A cladistic analysis of the Trichostrongyloidea (Nematoda)

Epidemiology and diversity of gastrointestinal tract helminths of wild ruminants in sub-Saharan Africa: a review

This review summarises studies on distribution, diversity, and prevalence of gastrointestinal helminth infections in wild ruminants in sub-Saharan Africa. The results showed that 109 gastrointestinal tract (GIT) helminth species or species complexes were recorded in 10 sub-Saharan African countries. South Africa reported the highest number of species because most studies were carried out in this country. Eighty-eight nematode species or species complexes were recorded from 30 wild ruminant species across eight countries. The genus Trichostrongylus recorded the highest number of species and utilised the highest number of wild ruminant species, and along with Haemonchus spp., was the most widely distributed geographically. Fifteen trematode species or species complexes were reported from seven countries. The genus Paramphistomum recorded the highest number of species, and Calicophoron calicophoron was the most commonly occurring species in sub-Saharan African countries and infected the highest number of hosts. Six cestode species or species complexes from one family were documented from 14 wild hosts in seven countries. Moniezia spp. were the most commonly distributed in terms of host range and geographically. Impala were infected by the highest number of nematodes, whilst Nyala were infected by the highest number of trematode species. Greater kudu and Impala harbored the largest number of cestodes. The prevalence amongst the three GIT helminths taxa ranged between 1.4% and 100% for nematodes, 0.8% and 100% for trematodes, and 1.4% and 50% for cestodes. There is still limited information on the distribution and diversity of GIT helminths in wild ruminants in most sub-Saharan African countries.

The identification of small molecule inhibitors with anthelmintic activities that target conserved proteins among ruminant gastrointestinal nematodes

Gastrointestinal nematode (GIN) infections are a major concern for the ruminant industry worldwide and result in significant production losses. Naturally occurring polyparasitism and increasing drug resistance that potentiate disease outcomes are observed among the most prevalent GINs of veterinary importance. Within the five major taxonomic clades, clade Va represents a group of GINs that predominantly affect the abomasum or small intestine of ruminants. However, the development of effective broad-spectrum anthelmintics against ruminant clade Va GINs has been challenged by a lack of comprehensive druggable genome resources. Here, we first assembled draft genomes for three clade Va species (Cooperia oncophora, Trichostrongylus colubriformis, and Ostertagia ostertagi) and compared them with closely related ruminant GINs. Genome-wide phylogenetic reconstruction showed a relationship among ruminant GINs structured by taxonomic classification. Orthogroup (OG) inference and functional enrichment analyses identified 220 clade Va-specific and Va-conserved OGs, enriched for functions related to cell cycle and cellular senescence. Further transcriptomic analysis identified 61 taxonomically and functionally conserved clade Va OGs that may function as drug targets for new broad-spectrum anthelmintics. Chemogenomic screening identified 11 compounds targeting homologs of these OGs, thus having potential anthelmintic activity. In in vitro phenotypic assays, three kinase inhibitors (digitoxigenin, K-252a, and staurosporine) exhibited broad-spectrum anthelmintic activities against clade Va GINs by obstructing the motility of exsheathed L3 (xL3) or molting of xL3 to L4. These results demonstrate valuable applications of the new ruminant GIN genomes in gaining better insights into their life cycles and offer a contemporary approach to discovering the next generation of anthelmintics.IMPORTANCEGastrointestinal nematode (GIN) infections in ruminants are caused by parasites that inhibit normal function in the digestive tract of cattle, sheep, and goats, thereby causing morbidity and mortality. Coinfection and increasing drug resistance to current therapeutic agents will continue to worsen disease outcomes and impose significant production losses on domestic livestock producers worldwide. In combination with ongoing therapeutic efforts, advancing the discovery of new drugs with novel modes of action is critical for better controlling GIN infections. The significance of this study is in assembling and characterizing new GIN genomes of Cooperia oncophora, Ostertagia ostertagi, and Trichostrongylus colubriformis for facilitating a multi-omics approach to identify novel, biologically conserved drug targets for five major GINs of veterinary importance. With this information, we were then able to demonstrate the potential of commercially available compounds as new anthelmintics.

