Ribo HRM--detection of inter- and intra-species polymorphisms within ribosomal DNA by high resolution melting analysis supported by application of artificial allelic standards

Ribo HRM, a single-tube PCR and high resolution melting (HRM) assay for detection of polymorphisms in the large subunit ribosomal DNA expansion segment V, was developed on a Trichinella model. Four Trichinella species: T. spiralis (isolates ISS3 and ISS160), T. nativa (isolates ISS10 and ISS70), T. britovi (isolates ISS2 and ISS392) and T. pseudospiralis (isolates ISS13 and ISS1348) were genotyped. Cloned allelic variants of the expansion segment V were used as standards to prepare reference HRM curves characteristic for single sequences and mixtures of several cloned sequences imitating allelic composition detected in Trichinella isolates. Using the primer pair Tsr1 and Trich1bi, it was possible to amplify a fragment of the ESV and detect PCR products obtained from the genomic DNA of pools of larvae belonging to the four investigated species: T. pseudospiralis, T. spiralis, T. britovi and T. nativa, in a single tube Real-Time PCR reaction. Differences in the shape of the HRM curves of Trichinella isolates suggested the presence of differences between examined isolates of T. nativa, T. britovi and T. pseudospiralis species. No differences were observed between T. spiralis isolates. The presence of polymorphisms within the amplified ESV sequence fragment of T. nativa T. britovi and T. pseudospiralis was confirmed by sequencing of the cloned PCR products. Novel sequences were discovered and deposited in GenBank (GenBank IDs: JN971020-JN971027, JN120902.1, JN120903.1, JN120904.1, JN120906.1, JN120905.1). Screening the ESV region of Trichinella for polymorphism is possible using the genotyping assay Ribo HRM at the current state of its development. The Ribo HRM assay could be useful in phylogenetic studies of the Trichinella genus.     

Sylvatic and domestic Trichinella spp. in wild boars; infectivity, muscle larvae distribution, and antibody response

Thirty-six wild boars were inoculated with Trichinella spiralis, Trichinella nativa, Trichinella britovi, Trichinella pseudospiralis (USSR), T. pseudospiralis (USA), T. pseudospiralis (AUST), Trichinella murrelli, Trichinella T6, and Trichinella nelsoni. The wild boars were killed at 5 and 10 wk postinoculation (PI), and the number of muscle larvae per g (lpg) of tissue was determined for 18 muscles or muscle groups. Five weeks PI, all Trichinella genotypes had established as muscle larvae, but their infectivity varied widely: T. spiralis established in high numbers (mean = 296 lpg), T. britovi, T. nelsoni, and 1 of the T. pseudospiralis genotypes (AUST) in moderate numbers (mean = 53-74 lpg), whereas the remaining genotypes were poorly infective (mean 2-16 lpg). Because of considerable weight gain of the wild boars, an estimated total larval burden (live weight x lpg) was calculated for each animal. The total larval burden did not change significantly over time for T. spiralis, T. murrelli, T. britovi, T. nelsoni, and T. pseudospiralis (USA and USSR), whereas a significant reduction could be demonstrated for T. nativa, Trichinella T6, and T. pseudospiralis (AUST). Diaphragm and tongue were predilection sites in wild boars, independent of Trichinella genotype and infection level. At low infection levels, a greater percentage of larvae were found in diaphragm and tongue at 10 wk than 5 wk PI. Antibody responses increased rapidly between weeks 3 and 5 PI. For T. spiralis and T. nelsoni, the high antibody level persisted throughout the experimental period, but for T. nativa, T. britovi, T. murrelli, or Trichinella T6, the levels declined. For T. pseudospiralis, the antibody response increased more gradually between weeks 3 to 10 PI. Infection with all genotypes of Trichinella were detected using any of 7 excretory-secretory antigens, which points to the potential use of 1 common antigen for epidemiological studies on Trichinella in wild boars. In conclusion, T. spiralis is highly infective to wild boars, T. britovi, T. nelsoni, T. pseudospiralis (USA), and T. pseudospiralis (USSR) are moderately infective, and T. nativa, T. murrelli, T. pseudospiralis (AUST), and Trichinella T6 are poorly adapted to this host species.     

