Genetic evidence indicating that Cooperia surnabada and Cooperia oncophora are one species

A Revised Checklist of Cooperia Nematodes (Trichostrogyloidea), Common Parasites of Wild and Domestic Ruminants

This review updates the current knowledge on the taxonomy of intestinal nematodes of the genus Cooperia parasitizing in wild and domestic ruminants. The emphasis is put on revision of 19 valid species belonging to the genus. This analysis focuses on main features of the genus Cooperia, including its geographic occurrence and the life cycle details. The most widespread congeners are Cooperia curticei, C. oncophora, C. pectinata, and C. punctata, having nearly worldwide distribution. The fifth species, referred by electronic databases from the European territory as Cooperia asamatiSpiridonov, 1985, is unveiled here originally as nomen nudum.

Mitochondrial genome evidence suggests Cooperia sp. from China may represent a distinct species from Cooperia oncophora from Australia

Cooperia spp. are parasitic nematodes parasitizing in small intestine of ruminants with a worldwide distribution. Infection of ruminants with Cooperia species can cause severe enteritis, causing significant socio-economic losses to the livestock industry. However, it is yet to know whether there is genetic diversity in mitochondrial (mt) DNA sequences of Cooperia nematodes from different geographic regions. The objective of the present study was to examine sequence difference in mt genomes between Cooperia sp. from China and other Cooperia species. We determined the sequences of the internal transcribed spacer (ITS-1 and ITS-2) of nuclear ribosomal DNA (rDNA) of 11 Cooperia specimens collected from the small intestine of a Tianzhu White yak in Gansu Province, northwestern China, which had 99% similarity with that of C. oncophora from Brazil (GenBank accession Number: AJ544290) in ITS-1, and 99% similarity with those from Denmark (AB245040), Scotland and Australia (AJ000032) in ITS-2, indicating that specimens used in the present study should at least represent parasites in Cooperia. We then determined the complete mt genome sequences of one representative specimen of Cooperia sp. from China (CspC), compared the mt DNA sequences with that of C. oncophora from Australia (COA, GQ888713), and conducted phylogenetic analysis with selected nematodes using both maximum likelihood (ML) and Bayesian inference (BI) methods based on both concatenated 12 PCGs, rrnL and rrnS sequences and partial cox2 sequences. The complete mt genome sequence of CspC (KY769271) is 13, 583 bp in length, which is 91 bp shorter than that from COA. The sequence difference over the entire mt genome between CspC and COA was 12.2% in nucleotide and 6.3% in inferred amino acids, with nad4L and nad1 being the most variable and the most conserved PCGs, respectively. Phylogenetic analysis indicated that CspC and COA were closely-related but distinct taxa. The determination of mt genome sequences for Cooperia sp. from China also provides novel resources for further studies of taxonomy, systematics and population genetics of Cooperia from different geographical locations.

Molecular marker sequences of cattle Cooperia species identify Cooperia spatulata as a morphotype of Cooperia punctata

The genus Cooperia includes important parasites of ruminants and currently contains 34 accepted species. However, even for those species infecting livestock, there is a considerable lack of molecular information and many species are only identifiable using subtle morphological traits. The present study aimed to provide molecular data to allow diagnosis of Cooperia species infecting cattle. Partial sequences of two mitochondrial (cytochrome oxidase 2, 12S rRNA gene) and two nuclear genes (isotype 1 β tubulin gene including two introns, internal transcribed spacers (ITS) were obtained from morphologically identified specimens of Cooperia pectinata, Cooperia punctata and Cooperia spatulata as well as from larvae of pure Cooperia oncophora and C. punctata laboratory isolates. Pairwise identity of ITS-2 sequences was very high and it was the only region able to identify a specimen as Cooperia sp. However, the ITS-2 was unreliable for diagnosis at the species level. All other marker sequences could not unequivocally be allocated to the genus Cooperia but allowed clear species identification with the exception of the pair C. punctata/C. spatulata for which no significant differences were found for any marker sequence. Maximum-likelihood phylogenetic analyses of individual genes as well as a multi-locus analysis covering all four sequences confirmed that specimen identified as C. spatulata were randomly distributed throughout the C. punctata cluster and formed no group of their own. In contrast, the other Cooperia species formed clearly separated and statistically supported clusters. These data indicate that C. spatulata is most likely only a morphotype of C. punctata and the name should be considered a synonym. Combinations of nuclear and mitochondrial markers should be used to identify morphotypes or cryptic species to benefit from excellent barcoding properties of the latter but allowing proper phylogenetic analyses and controlling for lineage sorting that might occur for mitochondrial genotypes within a species.