Phylum Nematoda: a classification, catalogue and index of valid genera, with a census of valid species

A classification of the entire Phylum Nematoda is presented, based on current molecular, developmental and morphological evidence. The classification reflects the evolutionary relationships within the phylum, as well as significant areas of uncertainty, particularly related to the early evolution of nematodes.   It includes 3 classes, 8 subclasses, 12 superorders, 32 orders, 53 suborders, 101 superfamilies, 276 families, 511 subfamilies, 3030 genera, and 28537 species.   All valid species named from the time of publication of the previous classification and census (2010) to the end of 2019 are listed, along with the number of valid species in each genus.   Taxonomic authorities are provided for taxon names of all ranks.   The habitats where the species in each genus are found are listed, and an alphabetic index of genus names is provided.   The systematics of nematodes is reviewed, along with a history of nematode classification; evolutionary affinities and origins of nematodes; and the current diagnosis of the group.   Short overviews of the general biology, ecology, scientific and economic importance of the group are presented.  

Functional and phylogenetic uniqueness of helminth and flea assemblages of two South African rodents

The loss of a particular species from a community may have different effects on its functioning, depending on the presence or absence of functionally similar or phylogenetically close species in that community (redundancy). Redundancy is thus defined as the fraction of species diversity not expressed by functional or phylogenetic diversity. We assessed functional and phylogenetic alpha- and beta-redundancy in helminth and flea assemblages of two species of South African rodents, Rhabdomys dilectus and Rhabdomys pumilio, using community uniqueness as the inverse indicator of redundancy. We asked whether patterns of functional and phylogenetic alpha- and beta-uniqueness differed between (i) parasite groups (endo- versus ectoparasites), (ii) host species within parasite groups, and (iii) biomes within host species. We found differences between the two hosts in the functional and phylogenetic alpha-uniqueness (but not beta-uniqueness) of flea, but not helminth, assemblages. Significant correlations between the alpha-uniqueness of parasite assemblages and the total parasite prevalence were found only for phylogenetic uniqueness and only in helminths. Pairwise site-by-site dissimilarities in uniqueness (beta-uniqueness) and pairwise dissimilarity in prevalence were significantly associated (positively) in helminths but not in fleas. A between-biome difference in functional (but not phylogenetic) alpha-uniqueness was found in both helminth and flea assemblages harboured by R. pumilio. We conclude that the resilience of parasite assemblages in terms of the effect on hosts depends not only on their transmission strategy but also on traits of host species and environmental factors.

Boehmiella wilsoni (Nematoda, Heligmosomoidea, Boehmiellidae fam. nov.), found in Amazonian rodents

The genus Boehmiella was initially described as a member of the family Trichostrongylidae. Subsequently, it was assigned to the subfamily Haemonchinae in the family Haemonchidae. We analyzed parasites of spiny tree-rats, Mesomys hispidus, collected in the Amazon rainforest, which were identified as B. wilsoni based on integrative taxonomy. Using morphology, morphometry, and scanning electron microscopy (SEM), we added new data to the original description of the species. We also inferred phylogenetic hypotheses for its relationships within the Trichostrongylina, based on partial nuclear 18S and 28S rRNA genes, through Maximum Likelihood and Bayesian analyses. In conclusion, B. wilsoni does not belong to the family Haemonchidae, nor is it closely related to any other trichostrongylin family, and therefore, we propose the establishment of a new family, Boehmiellidae fam. nov., to which the genus Boehmiella is allocated.

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Helminth found in arboreal rodent of the Amazon region, with description of new host, new geographical distribution, new taxonomic data, and proposal of a new family to allocate the genus according to molecular and morphological analyses.

Evolution and Biogeography of Haemonchus contortus: Linking Faunal Dynamics in Space and Time

History is the foundation that informs about the nuances of faunal assembly that are essential in understanding the dynamic nature of the host-parasite interface. All of our knowledge begins and ends with evolution, ecology and biogeography, as these interacting facets determine the history of biodiverse systems. These components, relating to Haemonchus, can inform about the complex history of geographical distribution, host association and the intricacies of host-parasite associations that are played out in physiological and behavioural processes that influence the potential for disease and our capacity for effective control in a rapidly changing world. Origins and evolutionary diversification among species of the genus Haemonchus and Haemonchus contortus occurred in a complex crucible defined by shifts in environmental structure emerging from cycles of climate change and ecological perturbation during the late Tertiary and through the Quaternary. A history of sequential host colonization associated with waves of dispersal bringing assemblages of ungulates from Eurasia into Africa and processes emerging from ecosystems in collision and faunal turnover defined the arena for radiation among 12 recognized species of Haemonchus. Among congeners, the host range for H. contortus is exceptionally broad, including species among artiodactyls of 40 genera representing 5 families (and within 12 tribes of Bovidae). Broad host range is dramatically reflected in the degree to which translocation, introduction and invasion with host switching, has characterized an expanding distribution over time in North America, South America, southern Eurasia, Australia and New Zealand, coincidental with agriculture, husbandry and global colonization by human populations driven particularly by European exploration after the 1500s. African origins in xeric to mesic habitats of the African savannah suggest that historical constraints linked to ecological adaptations (tolerances and developmental thresholds defined by temperature and humidity for larval stages) will be substantial determinants in the potential outcomes for widespread geographical and host colonization which are predicted to unfold over the coming century. Insights about deeper evolutionary events, ecology and biogeography are critical as understanding history informs us about the possible range of responses in complex systems under new regimes of environmental forcing, especially, in this case, ecological perturbation linked to climate change. A deeper history of perturbation is relevant in understanding contemporary systems that are now strongly structured by events of invasion and colonization. The relaxation of abiotic and biotic controls on the occurrence of H. contortus, coincidental with inception and dissemination of anthelmintic resistance may be synergistic, serving to exacerbate challenges to control parasites or to limit the socioeconomic impacts of infection that can influence food security and availability. Studies of haemonchine nematodes contribute directly to an expanding model about the nature of diversity and the evolutionary trajectories for faunal assembly among complex host-parasite systems across considerable spatial and temporal scales.

