Distinguishing Oesophagostomum dentatum from Oesophagostomum quadrispinulatum developmental stages by a single-strand conformation polymorphism method

Identification of Chabertiidae (Nematoda, Strongylida) by PCR-RFLP based method: a new diagnostic tool for cross transmission investigation between domestic and wild ruminants in France

We describe a PCR-RFLP-based method that allows reliable identification of four species of nematode parasites presenting similar infective third-stage larvae (L3) with a flagelliform tail and more than 16 intestinal cells, commonly observed in gastrointestinal tract of ruminants in France. Molecular analysis of the second internal transcribed spacer (ITS2) of ribosomal DNA, considered as a specific marker for Strongylida, revealed four robust monophyletic clades corresponding to species Chabertia ovina, Oesophagostomum sikae, Oesophagostomum radiatum and Oesophagostomum venulosum. One restriction enzyme (DdeI) was used to digest this domain, and we observed four different and clear digestion patterns according to these species (adults or larvae). Hence, this new method is a good tool easy to use for veterinary laboratories to characterize the different species, and allows considering possible cross transmission between domestic and wild ruminants, especially cervids often incriminated as potential reservoir of parasites for cattle. Moreover, thanks to this new tool, necroscopic analyses could be substituted by coprological methods, a non-invasive approach.

Molecular diagnosis of infections and resistance in veterinary and human parasites

Since 1977, >2000 research papers described attempts to detect, identify and/or quantify parasites, or disease organisms carried by ecto-parasites, using DNA-based tests and 148 reviews of the topic were published. Despite this, only a few DNA-based tests for parasitic diseases are routinely available, and most of these are optional tests used occasionally in disease diagnosis. Malaria, trypanosomiasis, toxoplasmosis, leishmaniasis and cryptosporidiosis diagnosis may be assisted by DNA-based testing in some countries, but there are very few cases where the detection of veterinary parasites is assisted by DNA-based tests. The diagnoses of some bacterial (e.g. lyme disease) and viral diseases (e.g. tick borne encephalitis) which are transmitted by ecto-parasites more commonly use DNA-based tests, and research developing tests for these species makes up almost 20% of the literature. Other important uses of DNA-based tests are for epidemiological and risk assessment, quality control for food and water, forensic diagnosis and in parasite biology research. Some DNA-based tests for water-borne parasites, including Cryptosporidium and Giardia, are used in routine checks of water treatment, but forensic and food-testing applications have not been adopted in routine practice. Biological research, including epidemiological research, makes the widest use of DNA-based diagnostics, delivering enhanced understanding of parasites and guidelines for managing parasitic diseases. Despite the limited uptake of DNA-based tests to date, there is little doubt that they offer great potential to not only detect, identify and quantify parasites, but also to provide further information important for the implementation of parasite control strategies. For example, variant sequences within species of parasites and other organisms can be differentiated by tests in a manner similar to genetic testing in medicine or livestock breeding. If an association between DNA sequence and phenotype has been demonstrated, then qualities such as drug resistance, strain divergence, virulence, and origin of isolates could be inferred by DNA-based tests. No such tests are in clinical or commercial use in parasitology and few tests are available for other organisms. Why have DNA-based tests not had a bigger impact in veterinary and human medicine? To explore this question, technological, biological, economic and sociological factors must be considered. Additionally, a realistic expectation of research progress is needed. DNA-based tests could enhance parasite management in many ways, but patience, persistence and dedication will be needed to achieve this goal.

A multiplex PCR tool for the specific identification of Oesophagostomum spp. from pigs

Based on the sequences of the internal transcribed spacers (ITS-1 and ITS-2) of nuclear ribosomal deoxyribonucleic acid (DNA) of the porcine nodule worms Oesophagostomum dentatum and O. quadrispinulatum, a pair of specific primers (OdspF/OdspR2) for O. dentatum and a pair of specific primers (OqspF/OqspR) for O. quadrispinulatum were designed and used to develop a multiplex polymerase chain reaction (PCR) assay for the identification and differentiation of the two porcine nodule worms. This approach allowed the specific identification and differentiation of O. dentatum and O. quadrispinulatum, with no amplicons being amplified from heterogeneous DNA samples, and sequencing confirmed the identity of the sequences amplified. The minimum amount of DNA detectable using this multiplex PCR assay was 0.1 ng for both O. dentatum and O. quadrispinulatum. The identity of 53 porcine nodule worms collected from pigs from different geographical localities in mainland China was ascertained as O. dentatum or O. quadrispinulatum, respectively, by this multiplex PCR method. This multiplex PCR assay is useful for the simultaneous identification of eggs of O. dentatum and O. quadrispinulatum and should provide a useful tool for the diagnosis and molecular epidemiological investigation of Oesophagostomum spp. infection in pigs.