Infectivity, persistence, and antibody response to domestic and sylvatic Trichinella spp. in experimentally infected pigs

Groups of pigs were inoculated with genotypes of Trichinella belonging to: Trichinella spiralis, Trichinella nativa, Trichinella britovi, Trichinella pseudospiralis (from Caucasus), T. pseudospiralis (from USA), Trichinella murrelli, Trichinella sp. (from North America), and Trichinella nelsoni. The pigs were sacrificed between 5 and 40weeks p.i., and the number of muscle larvae per gram (l.p.g.) of tissue was determined as an average of 18 muscles. All Trichinella genotypes were infective for pigs, but both their infectivity and persistence varied: 5weeks p.i., T. spiralis muscle larvae were present in high numbers (mean=427l.p.g.), while T. britovi, T. nelsoni, and T. pseudospiralis larvae were present in moderate numbers (means=24-52l.p.g.); larvae of the remaining genotypes were recovered only in low numbers (means=0.05-5. 00l.p.g.). The total larval burden (live weight of pigxl.p.g.) was constant over time for T. spiralis, T. britovi, and T. nelsoni, but declined significantly (P<0.05) for the other genotypes. Antibody responses could be detected 3-4weeks p.i. by seven different Trichinella ES antigens, but the antibody levels and dynamics differed significantly among the experimental groups. In pigs inoculated with T. spiralis, T. britovi, or T. nelsoni, the antibody level increased rapidly between weeks 3 and 5 p.i. and was stable or increased slightly throughout the experimental period. In pigs inoculated with T. nativa, T. murrelli, or Trichinella (T6) (from North America), a rapid increase was detected between weeks 3 and 5 p.i., but for these genotypes a reduction in the antibody levels was seen thereafter. In the pigs inoculated with T. pseudospiralis, the antibody level increased more gradually over a period from week 3 p. i. to weeks 15-20 p.i., and decreased thereafter. In general, all species of Trichinella were detected by any of the seven ES antigens, which points to the potential use of one common antigen for surveillance and epidemiological studies on both domestic and sylvatic Trichinella in pigs. Homologous ES antigens were slightly more sensitive in detecting antibodies to the corresponding Trichinella species.     

Trichinella murrelli n. sp: etiological agent of sylvatic trichinellosis in temperate areas of North America

Trichinella T5, collected from sylvatic carnivores in North America, was identified previously as a different phenotype of Trichinella, with an uncertain taxonomic level due to the availability of only 2 isolates. Cross-breeding experiments carried out with single female and male larvae of 2 strains of Trichinella T5, with single female and male larvae of 2 strains of Trichinella spiralis, Trichinella nativa, Trichinella britovi, Trichinella pseudospiralis, Trichinella nelsoni, and Trichinella T6, showed a reproductive isolation of Trichinella T5. Viable offspring were obtained only when a female of Trichinella T5 was crossed with a male of T. britovi, but not vice versa. Furthermore, the analysis of biological, biochemical, and molecular data of 32 isolates collected from sylvatic animals in the Nearctic region and identified as Trichinella T5 permitted its reassessment at the species level. Trichinella murrelli n. sp. is characterized by the following: distribution in temperate areas of the Nearctic region; newborn larvae production in vitro of 29-36/72 hr; nurse cell development time between 24 and 70 days postinfection; reproductive capacity index in Swiss mice 1.2-9.5, in wild mice 29.5-159.8, in rats 0.7-2.4, and in pigs 0.03-0.0004; no resistance to freezing; ribosomal DNA fragments of 7.2 kb and/or 11.4 kb, plus 2.2 kb and 1.8 kb present after Dra I digested DNA when probed with total T. spiralis RNA; a specific amplicon of 179 bp after polymerase chain reaction (PCR) amplification with the primer set SB147G; a specific fragment of 1,600 bp after PCR amplification with the primer set Ts43CA and Hhb I digestion; long incubation period; and moderate to severe pathogenicity for humans. The new species is most similar to T. britovi, though it differs from T. britovi in the pattern of 2 allozymes, in the patterns of major ribosomal DNA and PCR-restriction fragment length polymorphism fragments, and in geographical distribution.     