Phylogenetic patterns of Haemonchus contortus and related trichostrongylid nematodes isolated from Egyptian sheep

Haemonchus contortus is a major parasite of small ruminants and its blood-feeding behaviour causes effects ranging from mild anaemia to death. Knowledge of the genetic variation within and among H. contortus populations can provide the foundation for understanding transmission patterns and aid in the control of haemonchosis. Adult male H. contortus were collected from three geographical regions in Egypt. The second internal transcribed spacer (ITS2) of nuclear ribosomal DNA was amplified using the polymerase chain reaction (PCR) and sequenced directly. The population genetic diversity and sequence variations were determined. Nucleotide sequence analyses revealed one genotype (ITS2) in all worms, without genetic differentiation. The similarity in population genetic diversity and genetic patterns observed among the three geographical regions could be attributed to possible movement between the sites. This is the first study of genetic variation in H. contortus in Egypt. The present results could have implications for the rapid characterization of H. contortus and other trichostrongyloid nematodes, and evaluation of the epidemiology of H. contortus in Egypt.

Exploring the Gastrointestinal "Nemabiome": Deep Amplicon Sequencing to Quantify the Species Composition of Parasitic Nematode Communities

Parasitic helminth infections have a considerable impact on global human health as well as animal welfare and production. Although co-infection with multiple parasite species within a host is common, there is a dearth of tools with which to study the composition of these complex parasite communities. Helminth species vary in their pathogenicity, epidemiology and drug sensitivity and the interactions that occur between co-infecting species and their hosts are poorly understood. We describe the first application of deep amplicon sequencing to study parasitic nematode communities as well as introduce the concept of the gastro-intestinal “nemabiome”. The approach is analogous to 16S rDNA deep sequencing used to explore microbial communities, but utilizes the nematode ITS-2 rDNA locus instead. Gastro-intestinal parasites of cattle were used to develop the concept, as this host has many well-defined gastro-intestinal nematode species that commonly occur as complex co-infections. Further, the availability of pure mono-parasite populations from experimentally infected cattle allowed us to prepare mock parasite communities to determine, and correct for, species representation biases in the sequence data. We demonstrate that, once these biases have been corrected, accurate relative quantitation of gastro-intestinal parasitic nematode communities in cattle fecal samples can be achieved. We have validated the accuracy of the method applied to field-samples by comparing the results of detailed morphological examination of L3 larvae populations with those of the sequencing assay. The results illustrate the insights that can be gained into the species composition of parasite communities, using grazing cattle in the mid-west USA as an example. However, both the technical approach and the concept of the ‘nemabiome’ have a wide range of potential applications in human and veterinary medicine. These include investigations of host-parasite and parasite-parasite interactions during co-infection, parasite epidemiology, parasite ecology and the response of parasite populations to both drug treatments and control programs.

Morphological aspects of Angiostrongylus costaricensis by light and scanning electron microscopy

Angiostrongylus costaricensis is a parasitic nematode that can cause severe gastrointestinal disease, known as abdominal angiostrongiliasis, in humans. This paper presents the characterization of first- and third-stage larvae and male and female adult worms of A. costaricensis by scanning electron and light microscopy. Several novel anatomical structures were identified by scanning electron microscopy, including details of the cuticular striations of the spicules in male worms and a protective flap of the cuticle covering the vulvar aperture in female worms. Other taxonomic features revealed by light microscopy include the gubernaculum and the esophageal-intestinal valve. The use of two microscopy techniques allowed a detailed characterization of the morphology of this nematode. A number of previously identified taxonomic features, such as the striated nature of the spicules and the lateral alae were confirmed; however, the use of scanning electron microscopy resulted in a reassessment of the correct number of papillae distributed around the oral opening and behind the cloacal opening. These observations, in combination with light microscopy-based characterization of the gubernaculum and esophageal valves, have allowed a more detailed description of this nematode taxonomy.