Morphological variability and molecular identification of Uncinaria spp. (Nematoda: Ancylostomatidae) from grizzly and black bears: new species or phenotypic plasticity?

The hookworms Uncinaria rauschi Olsen, 1968 and Uncinaria yukonensis ( Wolfgang, 1956 ) were formally described from grizzly ( Ursus arctos horribilis) and black bears ( Ursus americanus ) of North America. We analyzed the intestinal tracts of 4 grizzly and 9 black bears from Alberta and British Columbia, Canada and isolated Uncinaria specimens with anatomical traits never previously documented. We applied morphological and molecular techniques to investigate the taxonomy and phylogeny of these Uncinaria parasites. The morphological analysis supported polymorphism at the vulvar region for females of both U. rauschi and U. yukonensis. The hypothesis of morphological plasticity for U. rauschi and U. yukonensis was confirmed by genetic analysis of the internal transcribed spacers (ITS-1 and ITS-2) of the nuclear ribosomal DNA. Two distinct genotypes were identified, differing at 5 fixed sites for ITS-1 (432 base pairs [bp]) and 7 for ITS-2 (274 bp). Morphometric data for U. rauschi revealed host-related size differences: adult U. rauschi were significantly larger in black bears than in grizzly bears. Interpretation of these results, considering the historical biogeography of North American bears, suggests a relatively recent host-switching event of U. rauschi from black bears to grizzly bears which likely occurred after the end of the Wisconsin glaciation. Phylogenetic maximum parsimony (MP) and maximum likelihood (ML) analyses of the concatenated ITS-1 and ITS-2 datasets strongly supported monophyly of U. rauschi and U. yukonensis and their close relationship with Uncinaria stenocephala (Railliet, 1884), the latter a parasite primarily of canids and felids. Relationships among species within this group, although resolved by ML, were unsupported by MP and bootstrap resampling. The clade of U. rauschi, U. yukonensis, and U. stenocephala was recovered as sister to the clade represented by Uncinaria spp. from otariid pinnipeds. These results support the absence of strict host-parasite co-phylogeny for Uncinaria spp. and their carnivore hosts. Phylogenetic relationships among Uncinaria spp. provided a framework to develop the hypothesis of similar transmission patterns for the closely related U. rauschi, U. yukonensis, and U. stenocephala.

Activity of ivermectin long-acting injectable (IVOMEC(®) GOLD) in first-season grazing cattle exposed to natural challenge conditions in Germany

The persistent activity of ivermectin long-acting injection (IVM LAI; IVOMEC® GOLD, Merial; 3.15% ivermectin w/v) against nematode infections of cattle was evaluated under natural challenge conditions. Seventy nematode-free Brown Swiss calves were blocked by pre-treatment bodyweight and allocated randomly to seven groups of 10 animals each: saline (control) at 1 mL/50 kg bodyweight once on day 0 or IVM LAI at 1 mL/50 kg bodyweight (630 mcg IVM/kg) on either days 0, 7, 14, 21, 28, or 35. After housing until day 35, calves were grazed as one herd on a naturally contaminated pasture for 42 days. Calves were then weighed and housed for 4 weeks before being necropsied for parasite counting. Treatment with IVM LAI prevented the establishment (>90%, p < 0.05) of Dictyocaulus viviparus (100%), Bunostomum phlebotomum (100 %), Haemonchus contortus (98.6%), Ostertagia ostertagi/lyrata (94.9%), and Oesophagostomum radiatum (93.3%) for at least 77 days; Ostertagia leptospicularis (99.1%) for 63 days; Cooperia punctata (97.7%), Trichostrongylus axei (96.5%), and Ostertagia spp. inhibited larvae 4 (93.3%) for 56 days; Cooperia oncophora/surnabada (96.9%), Trichuris discolor (93.6%), and Cooperia spp. inhibited larvae 4 (98.8%); and Nematodirus spp. inhibited larvae 4 (97.1%) for 42 days. Calves of groups treated with IVM LAI had significantly (p < 0.001) higher days 0 to 77 weight gains than the saline-treated controls (28.40-39.25 vs 2.60 kg); the weight gains of the IVM LAI-treated groups, however, were not different from one another (p > 0.3). This study demonstrated a very high efficacy of IVOMEC® GOLD in preventing the establishment of a wide range of bovine nematodes for extended periods of time which was associated with a significant benefit to productivity in terms of weight gain.

