Use of genomic DNA restriction fragment length differences to identify nematode species

Current advances in the identification of plant nematode diseases: From lab assays to in-field diagnostics

Plant parasitic nematodes (PPNs) cause an important class of diseases that occur in almost all types of crops, seriously affecting yield and quality and causing great economic losses. Accurate and rapid diagnosis of nematodes is the basis for their control. PPNs often have interspecific overlays and large intraspecific variations in morphology, therefore identification is difficult based on morphological characters alone. Instead, molecular approaches have been developed to complement morphology-based approaches and/or avoid these issues with various degrees of achievement. A large number of PPNs species have been successfully detected by biochemical and molecular techniques. Newly developed isothermal amplification technologies and remote sensing methods have been recently introduced to diagnose PPNs directly in the field. These methods have been useful because they are fast, accurate, and cost-effective, but the use of integrative diagnosis, which combines remote sensing and molecular methods, is more appropriate in the field. In this paper, we review the latest research advances and the status of diagnostic approaches and techniques for PPNs, with the goal of improving PPNs identification and detection.

Trichinella species and genotypes

Trichinella spiralis has historically been deemed "the pig parasite" owing to its initial classification within a monospecific genus. However, in recent years, the genus has expanded to include 10 distinct species and at least 3 different genotypes whose taxonomic status remains unstipulated. In contrast to T. spiralis, however, most of these sylvatic species and genotypes do not infect pigs well. Inasmuch as morphological characters cannot be used to define species within this genus, earlier classifications were based upon host and geographical ranges, biological characters, and the presence or absence of a collagen capsule that surrounds the muscle stage larvae. Later, isoenzymes, DNA gel fragmentation patterns and DNA probes were used to help in identification and classification. Today, amidst the "-omics" revolution, new molecular and biochemical-based methodologies have improved detection, differentiation and characterization at all levels including worm populations. These efforts have discernably expanded immunological, epidemiological, and genetic studies resulting in better hypotheses on the evolution of the genus, and on global events, transmission cycles, host associations, and biogeographical histories that contributed to its cosmopolitan distribution. Reviews of this sort are best begun with a background on the genus; however, efforts will divert to the most recent knowledge available on the taxonomy, phylogeny, epidemiology and biochemistry that define this genus in the 21st century.

Quantification of Paratrichodorus allius in DNA extracted from soil using TaqMan Probe and SYBR Green real-time PCR assays

The ectoparasitic stubby root nematode,Paratrichodorus allius, transmits tobacco rattle virus, which causes corky ringspot disease resulting in significant economic losses in the potato industry. A diagnostic method for direct quantification ofP. alliusfrom soil DNA using TaqMan probe and SYBR Green real-time PCR assays was developed to assist the potato industry in management of this important vector. Specificity of primers/probe designed from the internal transcribed spacer of ribosomal DNA ofP. alliuswas demonstrated byin silicoanalysis and experimental PCR tests with no cross reactions using non-target nematode species and nematode communities. The SYBR Green method was more sensitive than the TaqMan probe method during detection using serial diluted DNA templates. Standard curves were generated from serial dilutions of DNA extracted from autoclaved soil with artificially inoculatedP. alliusindividuals and were validated by high correlations between the numbers of target nematodes quantified by the assays and added to the soil. Moreover, the numbers ofP. alliusdetermined by the real-time PCR assays and estimated by the microscopic method in 17 field soil samples presented positive correlation relationships (). Although the quantification using TaqMan probe overestimated the target nematodes compared to using SYBR Green in eight out of ten field soil samples, results of the two methods correlated well (). This is the first report ofP. alliusquantification from soil DNA extracts using real-time PCR, providing a rapid and sensitive diagnostic method obviating time-consuming manual nematode extraction from soil and microscopic identification and quantification.

Repetitive DNA and hybridization patterns demonstrate extensive variability between the sibling species Globodera rostochiensis and G. pallida

A method is described for the isolation of high molecular weight DNA from females of potato cyst nematodes. Restriction enzyme analyses of repetitive DNA revealed 30 bands specific for Globodera rostochiensis and 8 bands specific for G. pallida. None of the repetitive DNA bands resolved was common to both species. Hybridization patterns, obtained with a DrosophilaβJ-tubulin probe, revealed 4 common bands, 3 bands specific for G. rostochiensis and 12 bands specific for G. pallida.

