Biological and immunological characteristics of Trichinella pseudospiralis

Distribution of Trichinella spiralis, Trichinella britovi, and Trichinella pseudospiralis in the Diaphragms and T. spiralis and T. britovi in the Tongues of Experimentally Infected Pigs

There is little or even no data in the global literature on the distribution of different species of Trichinella in the individual parts of the diaphragms and tongues in infected pigs. This is of particular importance from the food safety point of view and for the conduct of routine testing of pig carcasses for Trichinella as well as epidemiological surveys. Therefore, the aim of the present study was to evaluate the distribution of Trichinella spiralis (T. spiralis), Trichinella britovi (T. britovi), and Trichinella pseudospiralis (T. pseudospiralis) ML in various parts of the diaphragm (the pillars, costal, and sternal part) and the distribution of encapsulated species of Trichinella (T. spiralis and T. britovi) in various parts of the tongues (the tip, body, and root) of experimentally infected pigs. The diaphragm pillars were the most heavily parasitized part of the diaphragm both in groups of pigs infected with particular species of Trichinella and in groups of pigs presenting different levels of infection; however, statistical differences were observed only in the group of pigs with moderate (21–35 larvae per gram-lpg) or moderately high (35–55 lpg) intensity of Trichinella spp. infection in the entire diaphragm. In all groups of pigs, regardless of the infecting Trichinella species or infection level, larvae showed a homogeneous distribution on both sides of the diaphragm and excluding those of T. pseudospiralis, also in all three parts of the tongue. Histological examination showed features of a differential inflammatory response around larvae of the different Trichinella species. This study confirmed that for mandatory examination of pig carcasses using a pooled-sample digestion assay in which each pig is intended to be represented by a 1 gram sample taken from the diaphragm pillars, if that tissue is not available, the mass of the sample taken from the remaining diaphragm parts (costal or sternal) should be at least double that from the pillars. Histological findings confirmed that the inflammatory pattern of pig muscles varies depending on the Trichinella species triggering the infection and is less intense in the case of infections with T. pseudospiralis than in infections with encapsulated species of Trichinella (T. spiralis and T. britovi).

Immuno-proteomic analysis of Trichinella spiralis, T. pseudospiralis, and T. papuae extracts recognized by human T. spiralis-infected sera

The present study explored potentially immunogenic proteins of the encapsulated (Trichinella spiralis) and non-encapsulated (T. pseudospiralis, T. papuae) species within the genus Trichinella. The somatic muscle larval extracts of each species were subjected to immunoblotting analysis using human T. spiralis-infected serum samples. Fifteen reactive bands of all three species were selected for further protein identification by liquid chromatography-tandem mass spectrometry, and their possible functions were ascertained using the gene ontology. Our findings showed immunogenic protein patterns with molecular mass in the range of 33-67 kDa. Proteomic and bioinformatic analysis revealed a wide variety of functions of 17 identified proteins, which are associated with catalytic, binding, and structural activities. Most proteins were involved in cellular and metabolic processes that contribute in the invasion of host tissues and the larval molting processes. The parasite proteins were identified as actin-5C, serine protease, deoxyribonuclease-2, and intermediate filament protein ifa-1. This information may lead to alternative tools for selection of potential diagnostic protein markers or aid in the design of vaccine candidates for prevention and control of Trichinella infection.

Trichinella inflammatory myopathy: host or parasite strategy?

The parasitic nematode Trichinella has a special relation with muscle, because of its unique intracellular localization in the skeletal muscle cell, completely devoted in morphology and biochemistry to become the parasite protective niche, otherwise called the nurse cell. The long-lasting muscle infection of Trichinella exhibits a strong interplay with the host immune response, mainly characterized by a Th2 phenotype.

The aim of this review is to illustrate the role of the Th2 host immune response at the muscle level during trichinellosis in different experimental models, such as knock-out or immuno-modulated mice. In particular, in knock-out mice a crucial role of IL-10 is evident for the regulation of inflammation intensity.

The muscular host immune response to Trichinella is partially regulated by the intestinal phase of the parasite which emphasizes the intensity of the following muscle inflammation compared with animals infected by synchronized injections of newborn larvae. In eosinophil-ablated mice such as PHIL and GATA-- animals it was observed that there was an increased NOS2 expression in macrophages, driven by higher IFN-γ release, thus responsible for muscle larva damage.