Real-time PCR detection for quantification of infection levels with Ostertagia ostertagi and Cooperia oncophora in cattle faeces

A quantitative real-time polymerase chain reaction (qPCR) based on hydrolysis (TaqMan) probes is described for robust and sensitive detection of the infection levels with eggs and third stage larvae (L3) of Cooperia oncophora and Ostertagia ostertagi isolated from cattle faeces. The current microscopic method for identification of strongyle nematodes in cattle faeces is labour-intensive where reliable species determination also requires trained expertise, which is increasingly lacking. The goal of this study was to develop a sustainable non-labour intensive diagnostic qPCR assay to detect and determine the levels of infection with the two most common gastro-intestinal nematodes (GIN) in cattle faeces targeting the second internal transcribed spacer of nuclear ribosomal DNA (ITS2) region (rDNA). According to our results, this procedure allows to reliably detect the relative proportions of eggs and L3 for each of the two species. This assay produced consistent results when mixtures with known numbers of L3 of both species were tested, although it was also demonstrated that the calculated copy numbers of ITS2 between single L3 sometimes varied very much. In addition, a positive correlation (r(2)=0.23) between the proportion of eggs and L3 in different paired samples collect in the field was observed for both species. Thus, for the first time a qPCR assay is reported, which can discriminate between the two most important cattle nematode parasites in temperate regions. This is of major importance to the livestock sector as it can be used with great precision to demonstrate strategic treatment efficacy that is important for the detection of anthelmintic resistance (AR).

A combined microscopic-molecular method for the diagnosis of strongylid infections in sheep

We evaluated a combined microscopic-molecular approach for the diagnosis of key strongylid infections in sheep using panels of well-defined control and test samples. The method established is based on the separation of nematode eggs from faecal samples using a salt flotation procedure, the extraction and column-purification of genomic DNA, followed by real-time PCR and melting-curve analysis. Specific and semi-quantitative amplification from (a minimum of 0.1-2.0pg) genomic DNA of Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus spp., Cooperia oncophora, Oesophagostomum columbianum, Oesophagostomum venulosum or Chabertia ovina is achieved using a specific, forward oligonucleotide primer located in the second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA (rDNA) together with a conserved reverse primer in the large subunit of rDNA. Using a panel of well-defined genomic DNA samples from eggs from sheep monospecifically infected with H. contortus or Te. circumcincta, there was a correlation between cycle threshold (Ct) values in the PCR and numbers of egg per gram of faeces, thus allowing the semi-quantitation of parasite DNA in faeces. The findings of the present study indicate that a microscopic-molecular approach provides a useful tool for diagnosis, for epidemiological and ecological surveys as well as for integration into parasite monitoring, drug resistance (i.e. 'egg count reduction') testing or control programmes, particularly following semi- or full-automation.

PCR-based Species-Specific Amplification of ITS of Mecistocirrus digitatus and Its Application in Identification of GI Nematode Eggs in Bovine Faeces

Differential diagnosis of Mecistocirrus digitatus infection relies on morphological examination of either eggs in faecal samples or L3 larvae developed in vitro. Technical limitations hinder the practicability of these approaches. Hence, in order to develop a specific diagnostic measure for M. digitatus infection, we determined the sequence of the internal transcribed spacer (ITS) of its ribosomal DNA (rDNA) and designed primers for PCR-based species-specific amplification of the ITS to differentiate between M. digitatus and other common gastrointestinal (GI) nematode species. The newly designed primers amplified a single specific 520 base pair (bp) fragment from the M. digitatus ITS, and its detection limit was as low as 0.001 ng. Further, this sensitivity suggested that the specific fragment could be amplified even from a unicellular egg that collected directly from uteri of an adult M. digitatus female. In fact, we designed a method that employs a small piece of a cover slip and a filter paper by which we could differentially amplify a PCR fragment from a unicellular egg. The reliability of the specific PCR assay was also demonstrated with 10 oval samples that collected from bovine faeces by using sugar flotation method. These data suggested that the specific PCR assay of the ITS region of M. digitatus rDNA could be useful for the identification of GI nematodes.