First description of gastrointestinal nematodes of Barbary sheep (Ammotragus lervia): the case of Camelostrongylus mentulatus as a paradigm of phylogenic and specific relationship between the parasite and its ancient host

The gastrointestinal helminth fauna of 24 Barbary sheep or Aoudad (Ammotragus lervia sahariensis) maintained in the Parque de Rescate de la Fauna Sahariana (PRFS, CSIC, Almeria, Spain) was analyzed. Most animals (87.5 %) were parasitized, and multiple infections were highly present. The following species were identified: Camelostrongylus mentulatus, Teladorsagia circumcincta, Marshallagia marshalli, Ostertagia ostertagi, O. leptospicularis, O. lyrata, Haemonchus contortus, Teladorsagia trifurcata, Trichostrongylus vitrinus, T. colubriformis, T. probolorus, T. capricola, Nematodirus spathiger, N. abnormalis, N. filicollis, N. helvetianus, Trichuris spp. and Skrjabinema ovis. Teladorsagia circumcincta was the most prevalent nematode in abomasum (52.6 %) followed by C. mentulatus (50 %). However, this latter nematode had the greater mean intensity and abundance. In the small intestine, T. colubriformis and T. vitrinus had the highest prevalence (36.4 %); the last one showed also the greater mean intensity and abundance. It should be emphasized the presence of Skrjabinema ovis (prevalence 39.1 %) in the large intestine, showing the greater mean abundance and intensity, although with a low values. Camelostrongylus mentulatus could be the most primitive nematode of the family trichostrongylidae recovered in this study; attending to its high prevalence, mean abundance and mean intensity, the possible specificity between this parasite and the Aoudad is discussed.

Genetic characterization of the blood-sucking nematodes Libyostrongylus dentatus and Libyostrongylus douglassii supports their different evolutionary history

Libyostrongylus sp. are nematodes that infect ostriches. Libyostrongylus douglassii was first described in ostriches from several countries in the world. Later Libyostrongylus dentatus was morphologically identified in ostriches in the USA and Brazil, and mixed infection is common in the latter country. The internal transcribed spacer (ITS) region of the ribosomal DNA gene is used for genetic variability assessment and phylogenetic reconstruction for many organisms. Through genetic analysis the status of different species morphologically defined was confirmed and a molecular method was developed to differentiate both species. ITS1, 5.8S, ITS2 regions of L. douglassii and L. dentatus were characterized. Regarding complete ITS region, the K2-p genetic distance between the species was 0.060 (SE 0.008) and the intra-specific distance was 0.002 (SE 0.001) for L. dentatus and 0.006 (SE 0.002) for L. douglassii. NJ and MP phylogenetic analysis of ITS1 and ITS2 regions indicated that both species belong to the Trichostrongylidae family, and are evolutionarily different, suported by high bootstrap value. Based on ITS DNA polymorphisms, a molecular approach was designed to detect both species. These results are the first molecular characterization of L. douglassii and L. dentatus, and provide new tools for the identification of these parasites of veterinary importance.

Development of Graphidium strigosum (Nematoda, Haemonchidae) in its natural host, the rabbit (Oryctolagus cuniculus) and comparison with several Haemonchidae parasites of ruminants

The morphogenesis (studied for the first time) and the chronology of the life cycle of Graphidium strigosum (Dujardin, 1845) were studied in detail in its natural host, Oryctolagus cuniculus. Naive rabbits were each infected per os with G. strigosum infective larvae (L3). Animals were euthanized each day for the first 10 days after infection (DAI), then every 2 days from 12 to 40 DAI. The free living period lasted 5-8 days at 24°C. By 1 DAI, all the larvae were exsheathed in the stomach. The third molt occurred between 9 and 17 DAI. The last molt occurred between 24 and 32 DAI. The prepatent period lasted 42-44 DAI, while the patent period lasted at least 13 months. For each experiment, the morphology of the different stages of the life cycle was described. The chronology of the G. strigosum life cycle and its morphogenesis were compared to those of different Haemonchidae parasites of ruminants (Ostertagia ostertagi, Teladorsagia circumcincta, Haemonchus contortus, and Haemonchus placei) in their natural hosts.

