A preliminary investigation on the infectivity of Trichinella larvae in traditional preparations of walrus meat

This study evaluated the infectivity of Trichinella nativa in freshly frozen walrus meat and traditionally aged walrus meat (igunaq) associated with two human outbreaks of trichinellosis in the Canadian Arctic. Trichinella larvae recovered from walrus meat stored at -20 degrees C for up to 20 months remained infective for guinea pigs inoculated with 135 or 716 larval doses. However, none of the 4-5 and 10-month-old igunaq preparations contained infective T. nativa larvae as measured by bioassays using mice and guinea pigs at inoculation doses ranging from 6 to 500 larvae. This indicates that the degradation process that occurred in the field can be sufficient to either kill Trichinella larvae or render them non-infective for mice and guinea pigs. Further research is needed to evaluate the food safety risk of traditional walrus igunaq aged under different field conditions and storage times.

[Trichinellosis outbreaks in Spain (1990-2001)]

INTRODUCTION

Trichinellosis is a helminth infection having a wide geographical distribution. It is acquired by ingestion of raw or undercooked meat infected with Trichinella spp. The present work reviews the human trichinellosis outbreaks recorded in Spain during 1990-2001, taking into account both the geographical distribution and source of the infection.

METHODS

The parasite was isolated from suspected meats with the digestion technique. Molecular characterization of Trichinella isolates was done by random amplified polymorphic DNA (RAPD) analysis and Western-blot with US5 and US9 monoclonal antibodies. Anti-Trichinella antibodies in the patients' sera were investigated by indirect immunofluorescence (IIF).

RESULTS

A total of 49 trichinellosis outbreaks were detected in Spain during 1990-2001, 75.5% produced by ingestion of infected wild boar, 14.3% by infected domestic pig and 10.2% by an unknown source. Of the 49 outbreaks, 21 were followed up in our laboratory. We were able to perform molecular identification of the Trichinella species involved in 13 outbreaks, with 61.5% produced by T. britovi and 38.5% by T. spiralis. Serological diagnosis of the trichinellosis patients by IIF allowed confirmation of helminth infection.

CONCLUSIONS

With the use of molecular markers, T. spiralis and T. britovi were identified as the causative organisms in trichinellosis outbreaks detected in Spain during 1990-2001. These results reveal the importance of T. britovi in Spanish public health.

[A concept of parasite species at the times of molecular studies]

The problem of species recognition in relation to parasite organisms is discussed, based on literature data. Taking into account that over 20 species concepts have hitherto been formulated, the choice of characters, which should define a species differs from author to author. Lately the differences in some gene fragments are regarded as one of most important feature for species differentiation. On this basis some lineages, genotypes or strains have been differentiated within some species, but in most cases the respective authors did not decide to elevate these units to the species level. The present paper focuses on the studies on species representing three genera (Taenia, Echinococcus, Trichinella) as they show, especially the complex studies on the species within the genus Trichinella, how big material is necessary to formulate any proper conclusion and, on the other hand, that the differences in the DNA sequences cannot be the only characters defining species; some other features (morphological, biological, behavioral) should not be considered redundant.

Heterogeneity and immunogenicity of the Trichinella TSL-1 antigen gp53

This study investigates the heterogeneity and immunogenicity of the Trichinella TSL-1 antigen gp53. Western blotting analysis of several Trichinella isolates with the gp53-specific monoclonal antibodies (mAbs) US5 and US9, produced in Btkxid mice, revealed that gp53 from the species T. britovi, T. murrelli and genotype T8 had higher MW (60 kDa) than gp53 from T. spiralis, T. nelsoni and genotype T6 (53 kDa) and from T. nativa (55 kDa). mAb US5 reacted only with gp53 from T. spiralis. Experiments including immunoassays of gp53 binding by sera from T. spiralis-infected mice, in the presence of different potential inhibitors (recombinant gp53, US5, T. britovi-crude larval extract (CLE), and CLE N- and O-glycans), indicate (i) that gp53 from T. spiralis bears specific epitopes that induce antibody formation during infection; (ii) that the protein epitopes of gp53 are much more important (76 or 68% of total antibody reactivity in BALB/c and Swiss CD-1 mice, respectively) than the corresponding glycan epitopes including tyvelose (11 or 32% of total reactivity) for the induction of anti-gp53 circulating antibodies; and (iii) that the species-specific epitopes present on gp53 are differentially recognized in different mouse strains. Whereas in BALB/c mice US5- and non-US5-recognized species-specific epitopes on gp53 bind about 84% of circulating antibodies on day 80 post-infection, this percentage was only 38% in Swiss CD-1 mice. These data on the antigenicity of gp53 contrast with data for Trichinella CLE antigens, in that most circulating antibodies reactive with CLE antigens recognized tyvelose-containing epitopes (57% and 58% of circulating antibodies in BALB/c and Swiss CD-1 mice, respectively). Together these results demonstrate that gp53 is recognized during infection but is antigenically different from other Trichinella TSL-1 antigens.