Besides modulation of the intestinal stage of the infection, using recombinant IL-12, increases the muscular parasite burden delaying adult worm expulsion from the intestine. Furthermore, a Th1 adjuvant of bacterial origin called Helicobacter pylori neutrophil activating protein (HP-NAP), administered during the intestinal phase of trichinellosis, alters the Th2 dependent response at muscle level.

All these data from the literature delineate then a mutual adaptation between parasite and host immune response in order to achieve a strategic compromise between two evolutionary forces pointed towards the survival of both species.

Evaluation of inflammatory responses against muscle larvae of different Trichinella species by an image analysis system

The aim of this study was to evaluate the inflammatory response in the muscle tissue against Trichinella larvae of encapsulated (T. spiralis, T. britovi) and non-encapsulated (T. pseudospiralis) species. The inflammatory response was estimated in histological sections of muscle tissues from Trichinella-infected CD1 mice by a newly developed method. Nuclei were stained with one fluorescent probe, which binds nucleic acids with high affinity, and fluorescence was analysed by a software program. Evaluation of the relative fluorescence units was performed in both peri-capsular (close to the nurse cell-parasite complex) and extra-capsular (where the parasite was not visible) areas. The increase in the number of nuclei in the muscle tissues of Trichinella-infected mice was considered an inflammation marker, since uninfected muscles show low nucleus density. In order to evaluate differences in the nitrosylation pattern between encapsulated (T. spiralis, T. britovi) and non-encapsulated (T. pseudospiralis, Trichinella papuae, Trichinella zimbabwensis) species, L(1) larvae were tested by immunoblotting with an anti-nitrotyrosine polyclonal antibody. Inflammation induced by T. spiralis larvae in muscle tissues is statistically higher than that elicited by the other species, both in peri- and extra-capsular areas. Nitrosylation occurs at a higher level in encapsulated than in non-encapsulated species. The method developed in this work allows demonstration of differences in the host inflammatory response against encapsulated and non-encapsulated Trichinella species.

Systematics and epidemiology of trichinella

In this review, we describe the current knowledge on the systematics, ecology and epidemiology of Trichinella and trichinellosis, and the impact of recent research discoveries on the understanding of this zoonosis. The epidemiology of this zoonosis has experienced important changes over the past two decades, especially with regard to the importance of the sylvatic cycle and the sylvatic species. Outbreaks of trichinellosis due to Trichinella spiralis from domestic swine, while still frequent, increasingly are caused by other Trichinella spp. infecting hosts such as horses, dogs, wild boars, bears and walruses. The latter revelations have occurred as a result of a series of discoveries on the systematics of Trichinella spp., facilitated by new molecular tools. As a consequence, the genus is now composed of two clades, an encapsulated group (five species and three genotypes) and a non-encapsulated one (three species). This has sparked renewed investigations on the host range of these parasites and their epidemiological features. Most dramatic, perhaps, is the recognition that reptiles may also serve as hosts for certain species. This new knowledge base, in addition to having an important relevance for food safety policies and protection measures, is raising important questions on the phylogeny of Trichinella spp., the ecological characteristics of the species and their geographic histories. Answers to these questions may have great value for the understanding of the evolutionary biology for other parasitic helminths, and may increase the value of this genus as models for research on parasitism in general.

Comparative analysis of the excretory-secretory proteome of the muscle larva of Trichinella pseudospiralis and Trichinella spiralis

The nematodes Trichinella spiralis and Trichinella pseudospiralis are both intracellular parasites of skeletal muscle cells and induce profound alterations in the host cell resulting in a re-alignment of muscle-specific gene expression. While T. spiralis induces the production of a collagen capsule surrounding the host-parasite complex, T. pseudospiralis exists in a non-encapsulated form and is also characterised by suppression of the host inflammatory response in the muscle. These observed differences between the two species are thought to be due to variation in the proteins excreted or secreted (ES proteins) by the muscle larva. In this study, we use a global proteomics approach to compare the ES protein profiles from both species and to identify individual T. pseudospiralis proteins that complement earlier studies with T. spiralis. Following two-dimensional gel electrophoresis, tandem mass spectrometry was used to identify the peptide spots. In many cases identification was aided by the determination of partial peptide sequence from selected mass ions. The T. pseudospiralis spots identified included the major secreted glycoproteins and the secreted 5'-nucleotidase. Furthermore, two major groups of T. spiralis-specific proteins and several T. pseudospiralis-specific proteins were identified. Our results demonstrate the value of proteomics as a tool for the identification of ES proteins that are differentially expressed between Trichinella species and as an aid to identifying key parasite proteins that are involved in the host-parasite interaction. The value of this approach will be further enhanced by data arising out the current T. spiralis genome sequencing project.

