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International journal for parasitology [journal]
- The parasitic phase of Ostertagia ostertagi: quantification of the main life history traits through systematic review and meta-analysis. [JOURNAL ARTICLE]
- Int J Parasitol 2014 Sep 13.
Predictive models of parasite life cycles increase our understanding of how parasite epidemiology is influenced by global changes and can be used to support decisions for more targeted worm control. Estimates of parasite population dynamics are needed to parameterize such models. The aim of this study was to quantify the main life history traits of Ostertagia ostertagi, economically the most important nematode of cattle in temperate regions. The main parameters determining parasite density during the parasitic phase of O. ostertagi are (i) the larval establishment rate, (ii) hypobiosis rate, (iii) adult mortality and (iv) female fecundity (number of eggs laid per day per female). A systematic review was performed covering studies from 1962 to 2007, in which helminth-naïve calves were artificially infected with O. ostertagi. The database was further extended with results of unpublished trials conducted at the Laboratory for Parasitology of Ghent University, Belgium. Overall inverse variance weighted estimates were computed for each of the traits through random effects models. An average establishment rate (± S.E.) of 0.269 ± 0.022 was calculated based on data of 27 studies (46 experiments). The establishment rate declined when infection dose increased and was lower in younger animals. An average proportion of larvae entering hypobiosis (± S.E.) of 0.041 (± 0.009) was calculated based on 27 studies (54 experiments). The proportion of ingested larvae that went into hypobiosis was higher in animals that received concomitant infections with nematode species other than O. ostertagi (mixed infections). An average daily adult mortality (± S.E.) of 0.028 (± 0.002) was computed based on data from 28 studies (70 experiments). Adult mortality was positively correlated with infection dose. A daily fecundity (± S.E.) of 284 (± 45) eggs per female was found based on nine studies (10 experiments). The average female sex ratio of O. ostertagi based on individual animal data (n = 75) from six different studies was estimated to be 0.55. We believe that this systematic review is the first to summarize the available data on the main life history traits of the parasitic phase of O. ostertagi. In conclusion, this meta-analysis provides novel estimates for the parameterization of life cycle-based transmission models, explicitly reports measures of variance around these estimates, gives evidence for density dependence of larval establishment and adult mortality, shows that host age affects larval establishment and, to our knowledge, provides the first evidence for O. ostertagi of a female-biased sex ratio.
- Comparison of next-generation droplet digital PCR (ddPCR) with quantitative PCR (qPCR) for enumeration of Cryptosporidium oocysts in faecal samples. [JOURNAL ARTICLE]
- Int J Parasitol 2014 Sep 13.
Clinical microbiology laboratories rely on quantitative PCR (qPCR) for its speed, sensitivity, specificity and ease-of-use. However, qPCR quantitation requires the use of a standard curve or normalization to reference genes. Droplet digital PCR (ddPCR) provides absolute quantitation without the need for calibration curves. A comparison between ddPCR and qPCR-based analyses was conducted for the enteric parasite Cryptosporidium, which is an important cause of gastritis in both humans and animals. Two loci were analysed (18S rRNA and actin) using a range of Cryptosporidium DNA templates, including recombinant plasmids, purified haemocytometer-counted oocysts, commercial flow cytometry-counted oocysts and faecal DNA samples from sheep, cattle and humans. Each method was evaluated for linearity, precision, limit of detection (LOD) and cost. Across the same range of detection, both methods showed a high degree of linearity and positive correlation for standards (R(2) ⩾ 0.999) and faecal samples (R(2) ⩾ 0.9750). The precision of ddPCR, as measured by mean Relative Standard Deviation (RSD;%), was consistently better compared with qPCR, particularly for the 18S rRNA locus, but was poorer as DNA concentration decreased. The quantitative detection of qPCR was unaffected by DNA concentration, but ddPCR qPCR was less affected by the presence of inhibitors, compared with qPCR. For most templates analysed including Cryptosporidium-positive faecal DNA, the template copy numbers, as determined by ddPCR, were consistently lower than by qPCR. However, the quantitations obtained by qPCR are dependent on the accuracy of the standard curve and when the qPCR data were corrected for pipetting and DNA losses (as determined by ddPCR), then the sensitivity of both methods was comparable. A cost analysis based on 96 samples revealed that the overall cost (consumables and labour) of ddPCR was two times higher than qPCR. Using ddPCR to precisely quantify standard dilutions used for high-throughput and cost-effective amplifications by qPCR would be one way to combine the advantages of the two technologies.
- A dyf-7 haplotype causes sensory neuron defects and is associated with macrocyclic lactone resistance worldwide in the nematode parasite Haemonchus contortus. [JOURNAL ARTICLE]
- Int J Parasitol 2014 Sep 12.
Heavy reliance on macrocyclic lactones (MLs) to treat parasitic nematodes has resulted in the evolution of widespread drug resistance that threatens human and animal health. Management strategies have been proposed that would slow the rise of resistance, however testing these strategies has been hampered by the lack of identified strong-effect resistance markers in parasites. We show that the Caenorhabditis elegans gene Cel_dyf-7, necessary for amphid sensory neuron development, also confers ML sensitivity. In the sheep parasite Haemonchus contortus: i) strains selected for ML resistance were enriched in a Hco_dyf-7 haplotype that was rare in the drug-naïve population, ii) the resistant haplotype correlated with the sensory neuron defects, and iii) the resistant haplotype was associated with decreased Hco_dyf-7 expression. Resistant field isolates of H. contortus from five continents were enriched for the resistant haplotype, demonstrating the relevance of the Hco_dyf-7 haplotype to practice and indicating that it is a locus of strong effect. Hemizygosity resulting from sex linkage of dyf-7 likely contributes to the rise of resistance in treated populations.
- Parasitic mites of medical and veterinary importance - is there a common research agenda? [REVIEW]
- Int J Parasitol 2014 Sep 10.
There are an estimated 0.5 - 1 million mite species on earth. Among the many mites that are known to affect humans and animals, only a subset are parasitic but these can cause significant disease. We aim here to provide an overview of the most recent work in this field in order to identify common biological features of these parasites and to inform common strategies for future research. There is a critical need for diagnostic tools to allow for better surveillance and for drugs tailored specifically to the respective parasites. Multi-'omics' approaches represent a logical and timely strategy to identify the appropriate mite molecules. Recent advances in sequencing technology enable us to generate de novo genome sequence data, even from limited DNA resources. Consequently, the field of mite genomics has recently emerged and will now rapidly expand, which is a particular advantage for parasitic mites that cannot be cultured in vitro. Investigations of the microbiota associated with mites will elucidate the link between parasites and pathogens, and define the role of the mite in transmission and pathogenesis. The databases generated will provide the crucial knowledge essential to design novel diagnostic tools, control measures, prophylaxes, drugs and immunotherapies against the mites and associated secondary infections.
- Trematodes of the Great Barrier Reef, Australia: emerging patterns of diversity and richness in coral reef fishes. [REVIEW]
- Int J Parasitol 2014 Sep 6.
The Great Barrier Reef holds the richest array of marine life found anywhere in Australia, including a diverse and fascinating parasite fauna. Members of one group, the trematodes, occur as sexually mature adult worms in almost all Great Barrier Reef bony fish species. Although the first reports of these parasites were made 100years ago, the fauna has been studied systematically for only the last 25years. When the fauna was last reviewed in 1994 there were 94 species known from the Great Barrier Reef and it was predicted that there might be 2,270 in total. There are now 326 species reported for the region, suggesting that we are in a much improved position to make an accurate prediction of true trematode richness. Here we review the current state of knowledge of the fauna and the ways in which our understanding of this fascinating group is changing. Our best estimate of the true richness is now a range, 1,100-1,800 species. However there remains considerable scope for even these figures to be incorrect given that fewer than one-third of the fish species of the region have been examined for trematodes. Our goal is a comprehensive characterisation of this fauna, and we outline what work needs to be done to achieve this and discuss whether this goal is practically achievable or philosophically justifiable.
- Parasite-induced alteration of odor responses in an amphipod-acanthocephalan system. [JOURNAL ARTICLE]
- Int J Parasitol 2014 Sep 5.
Odor-related behaviors in aquatic invertebrates are important and effective anti-predator behaviors. Parasites often alter invertebrate host behaviors to increase transmission to hosts. This study investigated the responses of the amphipod Hyalella azteca when presented with two predator chemical cues: (i) alarm pheromones produced by conspecifics and (ii) kairomones produced by a predatory Green Sunfish (Lepomis cyanellus). We compared the responses of amphipods uninfected and infected with the acanthocepalan parasite Leptorhynchiodes thecatus. Uninfected amphipods reduced activity and increased refuge use after detecting both the alarm pheromones and predator kairomones. Infected amphipods spent significantly more time being active and less time on the refuge than uninfected amphipods, and behaved as if they had not detected the chemical stimulus. Therefore, L. thecatus infections disrupt the amphipods' anti-predator behaviors and likely make their hosts more susceptible to predation.
- Liver fluke vaccines in ruminants: strategies, progress and future opportunities. [REVIEW]
- Int J Parasitol 2014 Sep 6.
The development of a vaccine for Fasciola spp. in livestock is a challenge and would be advanced by harnessing our knowledge of acquired immune mechanisms expressed by resistant livestock against fluke infection. Antibody-dependent cell-mediated cytotoxicity directed to the surface tegument of juvenile/immature flukes is a host immune effector mechanism, suggesting that antigens on the surface of young flukes may represent prime candidates for a fluke vaccine. A Type 1 immune response shortly after fluke infection is associated with resistance to infection in resistant sheep, indicating that vaccine formulations should attempt to induce Type 1 responses to enhance vaccine efficacy. In cattle or sheep, an optimal fluke vaccine would need to reduce mean fluke burdens in a herd below the threshold of 30-54 flukes to ensure sustainable production benefits. Fluke infection intensity data suggest that vaccine efficacy of approximately 80% is required to reduce fluke burdens below this threshold in most countries. With the increased global prevalence of triclabendazole-resistant Fasciolahepatica, it may be commercially feasible in the short term to introduce a fluke vaccine of reasonable efficacy that will provide economic benefits for producers in regions where chemical control of new drug-resistant fluke infections is not viable. