocysts from seawater. Oocysts of the VEG strain of T. gondii (1 x 10(6) oocysts) were placed in seawater (32 ppt NaCl) containing live eastern oysters. The infected seawater was removed one day postinoculation (PI) and replaced with fresh seawater. Selected oysters were removed at 1, 3 and 6 days PI. Hemolymph, gill washes, and oyster tissue were collected separately at each observation time. The oyster tissue was homogenized and all 3 samples fed separately to mice. Toxoplasma gondii positive mice were observed at each time period. The results indicate that T. gondii oocysts can be removed from seawater by eastern oysters and retain their infectivity. Contaminated raw oysters may serve as a source of T. gondii infection for marine mammals and humans.

Severe apicomplexan infection in the oyster Ostrea chilensis: a possible predisposing factor in bonamiosis

Histological examination of 6455 oysters Ostrea chilensis from Foveaux Strait south of New Zealand over a 5 yr period showed >85% contained apicomplexan zoites, irrespective of season. Zoites occurred around the haemolymph sinuses and the digestive diverticulae at all intensities of infection; occurrence in the sub-epithelium, Leydig tissue and gills/mantle increased with increasing intensity of infection. Many (>35%) oysters were heavily infected, and most of them had severely damaged tissues. Heavy infections affected gametogenesis; 1% of lightly infected oysters had empty gonad follicles lacking germinal epithelium compared with 2% of moderately infected oysters and 9% of heavily infected oysters. Of oysters with empty gonad follicles, 75% were heavily infected with zoites. The parasite spread from the haemolymph sinuses and moved between Leydig cells, causing their dissociation and lysis. Some zoites were intracellular in Leydig cells. Lesions contained many haemocytes phagocytosing zoites, leading to haemocyte lysis and causing a haemocytosis. Fibrosis occurred to repair lesions in a few oysters. The zoites had a typical apical complex with 2 polar rings and 84 sub-pellicular microtubules. Prevalence and intensity of concurrent Bonamia exitiosus infection was related to the intensity of zoite infection, with only 3.8% of B. exitiosus infections occurring in the absence of zoites, 20.0% occurring in light zoite infections, 30.9% in moderate zoite infections, and 45.4% when oysters were heavily infected with zoites. The converse was not the case, as 75.3% of zoite infections occurred in the absence of B. exitiosus infection, including 51.1% of moderate to heavy zoite infections. There was a statistically significant association between intensities of B. exitiosus and of zoites (p < 0.0001). Zoites may increase the susceptibility of oysters to B. exitiosus by occupying and destroying haemocytes, and by destroying connective tissue cells and utilising host glycogen reserves. The parasite may be heteroxenous, with other stages in the terebellid polychaete Pseudopista rostrata.

The symbiont Capsaspora owczarzaki, nov. gen. nov. sp., isolated from three strains of the pulmonate snail Biomphalaria glabrata is related to members of the Mesomycetozoea

While investigating the resistance of some strains of Biomphalaria glabrata to infection with Schistosoma mansoni, a unicellular eukaryotic symbiont was noted in the snail haemolymph. It was similar in appearance to Nuclearia sp. reported from B. glabrata. Sequences comprising the 18S, ITS1, 5.8S, ITS2 and the beginning of the 28S rDNA gene regions were obtained from symbionts isolated from three strains of B. glabrata, and compared with the same sequences obtained from a culture of Nuclearia sp. 18S rDNA sequences were identical for all four isolates. 18S rDNA sequences were used in a phylogenetic analysis to produce minimum evolution, maximum parsimony, maximum likelihood and Bayesian trees. All four analyses indicated that the B. glabrata symbiont is not closely related to Nuclearia but instead to the Mesomycetozoea, a recently recognised clade of symbiotic eukaryotes. Based on phylogenetic analysis, life history and morphological differences, the symbiont is described as a new genus and species, Capsaspora owczarzaki. Distinguishing characters are the presence of life cycle stage(s) that occur within snail haemolymph; ability to kill and ingest digenetic trematode larvae; ability to undergo asexual fission to produce daughter cells; absence of flagella, a mucous sheath and membranes containing chitin, elastin, or collagen; and presence of long unbranching pseudopodia and a penetration process. Using both polymerase chain reaction (PCR) and culturing techniques, the S. mansoni-resistant Salvador and 13-16-R1 strains were found to be significantly more likely to harbour the symbiont than the susceptible M line strain. Small but consistent sequence differences were noted among symbiont isolates from different snail strains, raising the possibility that the symbiont has diverged in different snail lineages. This suggests further that the symbiont is not restricted to albino lab-reared snails. A role, if any, of the symbiont in resistance awaits further study.