Microsatellite genotyping supports the hypothesis that Teladorsagia davtiani and Teladorsagia trifurcata are morphotypes of Teladorsagia circumcincta

Advances in diagnosis of gastrointestinal nematodes in livestock and companion animals

Diagnosis of gastrointestinal nematodes in livestock and companion animals has been neglected for years and there has been an historical underinvestment in the development and improvement of diagnostic tools, undermining the undoubted utility of surveillance and control programmes. However, a new impetus by the scientific community and the quickening pace of technological innovations, are promoting a renaissance of interest in developing diagnostic capacity for nematode infections in veterinary parasitology. A cross-cutting priority for diagnostic tools is the development of pen-side tests and associated decision support tools that rapidly inform on the levels of infection and morbidity. This includes development of scalable, parasite detection using artificial intelligence for automated counting of parasitic elements and research towards establishing biomarkers using innovative molecular and proteomic methods. The aim of this review is to assess the state-of-the-art in the diagnosis of helminth infections in livestock and companion animals and presents the current advances of diagnostic methods for intestinal parasites harnessing (i) automated methods for copromicroscopy based on artificial intelligence, (ii) immunodiagnosis, and (iii) molecular- and proteome-based approaches. Regardless of the method used, multiple factors need to be considered before diagnostics test results can be interpreted in terms of control decisions. Guidelines on how to apply diagnostics and how to interpret test results in different animal species are increasingly requested and some were recently made available in veterinary parasitology for the different domestic species.

Genotypic characterisation of monepantel resistance in historical and newly derived field strains of Teladorsagia circumcincta

Recent reports of monepantel (MPTL) resistance in UK field isolates of Teladorsagia circumcincta has highlighted the need for a better understanding of the mechanism of MPTL-resistance in order to preserve its anthelmintic efficacy in this economically important species. Nine discrete populations of T. circumcincta were genotypically characterised; three MPTL-susceptible isolates, three experimentally selected MPTL-resistant strains and three field derived populations. Full-length Tci-mptl-1 gene sequences were generated and comparisons between the MPTL-susceptible isolates, MPTL-resistant strains and one field isolate, showed that different putative MPTL-resistance conferring mutations were present in different resistant isolates. Truncated forms of the Tci-mptl-1 gene were also observed. The genetic variability of individual larvae, within and between populations, was examined using microsatellite analyses at 10 'neutral' loci (presumed to be unaffected by MPTL). Results confirmed that there was little background genetic variation between the populations, global FST <0.038. Polymorphisms present in exons 7 and 8 of Tci-mptl-1 enabled genotyping of individual larvae. A reduction in the number of genotypes was observed in all MPTL-resistant strains compared to the MPTL-susceptible strains that they were derived from, suggesting there was purifying selection at Tci-mptl-1 as a result of MPTL-treatment. The potential link between benzimidazole (BZ)-resistance and MPTL-resistance was examined by screening individual larvae for the presence of three SNPs associated with BZ-resistance in the β-tubulin isotype-1 gene. The majority of larvae were BZ-susceptible homozygotes at positions 167 and 198. Increased heterozygosity at position 200 was observed in the MPTL-resistant strains compared to their respective MPTL-susceptible population. There was no decrease in the occurrence of BZ-resistant genotypes in larvae from each population. These differences, in light of the purifying selection at this locus in all MPTL-resistant isolates, suggests that Tci-mptl-1 confers MPTL-resistance in T. circumcincta, as in Haemonchus contortus, but that different mutations in Tci-mptl-1 can confer resistance in different populations.

Infracommunity crowding as an individual measure of interactive-isolationist degree of parasite communities: disclosing the effects of extrinsic and host factors

Background

Interactions between parasite species within a host play a fundamental role in shaping parasite communities that have been classified within a continuum between interactive and isolationist. Interactive communities are principally structured by interactions between parasite species, while isolationist communities are structured by processes independent of the presence of other parasite species. Assessing whether, and to what extent, parasite communities exist along this continuum has been challenging due to a lack of an index that quantifies the degree of interactivity. Moreover, the absence of an index at the individual host level has made it unfeasible to identify host and extrinsic factors that may influence the degree of interactivity of a parasite community.