Biochemical analysis of encapsulated and non-encapsulated species of Trichinella (Nematoda, Trichinellidae) from cold- and warm-blooded animals reveals a high genetic divergence in the genus

Multilocus enzyme electrophoresis was used to analyse genetic variation in the genus Trichinella. Twenty-eight isolates belonging to eight species and six genotypes were analysed for 12 enzyme systems, producing 19 different phenotypes. According to Jaccard's similarity index, the isolates clustered into two main groups, specifically, encapsulated species/genotypes and non-encapsulated species/genotypes. Furthermore, the non-encapsulated species clustered into two other groups: the species infecting mammals and birds ( Trichinella pseudospiralis) and those infecting mammals and reptiles ( Trichinella papuaeand Trichinella zimbabwensis). The encapsulated species/genotypes, which only infect mammals, clustered into four main groups: the cosmopolitan species Trichinella spiralis, the species/genotypes of the temperate regions ( Trichinella britovi, Trichinella murrelli, Trichinella T8, and Trichinella T9), the species/genotype of the arctic region ( Trichinella nativa and Trichinella T6), and the equatorial species Trichinella nelsoni. These results are consistent with biological, epidemiological, and molecular data, which show a high genetic divergence in this genus.

Biological variation in Trichinella species and genotypes

At present, the genus Trichinella comprises seven species of which five have encapsulated muscle larvae (T. spiralis, T. nativa, T. britovi, T. nelsoni and T. murrelli) and two do not (T. pseudospiralis and T. papuae) plus three genotypes of non-specific status (T6, T8 and T9). The diagnostic characteristics of these species are based on biological, biochemical and genetic criteria. Of biological significance is variation observed among species and isolates in parameters such as infectivity and immunogenicity. Infectivity of Trichinella species or isolates is determined, among other considerations, by the immune status of the host in response to species- or isolate-specific antigens. Common and particular antigens determine the extent of protective responses against homologous or heterologous challenge. The kinetics of isotype, cytokine and inflammatory responses against T. spiralis infections are isolate-dependent. Trichinella spiralis and T. pseudospiralis induce different dose-dependent T-cell polarizations in the early host response, with T. spiralis initially preferentially promoting Th1-type responses before switching to Th2 and T. pseudospiralis driving Th2-type responses from the outset.

Molecular expression and characterization of a homologue of host cytokine macrophage migration inhibitory factor from Trichinella spp

A homologue of cytokine macrophage migration inhibitory factor (MIF) from complementary DNA (cDNA) of Trichinella spiralis and Trichinella pseudospiralis was expressed in Escherichia coli and characterized. The sequence analysis indicated that the predicted amino acid sequence has an identity of 57 and 44% with the MIF of nematodes Trichuris trichiura and Brugia malayi respectively, and 41 and 40% with that of a human and a mouse, respectively. The identity in sequences of cDNA and amino acids between T. spiralis and T. pseudospiralis was 91 and 86%, respectively. Western blot analysis showed that anti-MIF antibodies positively stained proteins from the extracts of adult worms or muscle larvae migrating at about 12.5 kDa (3 isoforms with isoelectric point 5.23, 5.72, and 6.29). Semiquantitative reverse transcriptase-polymerase chain reaction revealed that the gene was expressed in various developmental stages, including in adult worms, newborn larvae, precyst muscle larvae, and postcyst muscle larvae, although there was difference in the expression level among these stages. The immunohistochemical analysis showed the MIF exists in the muscle cells of the body wall and some stichocytes of larvae. Histopathology of T. spiralis-infected muscles revealed an accumulation of mononuclear cells around the worms, and immunocytochemical staining showed these cells were not macrophages. Mononuclear cells, including macrophages, were, however, observed in cardiac muscles where the parasite did not encyst. Macrophages accumulated around the Sephadex beads transplanted in mice subcutaneously, but this accumulation was profoundly inhibited when the beads were pretreated with MIF recombinant protein.