The use of nuclear ribosomal DNA markers for the identification of bursate nematodes (order Strongylida) and for the diagnosis of infections

Many bursate nematodes are of major importance to animal health. Animals are often parasitized by multiple species that differ in their prevalence, relative abundance and/or pathogenicity. Implementation of effective management strategies for these parasites requires reliable methods for their detection in hosts, identification to the species level and measurement of intensity of infection. One major problem is the difficulty of accurately identifying and distinguishing many species of bursate nematode because of the remarkable morphological similarity of their eggs and larvae. The inability to identify, with confidence, individual nematodes (irrespective of their life-cycle stage) to the species level by morphological methods has often led to a search for species-specific genetic markers. Studies over the past 15 years have shown that sequences of the internal transcribed spacers of ribosomal DNA provide useful genetic markers, providing the basis for the development of PCR-based diagnostic tools. Such molecular methods represent powerful tools for studying the systematics, epidemiology and ecology of bursate nematodes and, importantly, for the specific diagnosis of infections in animals and humans, thus contributing to improved control and prevention strategies for these parasites.

GEOGRAPHIC DISTRIBUTION OF THE MUSCLE-DWELLING NEMATODE PARELAPHOSTRONGYLUS ODOCOILEI IN NORTH AMERICA, USING MOLECULAR IDENTIFICATION OF FIRST-STAGE LARVAE

Molecular identification of dorsal-spined larvae (DSL) from fecal samples indicates that the protostrongylid parasite Parelaphostrongylus odocoilei occupies a broader geographic range in western North America than has been previously reported. We analyzed 2,124 fecal samples at 29 locations from thinhorn sheep (Ovis dalli dalli and O. d. stonei), bighorn sheep (Ovis canadensis canadensis and O. c. californiana), mountain goats (Oreamnos americanus), woodland caribou (Rangifer tarandus caribou), mule deer (Odocoileus hemionus hemionus), and black-tailed deer (O. h. columbianus). The DSL were recovered from populations of thinhorn sheep south, but not north, of the Arctic Circle, and they were not recovered from any of the bighorn sheep populations that we examined. In total, DSL were recovered from 20 locations in the United States and Canada (Alaska, Yukon Territory, Northwest Territories, British Columbia, Alberta, and California). The DSL were identified as P. odocoilei by comparing sequences of the second internal transcribed spacer (ITS2) region of ribosomal RNA among 9 protostrongylid species validated by adult comparative morphology. The ITS2 sequences were markedly different between Parelaphostrongylus and other protostrongylid genera. Smaller fixed differences served as diagnostic markers for the 3 species of Parelaphostrongylus. The ITS2 sequences (n = 60) of P. odocoilei were strongly conserved across its broad geographic range from California to Alaska. Polymorphism at 5 nucleotide positions was consistent with multiple copies of the ITS2 within individual specimens of P. odocoilei. This work combines extensive fecal surveys, comparative morphology, and molecular diagnostic techniques to describe comprehensively the host associations and geographic distribution of a parasitic helminth.

Molecular epidemiological survey on the vectors of Thelazia gulosa, Thelazia rhodesi and Thelazia skrjabini (Spirurida: Thelaziidae)

A Polymerase Chain Reaction (PCR)- based assay developed for the specific identification of Thelazia gulosa, Thelazia rhodesi and Thelazia skrjabini (Nematoda, Spirurida), which cause bovine ocular thelaziosis, was evaluated for its usefulness in detecting the intermediate hosts and in estimating the infection prevalence of vectors in field conditions throughout 5 years (from 1997 to 2001). A total of 5190 flies were captured and identified as Musca larvipara, Musca osiris, Musca autumnalis, Musca tempestiva or Musca domestica. Genomic DNA was extracted from pools constituted by heads, thoraces, abdomens and wings of 10 flies of each species, and 2076 samples were subjected to a PCR assay to specifically detect the ribosomal ITS-1 sequence of bovine Thelazia. Amplicons were sequenced and subjected to digestion with CpoI restriction enzyme. M. autumnalis, M. larvipara, M. osiris and M. domestica species were shown to be PCR positive. T. gulosa was specifically detected by PCR in M. autumnalis, M. larvipara, M. osiris and M. domestica, whereas T. rhodesi is in M. autumnalis and M. larvipara. Of 27 positive samples, 23 were positive for T. gulosa and 4 for T. rhodesi, with a mean prevalence of 2·86% in the whole fly population collected. The highest mean prevalence values of infection were detected in M. autumnalis (4·46%) and M. larvipara (3·21%), and the former species was confirmed to be the vector of T. gulosa and T. rhodesi. This study is the first report of M. osiris as a vector of T. gulosa and M. larvipara as a vector of T. gulosa and T. rhodesi under natural conditions. The occurrence of Thelazia in fly populations in the Apulia region of Italy (in the 5 grazing seasons considered) indicates that cattle thelaziosis is enzootic in southern Italy. This molecular assay should be a useful epidemiological tool for assessing the role of different species of flies as intermediate hosts of thelaziae.