Differentiation of isolates in the genus Steinernema (Nematoda: Steinernematidae).by random amplified polymorphic DNA fragments and morphological characters

We combined polymerase chain reaction (PCR) amplification of DNA sequences and important morphological characters as a technique to differentiate nematode isolates in the genus Steinernema. Five decamer oligonucleotide primers were used to generate random amplified polymorphic DNA (RAPD) fragments from 11 nematode isolates. The primers generated 8–12 fragments, ranging from 220 to 1300 bp in size. Reproducible amplified DNA fragments of 11 isolates showed obviously inter- or intra-specific polymorphisms, enabling us to differentiate easily the nematode species and isolates. Combining RAPD–PCR fragments with the examination of morphological characters of infective juveniles and 1st-generation males, we identified isolate OH1S, collected from Newport, Oregon, as S.feltiae; isolate OS21, collected from Grants Pass, Oregon, belonged to a previously undescribed species. Our study may provide a rapid and reliable method for the identification of Steinernema nematodes.

Origin, distribution and 3D-modeling of Gr-EXPB1, an expansin from the potato cyst nematode Globodera rostochiensis

Southern analysis showed that Gr-EXPB1, a functional expansin from the potato cyst nematode Globodera rostochiensis, is member of a multigene family, and EST data suggest expansins to be present in other plant parasitic nematodes as well. Homology modeling predicted that Gr-EXPB1 domain 1 (D1) has a flat beta-barrel structure with surface-exposed aromatic rings, whereas the 3D structure of Gr-EXPB1-D2 was remarkably similar to plant expansins. Gr-EXPB1 shows highest sequence similarity to two extracellular proteins from saprophytic soil-inhabiting Actinobacteria, and includes a bacterial type II carbohydrate-binding module. These results support the hypothesis that a number of pathogenicity factors of cyst nematodes is of procaryotic origin and were acquired by horizontal gene transfer.

Genetic variability of the human filarial parasite, Wuchereria bancrofti in South India

The genetic variability of the lymphatic filarial parasite Wuchereria bancrofti, from three localities (one urban and two rural areas) in southern India, endemic for filariasis was studied using random amplified polymorphic DNA (RAPD) markers. The RAPD profiles were generated for 21 parasite populations (7 populations from each area), using a 10-mer random primer. The analysis of profiles indicated the existence of considerable genetic variability among parasite populations. The Nei's gene diversity between the individual populations in the 2 areas (one urban and another rural) was comparatively greater (0.3372+/-0.1462 & 0.2830+/-0.1764) than that of populations in another village (0.0490+/-0.1373). The greater genetic diversity among the former areas may be due to human migration, endemicity for long time and drug (diethyl-carbamazine citrate) pressure unlike the populations of latter village where the filariasis is relatively a recent introduction and which was never under active chemotherapy. The Nei's genetic distance was estimated and the phylogenetic tree was constructed using 'UPGMA'. These analyses indicated the prevalence of at least two genetically distinct clusters, among the populations studied, their maximum genetic distance being 0.2444. The finding of two genetic 'variants' of W. bancrofti, in the present study, may have important implications in filariasis epidemiology and control/elimination programmes.

Evaluation of PCR, IEF and ELISA techniques for the detection and identification of potato cyst nematodes from field soil samples in England and Wales

Effective management of potato cyst nematodes (PCNs) requires simple, rapid and accurate identification and quantification of field populations. Soil samples from a survey of 484 fields in potato rotations in England and Wales were used to compare the identification and quantification of PCNs using IEF, PCR, ELISA and bait plant tests. The cyst counts and bait plant test revealed that 64.3% of field samples contained PCNs. Bait plant tests increased the detection rate of PCNs in field samples by 4-6.4%. This means that some infestations are cryptic and would not normally be detected by standard counts. IEF, PCR and ELISA methods distinguished between Globodera rostochiensis and G pallida and were able to register mixed populations; however they were not in full agreement. All methods suggested that G pallida is the dominant species in the field samples tested. The PCR results indicated that 66% of field samples contained pure G pallida, 8% contained pure G rostochiensis and 26% contained mixtures of the two species. Estimates of the relative process times taken per sample in the PCR, IEF and ELISA techniques are given.