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.

Molecular identification of natural hybrids between Trichinella nativa and Trichinella T6 provides evidence of gene flow and ongoing genetic divergence

To date, there are no data available on the population genetics of Trichinella due to the lack of genetic markers and the difficulty of working with such small parasites. In the Arctic region of North America and along the Rocky Mountains, there exist two genotypes of Trichinella, Trichinella nativa and Trichinella T6, respectively, which are well differentiated by biochemical and molecular characters. However, both are resistant to freezing, show other common biological characters (e.g. low or no infectivity to rodents and swine) and produce fertile F1 offspring upon interbreeding. To data, these two genotypes have been considered allopatric. In this study, we detected both genotypes in wolves of the same wolf packs in Alaska, suggesting sympatry. A single GTT trinucleotide present in the ITS-2 sequence of T. nativa but not in Trichinella T6 was used as a genetic marker to study gene flow for this character in both a murine infection model and in larvae from naturally-infected Alaskan wolves. Only F1 larvae originating from a cross between T. nativa male and Trichinella T6 female were able to produce F2 offspring. Larvae (F1) originating from a cross between Trichinella T6 male and T. nativa female were not reproductively viable. As expected, all F1 larvae showed a heterozygote pattern for the GTT character upon heteroduplex analysis; however, within the F2 population, the number of observed heterozygotes (n=52) was substantially higher than expected (n=39.08), as supported by the F(is) index, and was not in the Hardy-Weinberg equilibrium. Larvae from two of the 16 Trichinella positive Alaskan wolves, showed the Trichinella T6 pattern or the T. nativa/Trichinella T6 hybrid pattern. Our data demonstrate that T. nativa and Trichinella T6 live in sympatry at least in Alaskan wolves, where T. nativa occurs more frequently (69%) than Trichinella T6 (31%). One explanation for this phenomenon is that glacial periods may have caused a geographical relocation, colonisation and independent evolution of T. nativa within the Rocky Mountains, resulting in a bifurcation of the freeze-resistant genotype. Additional studies will be required to test this hypothesis.

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.

Trichinellosis in China: epidemiology and control

The first outbreak of human trichinellosis in China, according to official national publication, was registered in Tibet in 1964. Since then, more than 500 outbreaks, numbering 25161 cases with 240 deaths, have been recorded. However, this reported quantity is probably highly underestimated because adequate diagnostic techniques might not have been available in the whole area. Moreover, infection in animals is widespread over China, with the prevalence of pig trichinellosis being as high as 4% in some provinces. The estimated situation of trichinellosis in China highlights the necessity not only for its control, but also for the government to elaborate new regulations and guidelines for animal inspection.

Taxonomy of Trichinella and the epidemiology of infection in the Southeast Asia and Australian regions

Seven species belonging to the Trichinella genus (five with encapsulated larvae and two with non-encapsulated larvae in host muscles) and three additional genotypes have been described to date: T. spiralis (genotype T1), a cosmopolitan species with a high infectivity to swine and rats; T. nativa (T2), etiological agent of sylvatic trichinellosis in arctic and subarctic areas of the Holarctic region, and its related genotype (Trichinella T6), detected in Alaska, Idaho, Montana, Pennsylvania, Wyoming, and Ontario; T. britovi (T3), etiological agent of sylvatic trichinellosis in temperate areas of Europe and Asia, and its related genotypes Trichinella T9 in Japan and Trichinella T8 in South Africa and Namibia; T. murrelli (T5), etiological agent of sylvatic trichinellosis in temperate areas of the USA; T. nelsoni (T7), etiological agent of sylvatic trichinellosis in Africa south of the Sahara; T. pseudospiralis (T4), a non-encapsulated cosmopolitan species infecting both mammals and birds; and T. papuae (T10), a recently discovered non-encapsulated species in sylvatic swine of Papua New Guinea. In the Southeast Asia and Australian regions, T. spiralis, T. pseudospiralis and T. papuae have been detected in sylvatic and domestic animals and in humans. A focus of human trichinellosis due to T. papuae was recently discovered in Papua New Guinea, with a prevalence of 28.9%. Trichinellosis has also been documented in domestic animals and/or humans in Cambodia, Indonesia (Bali and Sumatra), Lao PDR, Malaysia, Myanmar, Thailand, and New Zealand, and in wildlife of Tasmania.