Cytochrome oxidase c subunit 1 polymorphisms show significant differences in distribution between a laboratory maintained population and a field isolate of Cooperia oncophora

A 474 bp fragment of the mitochondrial cytochrome oxidase c subunit 1 (cox1) of Cooperia oncophora was cloned and sequenced. The overall nucleotide diversity of the cox1 fragment varied from 0.5 to 2.0% between individuals. Two nucleotide substitutions were found within two RsaI endonuclease restriction sites and were used in a PCR-based restriction fragment length polymorphism (PCR-RFLP) assay to asses the intra-population variation of C. oncophora. Testing 816 individuals revealed the existence of three different haplotypes, having either both (type I) or only one (types II and III) RsaI site. Laboratory maintained individuals obtained at different time points after infection showed no significant difference in the distribution of the three haplotypes. Neither was there a difference in the distribution between male and female worms, confirming that the mitochondrial genome of C. oncophora is also maternally inherited. Nevertheless, there was a significant difference in the prevalence of the RsaI point mutation in the cox1 gene between the laboratory maintained population of C. oncophora and a Dutch field isolate, indicating that these RFLPs can be used to study genetic variation within or among C. oncophora populations.

Applications of single-strand conformation polymorphism (SSCP) to taxonomy, diagnosis, population genetics and molecular evolution of parasitic nematodes

The analysis of genetic variation in parasitic nematodes has important implications for studying aspects of taxonomy, diagnosis, population genetics, drug resistance and molecular evolution. This article highlights some applications of PCR-based single-strand conformation polymorphism (SSCP) for the analysis of sequence variation in individual parasites (and their populations) to address some of these areas. It also describes the principles and advantages of SSCP, and provides some examples for future applications in parasitology.

DNA evidence that Marshallagia marshalli Ransom, 1907 and M. occidentalis Ransom, 1907 (Nematoda: Ostertagiinae) from Svalbard reindeer are conspecific

The gastro-intestinal parasitic nematodes of ruminants Marshallagia marshalli and M. occidentalis are morphs of a single species according to indirect evidence. In this study, their taxonomic status and molecular identification were assessed more directly in isolates from the abomasal nematode community of Svalbard reindeer using genetic data. DNA sequences of the first and second internal transcribed spacers of nuclear ribosomal RNA genes were obtained from individual nematodes by the polymerase chain reaction (PCR). Both taxa contained virtually identical sequences of each ITS and shared most of the polymorphisms detected. A PCR assay based on ITS-2 sequences previously developed to identify M. marshalli and Ostertagia gruehneri, the second common species in this community, gave identical results for M. marshalli and M. occidentalis. Genetic data thus confirmed that M. marshalli and M. occidentalis are conspecific.

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.

Characterization of Otostrongylus circumlitus from Pacific harbor and northern elephant seals

Otostrongylus circumlitus (Railliet, 1899) from Pacific harbor seals (Phoca vitulina richardsi) and northern elephant seals (Mirounga angustirostris) were examined using morphological and molecular methods to determine whether northern elephant seals along the central California coast are infected by the same species of Otostrongylus as are Pacific harbor seals in the same area. Fixed nematodes were examined and measured using light microscopy. The polymerase chain reaction (PCR) was used to amplify and sequence the second internal transcribed spacer (ITS-2) and D3 expansion (26S) regions of ribosomal DNA of O. circumlitus from Pacific harbor and northern elephant seals. The ITS-2 region was also amplified from Parafilaroides sp. from the Pacific harbor seal, northern elephant seal, and California sea lion (Zalophus californianus) and used for restriction fragment length polymorphism (RFLP) analysis. Morphologically, it was not possible to distinguish O. circumlitus from Pacific harbor and northern elephant seals, and over a consensus length of 443 base pairs (bp) for ITS-2 and 321 bp for D3 the sequences of O. circumlitus from both hosts were identical. With the PCR-RFLP assay, it was possible to distinguish O. circumlitus from Parafilaroides sp. The results suggest that O. circumlitus is the same species in Pacific harbor and northern elephant seals, and molecular methods make it possible to distinguish this nematode from related nematodes.