Morphogenesis and distribution of Trichostrongylus retortaeformis in the intestine of the rabbit

The morphogenesis and the distribution along the digestive tract of Trichostrongylus retortaeformis(Zeder, 1800) (Nematoda) were studied in detail in one of its natural hosts, Oryctolagus cuniculus. Worm-free rabbits were each infected with T. retortaeformis larvae and were killed at 12 h post-infection (HPI) and on each day from 1 to 15 days post-infection (DPI). The distribution of worm populations along the small intestine was assessed. At the different dates of infection, more than 80% of the population was recovered from the first third of the intestine with more than 50% occuring in the first 30 cm. For each date, morphological descriptions of the different stages of the life cycle were also provided. In addition, adult worms collected from naturally infected rabbits from France were redescribed.

Spiculopteragia mathevossianiRuchliadev, 1948 is the minor morph ofSpiculopteragia spiculoptera(Gushanskaya, 1931): molecular evidence

Although Spiculopteragia spiculoptera is primarily a parasite of cervids, it can also but less often contaminate domestic livestock. Little is known about its epidemiology and its pathogenicity in domestic ruminants and other unusual cervid species. Its taxonomic status remains unclear since the hypothesis of morphological polymorphism among males has been proposed. However, accurate taxonomy is fundamental in the identification and survey of potentially pathogenic species of parasites. The second internal transcribed spacer of rDNA (ITS-2) and the mitochondrial (mt) DNA-derived ND4 gene were used to study the polymorphism hypothesis for S. spiculoptera. ND4 evolves more quickly than ITS-2 and is considered to be more discriminant in the characterization of closely related species. DNA sequences of ITS-2 and ND4 were studied in 18 individual males of morphological type spiculoptera and in 3 of morphological type of mathevossiani from Red deer (Cervus elaphus), Roe deer (Capreolus capreolus) and Chamois (Rupicapra rupicapra). Intraindividual ITS-2 variations were detected within and between each morphotype of Spiculopteragia but these differences did not separate the two morphs mathevossiani and spiculoptera. Similarly, although ND4 showed a high level of nucleotide substitution, the morphotypes S. mathevossiani and S. spiculoptera were clustered together. Our genetic data support the dimorphic male hypothesis for the species S. spiculoptera.

Phylogeny for genera of Nematodirinae (Nematoda: Trichostrongylina)

Monophyly for the Nematodirinae, with 5 genera, Murielus, Rauschia, Nematodiroides, Nematodirus, and Nematodirella was confirmed based on comparative morphology and phylogenetic analysis of structural characters. This concept for the nematodirines excludes the monotypic Lamanema chavezi, but otherwise corroborates generic-level diversity as defined in prior studies. Exhaustive analysis resulted in 1 most parsimonious tree (36 steps; consistency index [CI] = 0.94; retention index [RI] = 0.93; excluding phylogenetically uninformative characters, CI = 0.92). As an inclusive or monophyletic group, Nematodirinae was diagnosed by 8 synapomorphies (7 are unequivocal): (1) large eggs, (2) long filiform spicules, (3) basal division of the dorsal ray, (4) symmetrical membrane enveloping the spicule tips, (5) fused structure of the spicule tips, (6) absence of the gubernaculum, (7) development of the third-stage larva within the egg, and (8) ornamentation in the form of discrete bosses on the bursa. Exclusion of Lamanema will require new assessments of historical biogeography and the evolution of host associations for the nematodirines.

Pseudostertagia bullosa (Nematoda: Trichostrongyloidea) in artiodactyl hosts from North America: redescription and comments on systematics

A relationship for Pseudostertagia bullosa within the trichostrongyloids has been enigmatic or unresolved. Studies of the synlophe in males and females of P. bullosa revealed a tapering system anterior to the deirids and a pattern of parallel ridges extending to near the caudal extremity in both lateral and median fields. Structurally, the synlophe differs considerably from that seen among the Cooperiinae and exhibits homoplasy with respect to ridge systems among some Ostertagiinae. Other structural characters due to symplesiomorphy, homoplasy or because they represent autapomorphies do not serve to reveal the putative relationships for P. bullosa with other trichostrongyloids. Although somewhat equivocal, the 2-2-1 pattern of the bursa and position of rays 2 and 3 suggest an association with the Cooperinae, as postulated by Durette-Desset and others. Pseudostertagia bullosa appears to be a species that has survived in the pronghorn, Antilocapra americana, a relictual pecoran artiodactyl that occurs in xeric regions of western North America; pronghorn are the sole remnant of the late Tertiary radiation for Antilocapridae across North America. Pseudostertagia bullosa may occur in mixed infections with a number of ostertagiines in the abomasa of mule deer (Odocoileus hemionus) and domestic sheep (Ovis aries) in regions of sympatry for pronghorn and these artiodactyl hosts.