Developmental regulation and secretion of nematode-specific cysteine-glycine domain proteins in Trichinella spiralis

The muscle larva of Trichinella spiralis is an intracellular parasite of mammalian skeletal muscle, encapsulating within a portion of the myofiber and resulting in muscle de-differentiation. Parasite-derived factors secreted or excreted by the muscle larva are thought to play a role in the formation of the host-parasite complex and in the induction of changes in the host cell. We screened a library enriched for T. spiralis-specific cDNAs and identified a clone encoding a protein with similarity to a predicted secreted or extracellular Caenorhabditis elegans protein. The region of similarity included a conserved cysteine-glycine (CCG) domain, which we have identified as being nematode-specific. This domain is present in the predicted T. spiralis protein, Ts-CCG-1, and in a second protein, Ts-CCG-2, which we identified from subsequent analysis. We showed that while the Ts-ccg-1 gene is constitutively expressed, Ts-ccg-2 gene expression is restricted to the muscle L1 larva. Both predicted proteins contain an N-terminal signal peptide and we subsequently confirmed by MALDI-TOF mass spectrometric analyses of excretory/secretory peptide spots excised from two-dimensional gels that Ts-CCG-2 is secreted.

Up-regulation of the 31 kDa dehydroascorbate reductase in the modified skeletal muscle cell (nurse cell) during Trichinella spp. infection

Ascorbic acid (AA) is an important factor of defence against oxidative stress. AA is maintained in the reduced functional form by glutathione (GSH)-dependent dehydroascorbate (DHA) reducing enzymes, including the cytosolic glutaredoxin, the microsomal protein disulphide isomerase, and a DHA reductase of 31 kDa, hereafter referred to as DHAR, purified from rat liver cytosol and human red cells. As these mechanisms have rarely been studied in parasites, we looked for the possible presence of this 31 kDa protein in Trichinella spiralis L(1) larvae. Biochemical data, immunoblot analysis and immunohistochemical studies suggested the absence of this protein within parasites at this stage. However, they possess a low DHA reducing ability, which is probably due to the presence of glutaredoxin. On the other hand, immunohistochemical studies performed in histological sections of muscle tissue from Trichinella-infected animals showed an increase in DHAR in the nurse cell (NC) of T. spiralis- and Trichinella britovi-infected animals, compared with the surrounding muscle fibres. This result was confirmed by immunoblot analysis, whereas no such increase was observed in Trichinella pseudospiralis-infected animals. In the modified skeletal muscle cell also haeme oxygenase 1 increased, as well as lipoperoxidised proteins. Both findings suggest an oxidative stress of the NC, which might be related to the intense inflammatory reaction which surrounds the NC-parasite complex. Another possibility to explain the increase in DHAR could be that the NC needs to recycle a substantial amount of AA to synthesise the collagen capsule.

Variation and immunity to intestinal worms

Genetically determined variation in host capacity to express resistance to a given parasite plays a major role in determining the outcome of infection. It can be assumed that the same is true of variation in parasites, but very much less is known of its influence on the host-parasite relationship. Phenotypic and genotypic variation within species of intestinal worms is now well documented, detailed studies having been made of parasites such as Ascaris in humans and trichostrongyles in domestic animals. However, the extent to which this variation affects the course of infection or the host immune response in these hosts is limited. Of the nematodes used as experimental models in laboratory rodents, detailed data on phenotypic or genotypic variation are limited to Strongyloides and Trichinella. Parasite variation is known to be subject to host-mediated selection, the emergence of anthelmintic resistance being a good example. Repeated passage has been used to select lines of parasite that survive in abnormal hosts or which show adaptation to host immunity. Experimental studies with Trichinella genotypes in mice have demonstrated the extent to which parasite variation influences the nature and degree of the host's immune and inflammatory responses, the complex interplay between immunogenicity and pathogenicity influencing both partners in the relationship. Recent studies with isolates of Trichuris muris have shown how parasite variation influences the capacity of mice to express the T helper cell responses necessary for resistance. Molecular differences between T. muris isolates have been shown in their excreted/secreted products as well as at the level of their DNA. Knowledge of the functional consequences of parasite variation will add to our understanding of host-parasite evolution as well as providing a rational basis for predicting the outcome of controls strategies that rest on the improvement of host resistance through vaccination or selective breeding.