Trichinella spp.: differential expression of two genes in the muscle larva of encapsulating and nonencapsulating species.

Kuratli, S., Lindh, J. G., Gottstein, B., Smith, D. F., and Connolly, B. 1999. Trichinella spp.: Differential expression of two genes in the muscle larva of encapsulating and nonencapsulating species. Experimental Parasitology 93, 153-159. The expression of the two genes tsmyd-1 and tsJ5 was studied in the muscle stage larva of three different species of Trichinella. T. spiralis and T. britovi are both encapsulating species, while T. pseudospiralis is a nonencapsulating species. Expression of tsJ5 is developmentally regulated in T. spiralis and has been shown in this study to be down-regulated in the T. pseudospiralis muscle larva compared with the other two species. Immunoblot analysis has also revealed that the relative abundance of the protein product of this gene, TSJ5, is lower in T. pseudospiralis muscle larvae. It has previously been shown that expression of tsmyd-1 is not developmentally regulated in T. spiralis (Connolly et al. 1996). In contrast, expression of this gene is slightly increased in the muscle larvae of T. pseudospiralis. Southern analysis of genomic DNA from the three Trichinella species shows that both genes are highly conserved.     

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.     

Tolerance to low temperatures of domestic and sylvatic Trichinella spp. in rat muscle tissue

The present study was designed to investigate the tolerance to low temperatures of 9 Trichinella isolates in rat muscle tissue. Nine groups of 24 rats were infected with encapsulated Trichinella spiralis, Trichinella nativa, Trichinella britovi, Trichinella murrelli, Trichinella T6, Trichinella nelsoni, and 3 nonencapsulated Trichinella pseudospiralis strains. Six rats from each of the groups were necropsied at 5, 10, 20, and 40 wk postinfection (wpi). Muscle tissues containing Trichinella larvae were exposed to temperatures of -18, -5, and 5 C for 1 or 4 wk, and afterward the reproductive capacity index (RCI) in mice was determined for the 9 individual Trichinella isolates. Only T. nativa muscle larvae were infective after freezing at a temperature of -18 C. At 5 wpi all encapsulated isolates, except for the tropical species T. nelsoni, remained infective after exposure to a temperature of -5 C for both 1 and 4 wk, whereas nonencapsulated T. pseudospiralis survived only 1 wk of exposure. All Trichinella spp. remained infective after exposure to a temperature of 5 C. Muscle larvae for all investigated species remained infective as long as they persisted in live rats during the experiment. Analysis of variance showed a significant effect of age on the temperature tolerance of encapsulated T. spiralis and nonencapsulated T. pseudospiralis. In addition, significant interaction between age of muscle larvae and length of exposure was found. In general Trichinella muscle larvae of medium age (10 and 20 wpi) tolerated freezing better than early and late stages of infection (5 and 40 wpi). This is the first study to demonstrate such a relationship between age of infection and temperature tolerance of Trichinella spp. muscle larvae.     

Allozymic and biological characters of Trichinella pseudospiralis isolates from free-ranging animals.

To evaluate biological and biochemical variability in nonencapsulated Trichinella isolates, biological and allozymic studies were conducted on isolates of Trichinella collected from a raptoral bird (Aquila rapax) and a fox (Vulpes corsac) in Kazakhstan and from a dasyurid marsupial (Dasyurus maculatus) on the island of Tasmania, Australia. Allozyme profiles of bird and marsupial isolates showed close similarity with the type isolate of Trichinella pseudospiralis. The avian and fox isolates successfully interbred with the type T. pseudospiralis isolate, but they failed to interbreed with 3 encapsulating species, Trichinella spiralis, Trichinella nativa, and Trichinella britovi. The reproductive index assessed in 4 inbred and 1 outbred strains of mice was lower for the avian isolate than for the marsupial and the type T. pseudospiralis isolates (P < 0.001).     