Helminth parasites of the grassland melomys (Muridae : Hydromyinae) from Australia and Papua New Guinea

This study documents the helminth assemblages of grassland melomys: Melomys burtoni (Ramsay, 1887), Melomys sp. cf. burtoni and Melomys lutillus (Thomas, 1913). In total, 22 helminth species comprising one cestode and 21 nematodes from 112 hosts were found. All the specimens of Physaloptera spp. examined proved to be Physaloptera banfieldi Johnston & Mawson, 1941 with P. troughtoni Johnston & Mawson, 1941 the junior synonym. The dominant helminth group was the trichostrongyloid nematodes including Odilia melomyos (Mawson, 1961) and O. mackerrasae (Mawson, 1961). The most prevalent, O. melomyos, occurred in each of the host species across all areas sampled (New South Wales, Northern Territory, Papua New Guinea, Queensland and Western Australia). The helminth assemblage of M. burtoni from hosts from New South Wales and Queensland was the most diverse. The helminths of M. burtoni from the Northern Territory and of M. lutillus from Papua New Guinea were subsets of that assemblage. That of M. cf. burtoni from Western Australia, with only six helminth species, was not dominated by trichostrongyloids, three of the six species were not found in other localities, and, with Sorensen’s Indices of 18.2% when compared with the helminths from Papua New Guinea and the Northern Territory and 24% when compared with Queensland, was the least similar. No substantial differences were found between the helminth assemblages of the grassland melomys group, excluding M. cf. burtoni, and Melomys cervinipes (Gould, 1852), the fawn footed melomys. This was reflected in a Sorensen’s Index of 67.9%. The time between the arrival of Melomys into Australia during the Pleistocene and the present day suggests that the trichostrongyloids O. melomyos, O. mackerrasae and O. mawsonae (Durette-Desset, 1969) may have travelled with their rodent hosts from New Guinea to Australia and other helminths in the assemblage may have been acquired in Australia.

PHYLOGENY FOR SPECIES OF HAEMONCHUS (NEMATODA: TRICHOSTRONGYLOIDEA): CONSIDERATIONS OF THEIR EVOLUTIONARY HISTORY AND GLOBAL BIOGEOGRAPHY AMONG CAMELIDAE AND PECORA (ARTIODACTYLA)

Phylogenetic analysis of 25 morphological characters among the 12 species of Haemonchus resulted in 1 most parsimonious tree (60 steps; consistency index = 0.67, retention index = 0.80). Monophyly for Haemonchus was diagnosed by 3 unequivocal synapomorphies, including the asymmetric origin of the dorsal ray, relative size of the ventral rays, and the presence of a barb on each spicule tip. Species of Haemonchus have complex histories with respect to host and geographic associations: (1) origins in Africa with basal diversification in antelopes (H. krugeri, H. lawrencei, H. dinniki, H. horaki), (2) independent events of colonization for those species in Caprini and Bovinae (H. contortus, H. placei, H. bedfordi, H. similis), (3) colonization and development of core host associations within Camelidae (H. longistipes) and among Antilopinae, Tragelaphini, and Giraffidae (H. mitchelli, H. okapiae, H. vegliai), and (4) geographically widespread species that are represented only by those that have been translocated with domestic stock. The North American fauna is characterized by 3 introduced and exotic species, H. placei, H. contortus, H. similis, which emphasizes the importance of continued documentation of faunal diversity in the context of predictive foundations derived from phylogenetic studies. Satellite associations for species of Haemonchus, particularly among Cervidae and Camelidae in the Neotropics and Cervidae, Antilocapridae, and possibly wild Caprinae in the Nearctic, have been a consequence of introductions and exchange of parasites at historical interfaces for managed and natural ecosystems. Such distributions are emblematic of the overriding significance of anthropogenic factors as determinants of the global distributions for pathogenic parasites in domestic and wild ruminants.