Molecular and morphometric evidence for separate species of Uncinaria (Nematoda: Ancylostomatidae) in California sea lions and northern fur seals: hypothesis testing supplants verification

California sea lions (Zalophus californianus) and northern fur seals (Callorhinus ursinus) are each believed to host distinct hookworm species (Uncinaria spp.). However, a recent morphometric analysis suggested that a single species parasitizes multiple pinniped hosts, and that the observed differences are host-induced. To explore the systematics of these hookworms and test these competing hypotheses, we obtained nucleotide sequences of nuclear ribosomal DNA (D2/D3 28S, D18/D19 28S, and internal transcribed spacer [ITS] regions) from 20 individual hookworms parasitizing California sea lion and northern fur seal pups where their breeding grounds are sympatric. Five individuals from an allopatric population of California sea lions were also sampled for ITS-1 and D18/D19 28S sequences. The 28S D2/D3 sequences showed no diagnostic differences among hookworms sampled from individual sea lions and fur seals, whereas the 28S D18/D19 sequences had one derived (apomorphic) character demarcating hookworms from northern fur seals. ITS sequences were variable for 7 characters, with 4 derived (apomorphic) states in ITS-1 demarcating hookworms from California sea lions. Multivariate analysis of morphometric data also revealed significant differences between nematodes representing these 2 host-associated lineages. These results indicate that these hookworms represent 2 species that are not distributed indiscriminately between these host species, but instead exhibit host fidelity, evolving independently with each respective host species. This evolutionary approach to analyzing sequence data for species delimitation is contrasted with similarity-based methods that have been applied to numerous diagnostic studies of nematode parasites.

Comparison of ribosomal DNA sequences of Lamellodiscus spp. (monogenea, diplectanidae) parasitising Pagellus (sparidae, teleostei) in the North Mediterranean Sea: species divergence and coevolutionary interactions

We sequenced DNA fragments from four monogenean species of the genus Lamellodiscus and their three fish host species from the genus Pagellus in the North Mediterranean Sea, in order to estimate the molecular divergence and the coevolutionary interactions in this association. By comparing the ITS1 sequences of the parasites, we assessed their level of interspecific differences and tested the phylogenetic status of Lamellodiscus virgula and Lamellodiscus obeliae, formerly described as two different species. Moreover, we wanted to know if closely related parasites used closely related hosts, to investigate the coevolutionary interactions in this complex. Phylogenetic relationships among Lamellodiscus species were estimated with partial 18S ribosomal DNA sequences while mitochondrial cytochrome-b DNA sequences were used for their fish hosts. The ITS1 sequences appear to be highly variable among Lamellodiscus species, except L.virgula and L.obeliae, suggesting an old divergence time or a rapid molecular evolution within this genus. This fish-parasite association seems to exhibit coevolutionary interactions. L.virgula and L.obeliae are proposed to be a single species on the basis of their almost identical ITS1 sequences.

DNA evidence that Ostertagia gruehneri and Ostertagia arctica (Nematoda: ostertagiinae) in reindeer from Norway and Svalbard are conspecific

DNA sequences of ITS-1 and ITS-2 of rDNA were determined for 16 individual adult males each of Ostertagia gruehneri and Ostertagia arctica from Svalbard reindeer (Rangifer tarandus platyrhynchus) and Eurasian tundra reindeer (R. t. tarandus). Each ITS was virtually identical in O. gruehneri and O. arctica and the three mixed bases detected were shared by both species. Our results strongly suggest that O. gruehneri and O. arctica are dimorphic males of the same species.

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.

Characterisation of Ascaris from human and pig hosts by nuclear ribosomal DNA sequences

The sequences of the nuclear ribosomal DNA region spanning the first internal transcribed spacer, the 5.8S rRNA gene and the second internal transcribed spacer were determined for Ascaris samples from pigs and humans from different geographical regions. The sequences of the 5.8S gene and the second internal transcribed spacer were the same for all samples examined, whereas all Ascaris samples from humans had six (1.3%) nucleotide differences in the first internal transcribed spacer compared with those from pigs. These differences provided some support for the existence of separate species of Ascaris or population variation within this genus. Using a nucleotide difference within a site for the restriction enzyme HaeIII, a PCR-linked restriction fragment length polymorphism method was established which allowed the delineation of the Ascaris samples from pigs and humans used herein. Exploiting the sequence differences in the first internal transcribed spacer, a PCR-based single-strand conformation polymorphism method was established for future analysis of the genetic structure of pig and human Ascaris populations in sympatric and allopatric zones.