Genetic diversity within the genus Trichinella as shown by cleavage fragment length polymorphism analysis

The genetic diversity within the genus Trichinella was studied using cleavage fragment length polymorphism (CFLP) analysis. The CFLP method generates specific fingerprints based on single nucleotide mutations. By this method the amplified intergenic regions of the 5S rRNA genes of the eight different genotypes of Trichinella were analysed. The CFLP pattern of T. spiralis was completely different compared with the sylvatic species T. britovi, T. nativa, T. nelsoni, and the genotypes Trichinella T5, Trichinella T6 and Trichinella T8. The T. pseudospiralis intergenic region can be differentiated by size from the other species of Trichinella.     

Freeze-resistant Trichinella (Trichinella nativa) Established on the Scandinavian Peninsula

Until the 1970’s, Trichinella spiralis (Owen 1835) was considered the only species within the genus Trichinella. Then T. pseudospiralis (Garkavi 1972) was classified as a separate species on the basis of morphological and biological features. The remaining morphologically homogenous “T. spiralis-group” has been split into 4 different species (or subspecies) on the basis of their biological and biochemical characteristics; T. nativa (Britov & Boev 1972), T. nelsoni (Britov & Boev 1972), T. spiralis sensu stricto and T. britovi (Pozio et al. 1992).     

Differentiation between Trichinella spiralis and T. pseudospiralis infective larvae by a monoclonal antibody

Crude saline extracts of Trichinella spiralis and T. pseudospiralis infective larvae were studied by Western blot analysis using a monoclonal antibody, named ES/TA2 and produced against T. spiralis larvae. This monoclonal antibody recognized seven major antigenic components in T. spiralis larvae with apparent Mr: 45, 48, 50, 68, 70, 92 and 105 kDa and five in T. pseudospiralis larvae: 38, 50, 70, 72 and 92 kDa. SDS-PAGE of both extracts did not reveal appreciable differences in the range of molecular weights recognized by ES/TA2. These facts show the existence of immunological differences among proteins with apparently identical molecular weights.     

Infection of the Chinese hamster with Trichinella pseudospiralis

A mean of 2,862 muscle larvae was recovered on day 45 postinfection (PI) from the total body musculature of Chinese hamsters infected with 498 Trichinella pseudospiralis. Infection of the Chinese hamster with 494 Trichinella spiralis resulted in recovery of a mean of 225 muscle larvae on day 45 PI. The reproductive capacity index for T. pseudospiralis was 5.74, whereas that for T. spiralis was 0.46 in this host species.     

Stimulated chemotactic response in neutrophils from Trichinella pseudospiralis-infected mice and the neutrophilotactic potential of Trichinella extracts.

During infection with Trichinella pseudospiralis a strong neutrophil response is evident in the peripheral circulation of the mouse. This study compared the chemotactic response of neutrophils from uninfected, T. pseudospiralis-infected and Trichinella spiralis-infected mice to extracts from adult worms, newborn larvae and muscle-stage larvae of both species of parasite. The chemotactic response of neutrophils from T. pseudospiralis-infected mice to Zymosan-activated mouse serum (ZAMS) was significantly greater than that seen with neutrophils from either uninfected or T. spiralis-infected mice. Unstimulated chemotactic response of neutrophils from these three groups of animals to medium alone was similar. The chemotactic response of neutrophils from the three groups of animals was unaffected by either the concentration or source of serum. The chemotactic response of neutrophils from T. pseudospiralis-infected mice was significantly greater than that observed with cells from uninfected or T. spiralis-infected mice. Among parasite extracts, those from newborn larvae displayed the strongest chemotactic potential for neutrophils. Extracts from muscle larvae of T. spiralis and T. pseudospiralis and extracts of T. spiralis adult worms showed the weakest attraction for neutrophils. Extracts from adult T. pseudospiralis and from newborn larvae of both species elevated the chemotactic response of uninfected mouse neutrophils to a significantly greater level than that seen with ZAMS alone, while a significant reduction in this response was evident only when ZAMS was presented to neutrophils with 500 micrograms of extract from muscle larvae of T. pseudospiralis or T. spiralis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Trichinella papuae n.sp. (Nematoda), a new non-encapsulated species from domestic and sylvatic swine of Papua New Guinea