Molecular and biochemical methods for parasite differentiation within the genus Trichinella

Delineation of the genus Trichinella into a more complex group of parasites has substantially motivated investigators to better identify and characterize the species and genotypes that form the basis of their investigations. Because of the cosmopolitan geographical distribution and broad host range that typify this genus, assigning unique biological, immunological and biochemical characters to each species and genotype has been essential for researchers to further advance this field. Numerous groups have developed simple methods to differentiate the genotypes, and by so doing, have generated diagnostic keys that accurately reflect the distinct differences among parasites of this group. Throughout the years, many methods have been used to accomplish this task, beginning with isoenzyme analyses and the use of repetitive DNA probes, to employing the polymerase chain reaction (PCR) and more state-of-the-art technologies. This review article summarizes the development of these methods with emphasis on molecular techniques and the ultimate goal of providing a simple, rapid and reproducible test to differentiate Trichinella parasites at the highest level of sensitivity, i.e. single parasite.

Control of insect pests with entomopathogenic nematodes: the impact of molecular biology and phylogenetic reconstruction

Entomopathogenic nematodes are excellent biological control agents. Utilization of these nematodes is developing rapidly with almost a doubling of newly described species in the past five years. Advances in molecular biology and phylogenetic reconstruction have revolutionized understanding of population structure, identification, genetic improvement, systematics, and the symbiosis between entomopathogenic nematodes and their bacteria. Population structure provides the most fundamental information for reliable identification of species and unique genetic variants. Such information could be further assessed for nematode potential as biological control agents. Phylogenetic reconstruction is an important approach for understanding multitrophic interactions among entomopathogenic nematodes, symbiotic bacteria, and their insect hosts. Phylogenetic reconstruction is also important for the development of a natural and stable type of systematics, which can provide guidelines for selecting appropriate entomopathogenic nematode species for particular biological control programs.

Cloning of a trans-spliced glyceraldehyde-3-phosphate-dehydrogenase gene from the potato cyst nematode Globodera rostochiensis and expression of its putative promoter region in Caenorhabditis elegans

Reverse genetics to determine the relative importance of individual pathogenicity factors of the potato cyst nematode Globodera rostochiensis depends, apart from an efficient transformation protocol for this obligatory plant parasite, on the availability of an efficient promoter. PCR-based cloning was used to isolate a cDNA encoding glyceraldehyde-3-phosphate-dehydrogenase (GAPDH, a crucial enzyme in glycolysis and gluconeogenesis; this gene was designated gpd) and its 5'-flanking region. The cDNA includes 1047 nucleotides encoding an open reading frame that shows high homology with GAPDHs from Caenorhabditis elegans and other species. Analysis of the 745 bp 5'-flanking region of the gpd gene showed no homology with a similar region in C. elegans. In this region several eukaryotic promoter elements are present. 5' Rapid amplification of cDNA ends revealed this gene was trans-spliced with a SL1 spliced leader. The 5'-flanking region of the gpd gene was fused to green fluorescent protein reporter gene and microinjected into the gonads of C. elegans. Green fluorescent protein expression, under the transcriptional control of the 5'-flanking region of gpd, was mainly observed in body wall muscles of transgenic animals. This putative promoter region of GAPDH could be a valuable tool to drive gene expression in transgenic G. rostochiensis and other related plant-parasitic nematode species.

Evidence of two genetic entities in Bothriocephalus funiculus (Cestoda) detected by arbitrary-primer polymerase chain reaction random amplified polymorphic DNA fingerprinting

The genetic diversity of two samples of Cestoda (Bothriocephalus funiculus, Renaud and Gabrion, 1984) parasitizing two sympatric teleostean species was assessed using random amplified polymorphic DNA (RAPD). A total of 72 Bothriocephalus were analyzed individually, and electrophoretic analysis of the amplification products of 65 primers among the 68 tested revealed monomorphic patterns, reflecting the close genetic relatedness within and between the parasites of the two samples. However, 3 primers showed polymorphic patterns at 6 RAPD sites. Analysis of the distribution of these genomic fragments, assuming random mating, showed strong linkage disequilibria (only 8 genetic combinations were observed among the 32 expected). Two genetic entities displaying a high degree of host specificity were evidenced within our two samples of funiculus. This powerful molecular technique can be used as a diagnostic tool in studies concerning the biodiversity of related genetic entities and could have broad applications in parasitology.