Trichinella zimbabwensis n.sp. (Nematoda), a new non-encapsulated species from crocodiles (Crocodylus niloticus) in Zimbabwe also infecting mammals

Since 1995, Trichinella larvae have been detected in 39.5% of farmed crocodiles (Crocodylus niloticus) in Zimbabwe. Morphological, biological, biochemical and molecular studies carried out on one isolate from a farmed crocodile in 2001 support the conclusion that this parasite belongs to a new species, which has been named Trichinella zimbabwensis n.sp. This species, whose larvae are non-encapsulated in host muscles, infects both reptiles and mammals. The morphology of adults and larvae is similar to that of Trichinella papuae. Adults of T. zimbabwensis cross in both directions with adults of T. papuae (i.e. male of T. zimbabwensis per female of T. papuae and male of T. papuae per female of T. zimbabwensis), producing F1 offspring which produce very few and less viable F2 larvae. Muscle larvae of T. zimbabwensis, like those of T. papuae, do not infect birds. Three allozymes (of a total of 10) are diagnostic between T. zimbabwensis and T. papuae, and five are diagnostic between T. zimbabwensis and Trichinella pseudospiralis, the third non-encapsulated species. The percentage of the pairwise alignment identity between T. zimbabwensis and the other Trichinella species for the cytochrome oxidase subunit I gene, the large subunit ribosomal-DNA (mt-lsrDNA) gene and the expansion segment five, shows that T. zimbabwensis is more similar to the two non-encapsulated species T. papuae (91% for cytochrome oxidase I; 96% for mt-lsrDNA; and 88% for expansion segment five) and T. pseudospiralis (88% for cytochrome oxidase I; 90% for mt-lsrDNA; and 66-73% for expansion segment five) than to any of the encapsulated species (85-86% for cytochrome oxidase I; 88-89% for mt-lsrDNA; and 71-79% for expansion segment five). This is the first non-encapsulated species discovered in Africa. The finding of a new Trichinella species that infects both reptiles and mammals suggests that the origin of Trichinella parasites dates back further than previously believed and can contribute to understanding the phylogeny and the epidemiology of the genus Trichinella.

The effect of Trichinella spiralis infection on the mechanical properties of the mammalian diaphragm

Trichinella spiralis larvae infect and develop within skeletal muscle cells causing major changes to their mechanical properties. The aim of this investigation was to determine the effects of T. spiralis on the power output and fatigue resistance of the mammalian diaphragm under conditions simulating in vivo operation and to relate these to respiratory performance. Infection with T. spiralis leads to major reductions in mechanical stress, work, power output and fatigue resistance. These changes are associated with the number of larvae present in the muscle and the duration of infection. However, the initial decline in mechanical performance occurs during the onset of infection when there are few larvae observed within the muscle cells, indicating that T. spiralis may affect the properties of muscle before encapsulation. This may correspond to the host's inflammatory response and the effects of larval excretory/secretory products. The decline in mechanical performance will have a profound effect on respiration both at rest and during exertion. This must influence the behaviour of the host and increase its chance of capture by predators, which is likely to benefit the parasite by facilitating its transmission.

Trichinella isolates: parasite variability and host responses

The genus Trichinella has the widest geographical distribution and the largest range of host species of all parasitic nematodes. It remains a significant human pathogen. More than 300 isolates of the genus are now available for laboratory study. The taxonomy of the genus, which has only recently achieved some stability, depends upon the use of a variety of biological, biochemical and genetic criteria. The biological characteristics of isolates, particularly those relating to infectivity and pathogenicity, can show considerable variation because they are subject to strong host influences, notably those associated with immune and inflammatory responses. Comparative studies of different isolates in different hosts, particularly strains of inbred mice, have helped to define these influences and to identify the relative contributions of isolate immunogenicity and host immune response capacity to the outcome of infection. Data from such studies can not only contribute to a better understanding of the biology of this genus but can also throw light on fundamental aspects of host-parasite interactions.