Expression of excretory and secretory protein genes of Trichinella at muscle stage differs before and after cyst formation

By adapting a semi-quantitative reverse transcriptase-PCR (RT-PCR) method, we investigated kinetics of gene expression at different developmental stages of Trichinella spiralis and T. pseudospiralis. The analyzed genes included four kinds of excretory and secretory (ES) proteins, a heat shock protein (HSP) and a DNA binding protein and showed that T. spiralis and T. pseudospiralis expressed ES proteins in a stage-specific manner. The gene encoding a 43 kDa ES protein was expressed by muscle larvae, either pre-cyst or post-cyst larvae. The genes encoding: the 53 kDa ES protein of T. spiralis; 53 kDa ES protein of T. pseudospiralis; and 19.6 kDa ES protein of T. spiralis were expressed by post-cyst larvae and adult worms, but not expressed by pre-cyst larvae or newborn larvae. The results showed that pre-cyst larvae and post-cyst larvae are similar but different in the expression of 53 and 19.6 kDa ES proteins. On the other hand, genes of housekeeping proteins, such as HSP and the DNA binding protein, were expressed at all stages although there were some differences in the expression level.

Molecular cloning and characterization of a novel protein of Trichinella pseudospiralis excretory-secretory products

A novel excretory-secretory (ES) protein of Trichinella pseudospiralis was produced. A cDNA library was constructed from mRNA of muscle larvae at 30 days post infection (p.i.) and immunoscreened with the antibody against ES products. A clone, designated Tp22-3, contained a cDNA transcript of 815 bp in length with a single open reading frame which encoded 244-amino acids (28407 Da in the estimated molecular mass). A database search revealed that no sequences had a homology to this predicted protein. The recombinant protein was produced in an Escherichia coli expression system. Stage specific expression of this protein was suggested from the following experiments. An antibody against the recombinant protein could stain proteins migrating at about 28 kDa (which is the expected size from the sequence) on Western blotting of crude extracts or ES products from 30 days p.i. muscle larvae, but failed to stain any proteins in crude extracts from newborn larvae or 15 days p.i. muscle larvae. The antibody reacted to the stichocytes of larvae at 30 days p.i., but did not react to 15 days p.i. muscle larvae. The production of an mRNA transcript for Tp22-3 gene was restricted largely to the 30 days p.i. muscle larvae and adult worms.

Associations between Trichinella species and host species in Finland

Examination of 627 wild animals--raccoon dogs (Nyctereutes procyonoides), red foxes (Vulpes vulpes), European lynxes (Lynx lynx), brown bears (Ursus arctos), wolves (Canis lupus), and badgers (Meles meles)--revealed Trichinella spp. The prevalence varied according to geographical region of Finland (north; southwest, SW; and southeast, SE) and was the highest among lynxes (70%, SW). The risk of trichinellosis was higher in the SE (odds ratio, OR, 19.4) and SW regions (OR 14.3), as compared with the northern region (OR 1), with no difference between the former 2 regions. Foxes (OR 2.1) and lynxes (OR 1.9) had a higher risk than raccoon dogs (OR 1) of being infected. The distribution of different Trichinella species was evaluated in 87 wild and domestic mammals by multiplex polymerase chain reaction. Trichinella spiralis was detected more often in domestic and synanthropic animals than in sylvatic hosts. Trichinella nativa was detected only in wildlife. Trichinella pseudospiralis was found both in sylvatic and synanthropic hosts. Trichinella britovi was detected only in mixed infections with other Trichinella species. The raccoon dog was the sole host for all 4 Trichinella species and also carried the most intense infections.

Trichinella infection in wildlife of the southwestern United States

Several potential mammalian reservoirs of sylvatic species of Trichinella were examined from Texas, New Mexico, and Arizona. During 1998-99, tongues were collected from a black bear (Ursus americanus) in Arizona; from 9 black bears, a coyote (Canis latrans), and a mountain lion (Felis concolor) in New Mexico; and from 154 coyotes, 32 raccoons (Procyon lotor), 13 opossums (Didelphis marsupialis), 4 ocelots (Leopardus pardalis), 3 bobcats (Lynx rufus), and 5 feral hogs (Sus scrofa) in southern Texas. Larvae of Trichinella murrelli were identified by a multiple-polymerase chain reaction analysis in 1 black bear (11.1%) from New Mexico and in 7 coyotes (4.5%) of Texas, whereas Trichinella spiralis larvae were detected in the black bear of Arizona. This is the first report of Trichinella infection in wildlife of New Mexico and Texas and extends the distribution of T. murrelli into the southwestern United States near the border of Mexico.