Discrimination between Gyrodactylus salaris, G. derjavini and G. truttae (Platyhelminthes: Monogenea) using restriction fragment length polymorphisms and an oligonucleotide probe within the small subunit ribosomal RNA gene

The small subunit ribosomal RNA (srRNA) gene was amplified from Gyrodactylus salaris using the polymerase chain reaction (PCR), cloned, and the complete gene sequence of 1966 bp determined. The V4 region of the srRNA gene was identified and amplified from single specimens of G. salaris, G. derjavini and G. truttae. Comparison of the V4 sequences from these three species revealed sequence differences from which restriction fragment length polymorphisms (RFLPs) were predicted and an oligonucleotide probe (GsV4) specific to G. salaris designed. Digestion of the amplified V4 region of the srRNA gene with Hae III and either Alw I, BstY I, Dde I or Mbo I provided a means of discriminating between G. salaris, G. derjavini and G. truttae. The GsV4 probe was used to detect the srRNA gene from G. salaris in Southern and dot blots of the amplified V4 region.

Intraspecific variation of Taenia taeniaeformis as determined by various criteria

The intraspecific variation of four laboratory-reared isolates of Taenia taeniaformis the SRN and KRN isolates from Norway rats, Rattus norvegicus, captured in Japan and Malaysia, respectively; the BMM isolated from a house mouse, Mus musculus, captured in Belgium; and the ACR isolate from a gray red-backed vole, Clethrionomys rufocanus bedfordiae, captured in Japan was examined by various criteria. Eggs of each of the four isolates were orally inoculated into several species of intermediate host. They were most infective to the rodent species from which the original metacestode of each isolate had been isolated in the field, and only the ACR isolate was infective to the gray red-backed vole. Although little difference was found between the SRN, KRN, and BMM isolates by the other criteria, including the morphology of rostellar hooks, the protein composition of the metacestode, and restriction endonuclease analysis of DNA, the ACR isolate was clearly different from the others. It was considered that the ACR isolate was independent as a strain distinct from the other three isolates.

The differentiation of parasitic nematodes using random amplified polymorphic DNA

DNA from species and races of plant parasitic nematodes (Meloidogyne, Globodera and Heterodera) and a human parasitic nematode (Trichinella) were subjected to polymerase chain reaction amplification using one arbitrary primer (M-10). This technique results in relatively simple DNA profiles that include polymorphic markers known as random amplified polymorphic DNA (RAPDs). The RAPD profiles of the plant nematode species of Meloidogyne made possible the identification of M. incognita and M. hapla, but no differences were found between the patterns of M. javanica, M. arenaria and M. graminicola. Moreover, the four races of M. incognita were indistinguishable by this primer. In contrast, when races of the plant nematode Globodera rostochiensis (Ro1 and Ro2/3) were studied under the same RAPDs conditions, a race specific profile allows these two most devastating races to be differentiated. When DNAs of eight Trichinella isolates were subjected to RAPD studies, four different patterns were identified, corresponding to the four Trichinella clusters previously defined by isozyme polymorphism.

Ribosomal DNA sequences discriminate among toxic and non-toxic Pseudonitzschia species

Cultured isolates of Pseudonitzschia australis Frenguelli, P. delicatissima (Cleve) Heiden, P. americana (Hasle) Fryxell, P. pungens (Grunow) Hasle, and P. pungens f. multiseries (Hasle) Hasle from Monterey Bay, California, were compared on the basis of their large-subunit ribosomal RNA gene (LsrDNA). Pseudonitzschia australis, P. pungens f. multiseries, and P. delicatissima were previously shown to produce the neurotoxin domoic acid; the remaining isolates are considered non-toxic. For each isolate approximately 800 base pairs of LsrDNA, encompassing both evolutionarily conserved and evolutionarily variable regions of the molecule, were amplified using the polymerase chain reaction (PCR) and sequenced. Phylogenetic trees generated by parsimony analysis of aligned sequences afford a preliminary view of the organisms genetic relationships. Species defined by morphological criteria are also distinguishable by LsrDNA sequence. Organisms known or suspected to produce domoic acid cluster at different termini on the phylogenetic tree. Two genetically distinct strains of P. australis and P. pungens were identified. Development of a restriction fragment length polymorphism (RFLP) assay of the LsrDNA is described. The RFLP assay discriminates each species, including distinguished strains of P. australis and P. pungens. The restriction test provides a rapid and convenient method for screening isolates' LsrDNA, facilitating further tests of the apparent positive correlation between Pseudonitzschia species' ribosomal gene signatures, morphology, and capacity to produce domoic acid.