Methods

Here we propose an infracommunity crowding index that can reflect the degree of interactivity of a parasite community within each individual. This index quantifies the mean number of parasites that the average parasite within a community is exposed to, including the different aspects of parasite communities important in determining the level of interactivity, i.e. total abundance, species richness and evenness. We applied this analytical approach to the abomasal parasite communities of three alpine ruminant species that are traditionally viewed as isolationist.

Results

The application of our index to abomasal parasite communities shows that the majority of parasites live in highly crowded communities, suggesting that these host species harbour interactive parasite communities. In addition, the infracommunity crowding was highly variable and influenced by the host species, as well as by the timing of sampling and host age and sex.

Conclusions

Despite increasing evidence on the influence of interactions between parasite species in shaping infections, an analytical measure to quantify the degree of interactivity of parasite communities is lacking. Here we present a new analytical approach which, when applied to parasite communities, appears to be sensitive to both extrinsic and host factors, highlighting that the degree of interactivity is not a static and specific feature of host species, but rather a dynamical process that keeps evolving during host’s life. The new index provides opportunities for further investigations aimed at revealing the determinants of parasite interactivity.

Insight into species diversity of the Trichostrongylidae Leiper, 1912 (Nematoda: Strongylida) in ruminants

This paper focuses on the species diversity among the Trichostrongylidae Leiper, 1912 (Nematoda: Strongylida), and complexity of the family systematics. Polymorphism (subfamilies: Ostertagiinae, Cooperiinae and Haemonchinae), the presence of cryptic species (genus: Teladorsagia) and hybridization (genera: Cooperia, Haemonchus and Ostertagia) are presented and discussed, considering both morphological and molecular evidence. Some of these phenomena are common, nevertheless not sufficiently understood, which indicates the need for expanding the current state of knowledge thereof. Within the Trichostrongylidae, species distinction supported merely by morphological features is difficult, and requires confirmation by means of molecular methods. The parasitic nematode taxonomy is complicated mainly by the genus Teladorsagia, but complexity may also be expected among other Ostertagiinae (e.g. in the genera Ostertagia and Marshallagia). The data presented here show that the members of the Trichostrongylidae can significantly complicate unambiguous species identification. Hence, it is essential to consider the phenomena mentioned, to gather valid and comparable data on the biodiversity of this family.

Species discrimination in the subfamily Ostertagiinae of Northern China: assessment of DNA barcode in a taxonomically challenging group

Gastrointestinal nematodes within the subfamily Ostertagiinae (Teladorsagia, Ostertagia, and Marshallagia et al.) are among the most common infections of domesticated livestock. These parasites are of particular interest, as many of the species within this group are of economic importance worldwide. Traditionally, nematode species designations have been based on morphological criteria. However, this group possesses poorly defined species. There is an urgent need to develop a reliable technique that can distinguish species of Ostertagiinae. DNA barcoding has been proved to be a powerful tool to identify species of birds, mammals, and arthropods, but this technique has not yet been examined for identifying species of Ostertagiinae. In this study, a total of 138 mitochondrial DNA (mtDNA) cytochrome c oxidase subunit I (COI) sequences from individuals representing 11 species of Ostertagiinae were acquired by PCR for the first time. The specimens were collected from pastoral area of northern China. Genetic divergence analyses showed that mean interspecific Kimura two-parameter distances of COI (13.61 %) were about four times higher than the mean value of the intraspecific divergence (3.69 %). Then, the performance of the COI to identify species of Ostertagiinae was evaluated by identification success rates using nearest neighbor (NN) and BLASTn. The results indicated that the rates of correct sequence identification for COI were high (>80 %) when using the NN and BLASTn methods. Besides, the deep lineage divergences are detected in Teladorsagia circumcincta. Meanwhile, the analyses also detected no genetic differentiation between some species such as Ostertagia hahurica and Ostertagia buriatica. These results indicate that the traditional status of species within Ostertagiinae should be closely examined based on the molecular data.

Unravelling parasitic nematode natural history using population genetics

The health and economic importance of parasitic nematodes cannot be overstated. Moreover, they offer a complex and diverse array of life strategies, raising a multitude of evolutionary questions. Researchers are applying population genetics to parasitic nematodes in order to disentangle some aspects of their life strategies, improve our knowledge about disease epidemiology, and design control strategies. However, population genetics studies of nematodes have been constrained due to the difficulty in sampling nematodes and developing molecular markers. In this context, new computational and sequencing technologies represent promising tools to investigate population genomics of parasitic, non-model, nematode species in an epidemiological context.