Infectivity, persistence and serological response of nine Trichinella genotypes in rats

Domestic and sylvatic Trichinella genotypes were evaluated for infectivity, muscle larvae persistence, and host antibody responses in rats. Groups of rats were inoculated with T. spiralis, T. nativa, T. britovi, three genotypes of T. pseudospiralis (from USSR, USA, and Australia), T. murrelli, Trichinella T6, and T. nelsoni, respectively. The muscle larvae intensity (larvae per gram), total larval burden (lpg x rat weight), and the antibody levels were determined at necropsy 5, 10, 20, and 40 weeks post inoculation. All Trichinella genotypes were established in the rats, but infectivity and persistence differed significantly: T. spiralis established and persisted in high numbers, the three T. pseudospiralis genotypes were also highly infective but differed significantly in persistence, T. britovi and T. nativa had limited infectivity and persistence, Trichinella T6 had low infectivity and very low persistence, and T. murrelli and T. nelsoni were almost non-infective. Except for T. spiralis, initial total muscle larval burdens declined significantly for other genotypes during the experiment. A high initial serological response was detected for all genotypes, but the antibody levels decreased rapidly in relation to decreasing larval burdens. After 20 w.p.i. the antibody levels remained high only in T. spiralis and T. pseudospiralis infected rats. The high infectivity and persistence of T. pseudospiralis in rats, suggests that in addition to T. spiralis, this species might be of significant importance in the domestic cycle of trichinellosis.

Trichinellosis in farmed wild boar: meat inspection findings and seroprevalence

A reflection of highly prevalent endemic wildlife trichinellosis is seen in wild boar farming in Finland. During the last five years, 0.7% (15/2265) of wild boars undergoing official meat inspection have been determined to be Trichinella-positive. These findings originate from six different farms. In Finland, T. spiralis and T. pseudospiralis have been discovered in meat inspection of wild boars. ELISA showed 11 out of 99 serum samples (11%) as having specific antibodies for T. spiralis crude antigen. Positive samples were from three out of the thirteen farms from which the sera were available. Most of the positive serum samples (8/11) originated from a farm where trichinellosis was also revealed in meat inspection, the other two seropositive farms were without previous Trichinella records. Over the last few decades, no reports have been made of human trichinellosis acquired in Finland. This indicates both efficient meat inspection as well as public awareness of high-risk foodstuff.

Twelve years of activity of the International Trichinella Reference Centre

The ITRC is the official reference laboratory of both the International Commission on Trichinellosis (since 1988) and the International Office of Epizootics (since 1992). The ITRC was created as a repository for Trichinella strains and as a source of materials and information for international research in 1988. To date, about 900 isolates of human and animal origin from throughout the world have been examined and identified by new procedures developed at the ITRC or in collaboration with other institutions. Using material from this collection, the ITRC has provided a complete revision of the systematics of the genus Trichinella. The ITRC database can be consulted by accessing the web-site: www.simi.iss.it/trichinella/index.htm.

Biological and genetic characteristics of two Trichinella isolates in China; comparison with European species

The most recent taxonomic revision in Trichinella genus included 10 taxa. Trichinella spiralis (Ts) is a thoroughly studied species but most of the isolates came from the Europe or American continents. Few information is available from China about the Trichinella isolates and their diversity. In this report two Chinese isolates were characterized and compared with European strains. The in vitro release of newborn larvae (NBL) was determined for the two species. NBL is observed in supernatant of cell culture after adults purification on day 4 post infection (pi) with Ts, and on day 5 pi with Trichinella nativa (Tna). A new parameter was thus proposed to characterize Trichinella strains. Restriction fragment length polymorphism (RFLP) of genomic DNA and random amplified polymorphic cDNA (RAPD) were used to define genetic variability among different isolates. Species specific pattern could be obtained with RAPD but it was far more difficult to get geographical markers for Trichinella using these methods. A low genetic variability in Trichinella species (i.e. a strong "clonality") is suggested.