Phylogenetic analysis of the Metastrongyloidea (Nematoda: Strongylida) inferred from ribosomal RNA gene sequences

Phylogenetic relationships among nematodes of the strongylid superfamily Metastrongyloidea were analyzed using partial sequences from the large-subunit ribosomal RNA (LSU rRNA) and small-subunit ribosomal RNA (SSU rRNA) genes. Regions of nuclear ribosomal DNA (rDNA) were amplified by polymerase chain reaction, directly sequenced, aligned, and phylogenies inferred using maximum parsimony. Phylogenetic hypotheses inferred from the SSU rRNA gene supported the monophyly of representative taxa from each of the 7 currently accepted metastrongyloid families. Metastrongyloid taxa formed the sister group to representative trichostrongyloid sequences based on SSU data. Sequences from either the SSU or LSU RNA regions alone provided poor resolution for relationships within the Metastrongyloidea. However, a combined analysis using sequences from all rDNA regions yielded 3 equally parsimonious trees that represented the abursate Filaroididae as polyphyletic, Parafilaroides decorus as the sister species to the monophyletic Pseudaliidae, and a sister group relationship between Oslerus osleri and Metastrongylus salmi. Relationships among 3 members of the Crenosomatidae, and 1 representative of the Skrjabingylidae (Skrjabingylus chitwoodorum) were not resolved by these combined data. However, members of both these groups were consistently resolved as the sister group to the other metastrongyloid families. These relationships are inconsistent with traditional classifications of the Metastrongyloidea and existing hypotheses for their evolution.

OVEJECTOR STRUCTURE IN THE HAEMONCHINAE (NEMATODA:TRICHOSTRONGYLOIDEA) OF RUMINANTS

The use of ovejector structure in the phylogeny of the Haemonchinae is hampered by differences among nematologists in the application of terminology and the recognition of homologous parts. Some workers recognize a sphincter with 2 parts, but others recognize only the proximal, rounded part of the sphincter and include the distal cylindrical part of the sphincter with the vestibule. The results of this study demonstrate that all sphincters of Haemonchinae of ruminants have 2 parts. To encourage the application of a uniform terminology to homologous parts of the ovejector, we propose the use of the terms "sphincter 1" for the rounded part and "sphincter 2" for the cylindrical part. It is hoped that clarification of the terminology for ovejectors of the Haemonchinae will provide a model useful for improving descriptions of ovejectors throughout the Trichostrongyloidea.

Development of Trichostrongylus colubriformis and Trichostrongylus vitrinus, parasites of ruminants in the rabbit and comparison with Trichostrongylus retortaeformis

The parasitic phase of development of both Trichostrongylus colubriformis and Trichostrongylus vitrinus, parasites of ruminants, was studied in detail in the rabbit. In T. colubriformis, the third moult appeared by 4 days after infection (DAI) and the last moult occurred between 10 and 11 DAI. In T. vitrinus, the third moult occurred between 8 and 11 DAI and the last one between 12 and 15 DAI. The prepatent period lasted 16-17 days for T. colubriformis and 20 days for T. vitrinus. The chronology of the life cycles and the distribution of the parasites along the small intestine for various Trichostrongylus spp. from lagomorphs and ruminants in the natural host or in the experimental host were compared. All of these biological parameters indicated a lower level of adaptation of T. vitrinus compared to the other species of Trichostrongylus. The results are fully compatible with the evolutionary scheme based on morphological analyses.

Intestinal migrations of Trichostrongylus retortaeformis (Trichostrongylina, Trichostrongylidae) in the rabbit

Observations were made on histological sections of the stomach and small intestine of seven rabbits infected with Trichostrongylus retortaeformis and from one uninfected control rabbit. At 12h post-infection, larvae were found in the small intestine. At first, only a few larvae were observed entering the mucosa through capillaries of the stroma of villi; the majority of larvae remained in the intestinal lumen, within mucus of the crypts. We consider that the presence of the worms in the stroma is the result of a larval migration. From a phyletic point of view, this migration is interpreted as an ancestral memory of the pulmonary migration seen in the primitive Strongylida.

Phylogeny of the Trichostrongylina (Nematoda) inferred from 28S rDNA sequences

We produced a molecular phylogeny of species within the order Strongylida (bursate nematodes) using the D1 and D2 domains of 28S rDNA, with 23 new sequences for each domain. A first analysis using Caenorhabditis elegans as an outgroup produced a tree with low resolution in which three taxa (Dictyocaulus filaria, Dictyocaulus noerneri, and Metastrongylus pudendotectus) showed highly divergent sequences. In a second analysis, these three species and C. elegans were removed and an Ancylostomatina, Bunostomum trigonocephalum, was chosen (on the basis of previous morphological analyses) as the outgroup for an analysis of the phylogenetic relationships between and within the Strongylina (strongyles) and Trichostrongylina (trichostrongyles). A very robust tree was obtained. The Trichostrongylina were monophyletic, but the Strongylina were paraphyletic, though this requires confirmation. Within the Trichostrongylina, the three superfamilies defined from morphological characters are confirmed, with the Trichostrongyloidea sister group to a clade including the Molineoidea and Heligmosomoidea. Within the Trichostrongyloidea, the Cooperiidae, Trichostrongylidae, and Haemonchidae were polytomous, the Haemonchinae were monophyletic, but the Ostertagiinae were paraphyletic. The sister-group relationships between Molineoidea and Heligmosomoidea were unsuspected from previous morphological analysis. No unequivocal morphological synapomorphy could be found for the grouping Molineoidea + Heligmosomoidea, but none was found which contradicted it.

Evolutionary relationships of trichostrongyloid nematodes (Strongylida) inferred from ribosomal DNA sequence data

The evolutionary relationships of 21 species of trichostrongyloid nematodes were determined by use of sequence data of the second internal transcribed spacer of the ribosomal DNA aligned according to secondary structure information. Irrespective of the method of analysis used, the topologies of the phylogenetic trees derived from the molecular data differed with respect to all four hypotheses proposed previously for the evolutionary relationships of the different subfamilies within the Trichostrongylidae based on morphological data. Thus, the molecular data set did not resolve the conflict between the four previous proposals for the subfamilial relationships. Nonetheless, all trees derived from the molecular data showed strong support for the exclusion of the genera Filarinema and Amidostomum from the clade containing the species within the family Trichostrongylidae. This represents a major difference from the most recent proposal of the systematics of the Trichostrongyloidea in which these two genera were included within the Trichostrongylidae. Therefore, the molecular data support an earlier systematic framework in which Filarinema and Amidostomum were considered to be sister groups of the Trichostrongyloidea.

Phylogenetic relationships among species of Stilestrongylus Freitas, Lent and Almeida, 1937 (Trichostrongyloidea: Heligmonellidae: Nippostrongylinae), parasites of myomorph rodents (Rodentia: Muridae) in the Neotropics

The phylogenetic relationships of 14 species of Stilestrongylus were analyzed using the comparative morphology of 21 characters. We obtained 2 shortest trees of 50 steps, with a consistency index of 0.540 and 25 apomorphic character states. Ingroup monophyly was supported on these trees by 2 and 3 synapomorphies, respectively, and the ingroup was defined by the following characters: greater number of ventral ridges relative to the number of ridges dorsally, asymmetric bursa, and externodorsal rays differing in size. Sister-group relationships among Stilestrongylus and the other genera designated as outgroups are relatively consistent with those postulated by Durette-Desset's in a classification of the Nippostrongylinae. The ancestor of the species groups comprising Hassalstrongylus, Guerrerostrongylus, and Stilestrongylus originated and diversified in murids in the Neotropical region. Species of Hassalstrongylus occur in rodents between southeastern North America and the eastern part of South America (Brazil and Argentina), whereas species of Guerrerostrongylus and Stilestrongylus diversified exclusively in rodents in the Neotropics.

Synlophe patterns of the Haemonchinae of ruminants (Nematoda: Trichostrongyloidea)

The pattern of longitudinal ridges (synlophe) on the external cuticular surface of trichostrongylid nematodes has been shown to be of value for distinguishing species and determining relationships among higher taxa. In the process of studying Mecistocirrus digitatus, the large stomach worm of bovids of Asia that has been imported and established in the Americas, we observed remarkably similar synlophe patterns to those described for 3 species of Haemonchus and to those we examined in a species of Ashworthius. In all 3 genera, the synlophe is absent from the posterior part of the body. Only in Haemonchus does the synlophe extend beyond midbody. In both M. digitatus and Ashworthius sidemi, the synlophe extends posteriorly only about 1/4 of body length. In all 3 genera, the synlophe consists of about 30 ridges in the region of the esophagus with variation among species in specific areas, including additional pairs of subventral and subdorsal ridges and different lengths of sublateral ridges. This information is useful for identifying species and determining relationships among these large stomach worm parasites of cattle, sheep, goats, and farmed and wild cervids.

Genomic and genetic research on bursate nematodes: significance, implications and prospects

Molecular genetic research on parasitic nematodes (order Strongylida) is of major significance for many fundamental and applied areas of medical and veterinary parasitology. The advent of gene technology has led to some progress for this group of nematodes, particularly in studying parasite systematics, drug resistance and population genetics, and in the development of diagnostic assays and the characterisation of potential vaccine and drug targets. This paper gives an account of the molecular biology and genetics of strongylid nematodes, mainly of veterinary socio-economic importance, indicates the implications of such research and gives a perspective on genome research for this important parasite group, in light of recent technological advances and knowledge of the genomes of other metazoan organisms.