Differentiation of Trichinella isolates by polymerase chain reaction

Oligonucleotide primers were synthesized for the polymerase-chain-reaction amplification of target DNA from two sequences of Trichinella spiralis. Six strains belonging to T. spiralis, T. nativa, T. britovi, T. pseudospiralis, and T. nelsoni were tested. Amplification products were obtained with T. spiralis, T. britovi, and T. nelsoni DNA from a 53-kDa antigen cDNA sequence and with T. spiralis and T. nelsoni DNA from a 1.6-kb repetitive DNA sequence. Differences in the length of the amplification products obtained from the repetitive sequence would enable a differentiation between T. spiralis and T. nelsoni, suggesting that the 1.6 kb repetitive DNA sequence would not be specific for T. spiralis. No amplification was detected for T. nativa or T. pseudospiralis DNA from the two sequences and for T. britovi DNA from the 1.6-kb repetitive DNA sequence.

Isoenzyme studies in one Brazilian and two Venezuelan strains of Schistosoma mansoni

1. Enzyme polymorphism, analyzed by starch gel electrophoresis, was found to be zero for acid phosphatase, phosphoglucomutase, phosphoglucose isomerase, glucose 6-phosphate dehydrogenase, lactate dehydrogenase, malate dehydrogenase and malic enzyme, in one Brazilian and two Venezuelan strains of Schistosoma mansoni. 2. All loci studied were monomorphic within strains, but the isoenzymic patterns were, however, different among the strains. 3. Results suggest a drastic loss of the genetic variability usually found in natural populations.

Molecular diagnostics for plant nematodes

Plant parasitic nematodes are a source of considerable economic loss to arable farmers. However, the cost of nematode control is also escalating, both in financial and environmental terms. Nevertheless, there are alternative methods of control in current use. As Tom Powers emphasizes in this article, to be effective, crop rotation and the use of resistant strains of host plant need to be accompanied by sensitive methods for parasite strain identification. Morphologically, there is little by which to separate nematode pothotypes and consequently technologies are being introduced to tackle these problems at the level of their genes.

A repetitive DNA probe specific for a North American sylvatic genotype of Trichinella

A partial genomic DNA library constructed in pUC 13 using DNA from a sylvatic isolate of Trichinella spiralis (T. spiralis T5) was differentially screened with radiolabeled homologous genomic DNA and with DNA from T. spiralis T1. One clone was identified and designated pUPB-3.7 which, by slot blot and Southern blot analyses, reacted specifically with T. spiralis T5 DNA and did not cross-react with DNA from any other T. spiralis genotype. The 482-bp repetitive sequence which is 70% rich in A and T residues, comprises at least 2.7% of the parasite genome and can detect as little as 0.4 ng of DNA. When used to assess the prevalence of T. spiralis T5 in Indiana wildlife, DNA from 19 of 20 independently obtained sylvatic isolates reacted positively with the pUPB-3.7 probe indicating that within this geographical locality, T. spiralis T5 is the predominating genotype in wild mammals.

A species-specific oligonucleotide DNA probe for the identification of Meloidogyne incognita

A genomic library of Meloidogyne incognita Race 1 has been prepared in the bacteriophage lambda gt10 and screened for specific DNA sequences by hybridization with radio-isotope labelled total genomic DNA from a number of Meloidogyne species. One clone isolated (MR1 #15), although not totally species specific, clearly showed preferential hybridization to M. incognita. Following subcloning and sequencing of the 255 bp insert, four stretches of the sequence corresponding to oligonucleotides of approximately equal length (approximately 70 bp) were synthesized and examined for specificity. One of them, MR1 #15.2, showed the necessary specificity to be used as a diagnostic tool.

DNA probes for the detection of Babesia caballi

A genomic library of Babesia caballi DNA was constructed in the plasmid vector pUC13. The specificity of the clones for B. caballi was established by the lack of hybridization to Babesia equi, Babesia bovis, Babesia bigemina and equine DNA. Two probes, pBC11 and pBC191, were isolated that could detect 0.25 ng and 0.125 ng of B. caballi DNA, corresponding to a parasitaemia of 0.12% and 0.06% respectively. pBC191 could detect B. caballi parasites in the blood of an experimentally infected horse as well as in naturally infected horses.

The isolation of nucleic acid from nematodes requires an understanding of the parasite and its cuticular structure

As parasitology increasingly becomes the domain of molecular biologists, it is important to keep in mind that a fundamental understanding of the whole parasite, its structure and behaviour can help to solve complex problems of molecular biology. Hugh Dawkins and Terence Spencer discuss the preparation of DNA from filaform larvae of Trichostrongylus colubriformis and Ostertagia circumcincta and how a detailed knowledge of the morphology and life cycle of each parasite helps in this process.

Trichinella spiralis: genetic evidence for synanthropic subspecies in sylvatic hosts

Isolates of the nematode genus Trichinella from sylvatic hosts differ in their potential to reproduce in domestic swine. The structure of the genomic DNA from 13 sylvatic isolates from North America and 5 pig isolates, 4 from North America and 1 from Asia, was examined and correlated with the infectivity of the isolate for domestic pigs. DNA restriction fragment length differences, identified by ethidium bromide staining and by hybridization with 32P-labeled ribosomal RNA, served as molecular markers to classify each isolate. All 5 pig isolates and 8 of 13 sylvatic isolates had a high infectivity and reproductive capacity in pigs. All isolates that were highly infectious for pigs regardless of host origin had similar DNA characteristics and were classified operationally as T. spiralis spiralis (pig) and those of the second group as T. spiralis ssp. A DNA clone of repetitive DNA from T. s. spiralis, pBP2, was selected from a library of genomic DNA in plasmid pUC8. When used as a probe, pBP2 hybridized only to the DNA of T. s. spiralis isolates, thus making it a useful diagnostic reagent to predict whether new isolates are highly infectious for pigs (i.e., T. s. spiralis). These results show that T. s. spiralis occurs in wild mammals and this should be considered a serious obstacle to efforts to eradicate trichinellosis from domestic swine.

Repetitive DNA as a tool for the identification and comparison of nematode variants: application to Trichinella isolates

DNA prepared from four isolates of Trichinella was compared by genomic DNA cross-hybridisation, by electrophoresis following restriction endonuclease digestion and by hybridisation studies using a cloned repetitive DNA sequence from T. spiralis. The DNA from T. spiralis, T. nelsoni and T. pseudospiralis isolates was distinct and the interrelationships of these isolates were inferred. In contrast to previous work on T. nativa and T. spiralis, our work suggests that these two isolates are very similar.

Phylogeny of helminths determined by rRNA sequence comparison

The nucleotide sequence of the 5' ends of the 28S-like rRNA molecules of five species of helminths was determined directly, using a variation on the dideoxynucleotide chain-termination method which requires only 10 micrograms of total cellular RNA for analysis. Nucleotide sequence comparisons over 208 bases allowed the phylogeny of these organisms to be determined. The data show that the rRNA sequence of Nematospiroides dubius, a nematode, is as divergent from that of two platyhelminths, Hymenolepis diminuta and Schistosoma mansoni, as it is from the rRNA sequence of the two nematodes Onchocerca gibsoni and Brugia pahangi. The latter two appear to be very closely related, whereas the two platyhelminths are more distant from each other. The study demonstrates the usefulness and generality of rRNA sequencing for the systematic phylogenetic classification of parasitic organisms whose tissues are only available in relatively small amounts.

The application of recombinant DNA technology to problems of helminth identification

During the past decade, enormous technological developments have occurred in biology that have led to significant and revolutionary advances. New techniques of DNA cloning, restriction-enzyme analyses and nucleotide sequencing are providing a mass of data concerning the genomes of a wide variety of organisms. Such insights are having a great impact upon many areas of biological investigation, and would seem to be of considerable potential value for studies of taxonomy and population biology. The application of these new approaches to the characterization and identification of parasitic helminths has only recently begun, but they promise to become powerful additional tools for this purpose. Better methods of characterization are required for more precise definition of the parasites of man and domestic animals and for determining vectors and intermediate hosts as well as possible animal reservoir hosts. Moreover, a greater understanding of the genetic diversity of parasitic organisms is required since many helminths, which are morphologically similar, show marked differences in epidemiologically significant factors such as infectivity, pathogenicity, immunogenicity and drug sensitivity.

Identification of the Echinococcus (hydatid disease) organisms using cloned DNA markers

Cloned DNA fragments of the ribosomal RNA gene of Schistosoma mansoni hybridise strongly to Echinococcus DNA following restriction endonuclease and Southern transfer analysis. Individuals within a strain of E. granulosus exhibit identical patterns of hybridisation. However, the hybridisation patterns show significant differences between E. granulosus and E. multilocularis, and between the horse and sheep strains of E. granulosus. This technique represents a powerful, additional method for the identification and characterisation of new isolates of E. granulosus and E. multilocularis.