Encapsulated and non-encapsulated species of the genus Trichinella are widespread in sylvatic animals in almost all zoogeographical regions. In sylvatic animals from Tasmania (Australian region), only the non-encapsulated species Trichinella pseudospiralis has been reported. Between 1988 and 1998, non-encapsulated larvae of Trichinella were detected in five domestic pigs and six wild boars from a remote area of Papua New Guinea. Morphological, biological, and molecular studies carried out on one strain isolated from a wild boar in 1997 suggest that these parasites belong to a new species, which has been named Trichinella papuae n.sp. This species can be identified by the morphology of muscle larvae, which lack a nurse cell in host muscles, and whose total length is one-third greater than that of the other non-encapsulated species, T. pseudospiralis. Adults of T. papuae do not cross with adults of the other species and genotypes. Muscle larvae of T. papuae are unable to infect birds, whereas those of T. pseudospiralis do. The expansion segment V of the large subunit of the ribosomal DNA differs from that of the other species and genotypes. All of these features allow for the easy identification of T. papuae, even in poorly equipped laboratories. The discovery and identification of a second non-encapsulated species in the Australian region strongly supports the existence of two evolutionary lines in the genus Trichinella, which differ in terms of the capacity of larvae to induce a modification of the muscle cell into a nurse cell.     

Differences and similarities of nurse cells in cysts of Trichinella spiralis and T. pseudospiralis

The nurse cell in the cyst of Trichinella spiralis comprises at least two kinds of cytoplasm, derived from muscle or satellite cells, as indicated by the pattern of staining using regular dye (haematoxylin and eosin, or toluidine blue), alkaline phosphatase (ALP) expression, acid phosphatase (ACP) expression and immunostaining with an anti-intermediate filament protein (desmin or keratin). Muscle cells undergo basophilic changes following a T. spiralis infection and transform to the nurse cells, accompanied by an increase in ACP activity and the disappearance of desmin. Satellite cells are activated, transformed and joined to the nurse cells but remain eosinophilic. The eosinophilic cytoplasm is accompanied by an increase in desmin and ALP expression but not an increase in ACP activity. Differences in the staining results for ALP or ACP suggest that the two kinds of cytoplasm have different functions. Trichinella pseudospiralis infection results in an increase of ACP activity at a later stage than T. spiralis. There is also a difference in the location pattern of ACP in the cyst of T. spiralis compared with T. pseudospiralis. In T. spiralis, ACP is diffused within the cell, but in T. pseudospiralis, ACP distribution is spotty corresponding to the location of the nucleus. Trichinella pseudospiralis infection is accompanied by a slight increase in ALP activity. Activated satellite cells following a T. pseudospiralis infection exhibit an increase in desmin expression. The present study therefore reveals that nurse cell cytoplasm differs between the two Trichinella species and between the two origins of cytoplasm in the cyst of T. spiralis.     

Trichinella britovi etiological agent of sylvatic trichinellosis in the Republic of Guinea (West Africa) and a re-evaluation of geographical distribution for encapsulated species in Africa

In West Africa, Trichinella infection was documented in humans and animals from Senegal in the 1960s, and the biological characters of one isolate showed a lower infectivity to domestic pigs and rodents when compared with that of a Trichinella spiralis pig isolate from Europe. To identify the Trichinella species present in West Africa, a survey was conducted in a total of 160 wild animals in the Republic of Guinea. Three Viverridae, one true civet (Viverra civetta) and two African palm civets (Nandinia binotata) from the Fouta Djallon Massif, Pilimini Subprefecture, were found positive by artificial digestion of muscle samples. Trichinella larvae from these three viverrids were identified as Trichinella britovi and no difference was detected in three examined sequences from these African isolates and the reference strain of T. britovi from Europe, indicating common ancestry, an historically continuous geographic distribution, and recent isolation for African and European populations. The detection of T. britovi in West Africa modifies our knowledge about the distribution of encapsulated species of Trichinella in Africa. Thus, Trichinella nelsoni is now considered to have a distribution limited to the Eastern part of the Afrotropical region from Kenya to South Africa. This provides a plausible explanation for the presence of Trichinella T8 in Namibia and South Africa, and further suggests that T. britovi could be the Trichinella species circulating among wild animals of Northern Africa.     