Testing local-scale panmixia provides insights into the cryptic ecology, evolution, and epidemiology of metazoan animal parasites

When every individual has an equal chance of mating with other individuals, the population is classified as panmictic. Amongst metazoan parasites of animals, local-scale panmixia can be disrupted due to not only non-random mating, but also non-random transmission among individual hosts of a single host population or non-random transmission among sympatric host species. Population genetics theory and analyses can be used to test the null hypothesis of panmixia and thus, allow one to draw inferences about parasite population dynamics that are difficult to observe directly. We provide an outline that addresses 3 tiered questions when testing parasite panmixia on local scales: is there greater than 1 parasite population/species, is there genetic subdivision amongst infrapopulations within a host population, and is there asexual reproduction or a non-random mating system? In this review, we highlight the evolutionary significance of non-panmixia on local scales and the genetic patterns that have been used to identify the different factors that may cause or explain deviations from panmixia on a local scale. We also discuss how tests of local-scale panmixia can provide a means to infer parasite population dynamics and epidemiology of medically relevant parasites.

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.

Sex ratio and morphological polymorphism in an isolated, endemicTeladorsagia circumcinctapopulation

Teladorsagia circumcinctais a polygamous nematode that exhibits morphological polymorphism. Sex ratio is typically female biased and the male nematodes occur in association with the genetically similar, minor morphotypesTeladorsagia davtianiandTeladorsagia trifurcata. In experimental infections, sex ratio (proportion male) and the proportion of minor male morphs observed have been shown to be influenced by both host and nematode-related factors. As similar investigations from natural systems are rare, this study examined whether sex ratio and minor male morph frequency were associated with host age and sex and nematode infra-population size in the isolated Soay sheep population on St Kilda. Count data forTeladorsagiawere analysed for sheep of all age classes and both sexes from the winters of three consecutive population crashes (1999, 2002 and 2005). Generally, the intensity ofTeladorsagianematodes increased with host age until the age of 2 years before decreasing. In 2005, abundance of nematodes was generally higher than in the previous crashes, nematode sex ratio was negatively associated with host age and tended to be negatively associated with nematode intensity. Within the male nematode subpopulation,T. circumcinctaalways predominated, followed byT. davtianiand thenT. trifurcata, with little variation in the relative proportions between hosts. The presence of each minor morph was primarily associated with the intensity of maleT. circumcinctaand, in those hosts where all three male morphs were detected, intensity of each minor morph was most associated with intensity ofTeladorsagiafemales. Therefore, in a year when the nematode was generally more abundant, sex ratio appeared to be influenced by both host and nematode-related factors, whereas in all years examined, the frequency of morphological polymorphism was primarily density dependent.

Re-establishment of nematode infra-community and host survivorship in wild Soay sheep following anthelmintic treatment

Compared to mainland Britain, where there has been decades of anthelmintic use, the natural host-parasite relationship of the wild Soay sheep on the remote archipelago of St. Kilda has remained undisturbed. Small-scale anthelmintic bolus experiments on the island have previously shown that the removal of gastrointestinal nematodes can improve over-winter survival of young and male sheep in high host density years. This study, in which two-year-old sheep were treated, is the first to examine patterns of re-establishment of different nematode species in sheep following treatment and also investigates which species are likely to affect host survival. The experiment showed that, although all sheep were equally likely to die, host sex and weight influenced temporal survivorship in that females and heavier sheep tended to survive longer. Examination of the nematodes that had re-infected males six months after administration of an anthelmintic bolus showed that, compared to controls, the diversity of species was lower. Of the nine nematode species, there were fewer Trichostrongylus axei and Trichostrongylus vitrinus nematodes in treated sheep. In control sheep there were more T. axei and T. vitrinus nematodes in males than females. In addition there was an association between host over winter weight loss and the intensity of T. vitrinus. The fact that this species had higher numbers in males than females and was associated with over-winter weight loss implies it could have an important role in host mortality in high-density years.