A single, multiplex PCR for differentiating all species of Trichinella

The genus Trichinella is currently divided into seven species and at least three additional, unclassified genotypes, Trichinella T6, T8 and T9, where both T8 and T9 have been deemed very similar to T. britovi. Other than for the non-encapsulated species, the absence of distinguishing morphological characters and the overlapping nature of the biological characters within this genus make these traits unsuitable for diagnosis. Consequently, we have developed a simple PCR test for the unequivocal differentiation of all currently recognized species of Trichinella including Trichinella T6. DNA sequence data from each Trichinella genotype were generated from internal transcribed spacers, ITS1 and ITS2, and from expansion segment V (ESV) of the rDNA repeat, from which five different PCR primer sets were chosen. When used simultaneously, this primer mix generates a simple and unique electrophoretic DNA banding pattern for each species and genotype. The ESV-derived primer set contributes at least one band to each agarose gel-derived genotypic pattern and therefore functions as an internal control for PCR integrity. Geographical isolates of each Trichinella genotype were used to verify the reliability and reproducibility of respective DNA banding patterns using single muscle larvae.

The detection of encapsulated and non-encapsulated species of Trichinella suggests the existence of two evolutive lines in the genus

In recent years, the discovery of many non-encapsulated isolates of Trichinella, designated Trichinella pseudospiralis and the identification of a new non-encapsulated species, Trichinella papuae, has revealed that the biomass of the genus Trichinella does not only include the well known encapsulated species (T. spiralis, T. nativa, T. britovi, T. murrelli, and T. nelsoni) but also includes geographically disseminated, non-encapsulated species that represent important biological entities in the genus. Larvae of the first stage (L1) of both non-encapsulated and encapsulated species are able to penetrate the muscle cell and induce a dedifferentiation of this cell. But following this point in the parenteral cycle, non-encapsulated and encapsulated species diverge with respect to their developmental strategies where L1 of encapsulated species are able to induce the nurse cell to synthesize collagen, unlike non-encapsulated larvae which do not induce collagen production. The presence or absence of a collagen capsule is of great importance in the natural cycle of these parasites in that it allows the encapsulated larva to survive to substantially longer periods of time and therefore remain infective even within putrified muscle tissue.

Evaluation of two PCR-based techniques for molecular epidemiology in Finland, a high-endemic area with four sympatric Trichinella species

Trichinella larvae collected from wildlife, domestic and synanthropic animals in Finland were identified to species by two molecular techniques: Random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) and the recently described multiplex PCR. The RAPD-PCR was very sensitive to the sub-optimal preservation muscle larvae and resulting in weak and smeared bands on the gels for such material. However, the same samples yielded easily recognizable bands in the multiplex PCR; this latter technique is then recommended for epidemiological studies, especially when the preservation of the samples is sub-optimal. For larvae in good condition the unequivocal bands obtained by multiplex was the easiest identifiable. Four species of Trichinella were identified in the material: T. spiralis, T. nativa, T. britovi, and T. pseudospiralis. Trichinella britovi is a new record for Finland, and T. pseudospiralis is a new record for Northern Europe. Mixed infections between T. britovi and T. spiralis, T. nativa and T. spiralis, and between T. britovi and T. nativa were detected; this is the first record of a mixed infection between T. spiralis and T. nativa in a naturally infected host. Raccoon dogs were the only host species from which all of the four Trichinella species were detected. Trichinella spiralis was found in both domestic animals and wildlife, but none of the sylvatic Trichinella species were detected in domestic pig.

The lateral flow card test: an alternative method for the detection of Trichinella infection in swine

A novel lateral flow card (TS-Card pork) test was developed for the serological detection of Trichinella infected pigs. Based on extensive studies performed in Romania during 1999-2000 this test proved to be highly specific sensitive, rapid (3-12 minutes) and easy to use (no need for laboratory facilities). It can be used both for the detection of Trichinella infection in carcasses and for epizooliological studies using a variety of samples including whole or dried blood, serum, or tissue fluids. The TS-Card pork test, used as a screening test, can be the foundation of an on-farm or field based inspection system to significantly improve food safety in countries with a high prevalence of Trichinella in pigs or other food animal species. The results presented are also promising for application of the test in an on-line laboratory based inspection system since the speed of the test allows sufficient time to rail out suspected hog carcasses during the slaughter process.