Taxonomic revision of the genus Trichinella.

The analysis of genetic, biochemical, and biological data on about 300 Trichinella isolates, reported in the literature, allows a taxonomic revision of this genus. We propose the recognition of 5 sibling species, Trichinella spiralis (Owen, 1835) sensu stricto; Trichinella nativa Britov and Boev, 1972; Trichinella pseudospiralis Garkavi, 1972; Trichinella nelsoni Britov and Boev, 1972 sensu stricto; and Trichinella britovi n. sp., on the basis of biochemical and biological characteristics. Trichinella britovi n. sp. is characterized by distribution in the Palaearctic Region; newborn larvae (NBL) production in vitro of 35-55 NBL/72 hr; nurse cell development time (NC d.t.) between 24 and 42 days postinfection (d.p.i.); low reproductive capacity index (RCI) in mice, rats, and pigs; low resistance to freezing; 1 unique marker allozyme; and moderate pathogenicity for humans. The new species is most similar to Trichinella nativa but differs from it in 4 allozymes, in having less resistance to freezing, in having a different pattern of major ribosomal DNA fragments after endonuclease digestion, and in distribution area. Trichinella nativa is characterized by a holarctic distribution; hosts that are sylvatic mammals; NBL production in vitro 28-54/72 hr; NC d.t. between 20 and 30 d.p.i.; low RCI in mice, rats, and pigs; high resistance to freezing; 2 unique marker allozymes; and moderate to severe pathogenicity for humans. Trichinella spiralis sensu stricto is characterized by a cosmopolitan distribution in domestic pigs, associated wildlife, and humans; high NBL production in vitro (greater than 90 NBL/72 hr); NC d.t. between 16 and 37 d.p.i.; high RCI in mice, rats, and pigs; no resistance to freezing; 6 unique marker allozymes; and high pathogenicity for humans.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sylvatic trichinellosis in southwestern Spain

The epidemiology of Trichinella spp. in their main sylvatic hosts, wild boar (Sus scrofa ferus and red fox (Vulpes vulpes), in Extremadura (southwestern Spain) was studied. We examined 88 Trichinella spp.-positive wild boar muscle-tissue samples from a total of 29,333 killed animals, referred to the Veterinary Parasitology Department (University of Extremadura, Spain) by the Extremadura Veterinary Service. Additionally, 227 red foxes killed during the hunting season and thus not subject to veterinary controls were examined for trichinellosis. Trichinella spp. larvae were found in six (3%) of the red foxes. All samples were examined using direct diagnostic techniques, including trichinoscopy and artificial digestion. The mean intensity of infection was 74.8 larvae/g (LPG) of muscle tissue in wild boars, compared to 30.6 LPG in foxes. Trichinella spiralis (sensu stricto) predominated over T. britovi in wild boars. Random amplified polymorphic DNA (RAPD) and alloenzyme typing showed that 74% of infected wild boars had only T. spiralis, 21% had only T. britovi, and 5% showed mixed infections. In contrast, 33% of infected foxes were infected only with T. spiralis, while 67% had T. britovi, suggesting a clear predominance of the latter in foxes. We suspect the existence of a paranthropic or sylvatic cycle in large areas of this region; given the ease of transfer between sylvatic and domestic or semi-domestic animals, this implies a high epidemiological risk.     

Biological and immunological characteristics of Trichinella pseudospiralis

In 1972 three new species were proposed for the genus Trichinella, which for 137 years had contained a single species, Trichinella spiralis (Owen,1835). One of these proposed species, Trichinella pseudospiralis, was markedly different from the others in that it was smaller in size, the muscle-stage larvae were not surrounded by a capsule, and it was capable of parasitizing birds. Owing to a lack of information on the normal host range, geographic distribution, biochemistry, immunology and normal variation in biological characteristics of these organisms, several authors supported the more conservative position of designating them sibling species, subspecies or races of Trichinella. The summary statement following the session on Parasite Genetics and Speciation at the 7th International Conference on Trichinellosis recommended that pseudospiralis be accepted as a new species of Trichinella. In this article George Stewart reviews the available information on the biological and immunological characteristics of T. pseudospiralis.