Diel locomotory activity of deer mice (Peromyscus maniculatus) infected with Trichinella nativa or Trichinella pseudospiralis

The effects of infection by two species of sylvatic Trichinella on the diel locomotory activity of a wild rodent host, the deer mouse Peromyscus maniculatus, in a familiar environment were investigated in the laboratory using computer-linked activity chambers equipped with an infrared photocell. Locomotory activity data were collected on each mouse prior to and after sham inoculation or inoculation with graded doses of muscle-encapsulating Trichinella nativa or nonencapsulating Trichinella pseudospiralis larvae. Trichinella nativa infections induced activity deficits in deer mice that were proportional to the number of infective larvae recovered, whereas derived indices of locomotory activity of mice infected with T. pseudospiralis remained essentially within the range of those of sham-inoculated control mice. Quantitative differences between T. nativa and T. pseudospiralis in their potential to modulate the host's immune response may account for the observed difference in their effect on locomotory activity of the deer mouse host. Such variation in trichina-induced changes in diel locomotory activity may serve to channel transmission of the parasites to suitable hosts.

The effect of Trichinella spiralis and Trichinella pseudospiralis on the mechanical properties of mammalian diaphragm muscle

The isometric mechanical properties of diaphragm muscle were studied in mice infected with either Trichinella spiralis or Trichinella pseudospiralis. Measurements of muscle stress were taken at 15, 20, 30 and 40 days post-infection. Infected diaphragm muscle showed a significant (P < 0.001) reduction in muscle stress during both twitch and tetanic contractions when compared with muscle from control animals. T. spiralis caused a significant reduction in resistance to muscle fatigue. The consequences of these changes in muscle function to host pathology are discussed, and related to previous work on the effects of Trichinella on host biochemistry and the immune response.

BIOLOGY OF NEUROCYSTICERCOSIS - PARASITE RELATED FACTORS MODULATING HOST RESPONSE

Neurocysticercosis, caused by infestation of the nervous system by the larval form of Taenia solium, continues to baffle the neurologist, because of varied clinical manifestations. A large body of the literature related to this disease is clinically oriented, enough attention has not been given to parasite related factors modulating the host response. Using immunohistochemical techniques, three features related to the biology of the Cysticercus cellulosa e were studied. Firstly, to the question as to which part of the worm is recognised by the host immune system, the surface glycoprotein is found to be immunolabelled by the CSF from patients of neurocysticercosis. This surface protein is depleted following specific antihelmenthic therapy, thus accounting for a fall in anticysticercal antibosy level in the CSF. Secondly, the cysticercal cyst, by immunochemical and histochemical methods, is found to have "ACTH like" molecule in the body wall and has neurotransmitter and mitochondrial metabolic pathways similar to the host, facilitating the immune evasion and successful parasitisation. Finally, Cysticercus cellulosae is found to contain a "peptide" opening the blood brain barrier at the arteriolar level when injected into mice intravenously. Similar phenomenon may be functional in the patients as well, resulting in cerebral oedema, especially following praziquintel therapy.

Trichinella pseudospiralis overcomes innate resistance of the Chinese hamster to Trichinella spiralis

Infectivity of Trichinella pseudospiralis in Chinese hamsters was greater than that of Trichinella spiralis. Concurrent infection with these two species of parasite was accompanied by an increase in infectivity of T. spiralis. The infectivity of T. pseudospiralis, but not that of T. spiralis, was significantly influenced by host age. Regardless of host age, T. pseudospiralis was more infective for the Chinese hamster than was T. spiralis. Early during infection, enteritis (myeloperoxidase activity) in hamsters infected with T. pseudospiralis alone was significantly less than that seen in animals infected with T. spiralis alone or with both species concurrently. Myositis in hamsters infected with T. pseudospiralis alone was significantly less on days 14, 17 and 25 post-infection (p.i.) than that observed in concurrently infected or T. spiralis-infected animals. On days 11 and 14 p.i. inflammation in diaphragm muscle from concurrently infected hamsters was significantly less than that seen in animals infected with T. spiralis alone. Muscle histology supported these chemical data on myositis. Suppression of the host inflammatory response against early muscle-stage larvae of T. pseudospiralis underlies the greater infectivity of this parasite for the Chinese hamster.