Characterization of Oesophagostomum spp. from pigs in China by PCR-based approaches using genetic markers in the internal transcribed spacers of ribosomal DNA

In the present study, samples of Oesophagostomum spp. collected from pigs from different geographical localities in mainland China were characterized genetically by polymerase chain reaction-linked single-strand conformation polymorphism (PCR-SSCP) and restriction fragment length polymorphism (PCR-RFLP) techniques using genetic markers in the internal transcribed spacers (ITS) of nuclear ribosomal DNA (rDNA). The second internal transcribed spacer (ITS-2) was amplified from 51 individual nodule worms by PCR, and the amplicons were analyzed by SSCP. With the exception of slight microheterogeneity, SSCP analyses displayed two distinct banding profiles that allowed the identification of all Oesophagostomum spp. samples examined into two groups, the first one represented O. dentatum, and the second one may represent O. quadrispinulatum. Then, the entire ITS was amplified from individual samples, and the amplicons were digested with restriction endonuclease Pst I. The results of RFLP analyses were consistent with that of SSCP. Sequence analysis of ITS rDNA supported the identification and differentiation of Chinese Oesophagostomum spp. samples into two species, namely, O. dentatum and O. quadrispinulatum. These PCR-based approaches provide useful complementary tools to traditional methods for the accurate identification of Oesophagostomum spp. (irrespective of developmental stage) and have implications for studying the ecology and population genetic structures of these parasites and for the prevention and control of the diseases they cause.

Molecular characterization of Thelazia lacrymalis (Nematoda, Spirurida) affecting equids: a tool for vector identification

Equine thelaziosis caused by the eyeworm Thelazia lacrymalis is a parasitic disease transmitted by muscid flies. Although equine thelaziosis is known to have worldwide distribution, information on the epidemiology and presence of the intermediate hosts of T. lacrymalis is lacking. In the present work, a PCR-RFLP based assay on the first and/or second internal transcribed spacer (ITS1 and ITS2) of ribosomal DNA was developed for the detection of T. lacrymalis DNA in its putative vector(s). The sensitivity of the technique was also assessed. The restriction patterns obtained readily differentiated T. lacrymalis from four species of Musca (Diptera, Muscidae) (i.e. Musca autumnalis, Musca domestica, Musca larvipara and Musca osiris), which are potential vectors of equine eyeworms. The molecular assay presented herein is a useful tool to identify the intermediate host(s) of T. lacrymalis in natural conditions and to study its/their ecology and epidemiology.

An electrophoretic tool for the genetic characterisation and delineation of lungworms

In the present study, PCR-based single-strand conformation polymorphism (SSCP) analysis of the second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA (rDNA) was applied to the genetic characterisation of Dictyocaulus from red deer from New Zealand and to its differentiation from species of lungworm from cattle and other hosts. Based on SSCP profiles, Dictyocaulus individuals from red deer from different geographical localities in New Zealand could be readily distinguished from those representing other lungworms examined, irrespective of low-level sequence variability in the ITS-2 (0.4-2.6%) detectable among individuals. The ITS-2 of Dictyocaulus from red deer differed in sequence by approximately 7-35% from congeners from other cervid hosts, demonstrating that this parasite is genetically distinct from other species of Dictyocaulus for which ITS-2 sequence data are presently available. The results emphasize the need for a large-scale molecular systematic study of Dictyocaulus specimens from various species of cervid and other ruminant hosts and the usefulness of mutation scanning for taxonomic, epidemiological and population genetic investigations.

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.

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.

Isolation, propagation and characterisation of Cryptosporidium

This review consists of 11 papers presented at the Consensus Conference on Cryptosporidium in Water (Parasitology Stream), held in Melbourne, Australia, from 5 to 6th October 1998. The conference was sponsored by the Water Services Association of Australia, the Australian Water and Wastewater Association, and the Collaborative Research Centre for Water Quality and Treatment. The papers summarise the advantages and disadvantages of various contemporary technologies applicable to parasite propagation and biochemical/molecular characterisation. Studies have detected distinct genetic differences between clinical isolates from humans and animals, and it is hoped that comprehensive documentation studies will facilitate the identification of environmental isolates in the not too distant future.

PCR-based technology in veterinary parasitology

DNA technology is having a major impact in many areas of veterinary parasitology. In particular, the polymerase chain reaction (PCR) has found broad applicability because its sensitivity permits enzymatic amplification of gene fragments from minute quantities of nucleic acids derived from limited amounts of parasite material. This paper discusses some recent applications of PCR-based methods to parasites and highlights their usefulness or potential for those of veterinary importance. The focus is on PCR tools for the accurate identification of parasites and their genetic characterisation, the diagnosis of infections, the isolation and characterisation of expressed genes, the detection of anthelmintic resistance, and mutation scanning approaches for the high resolution analysis of PCR products.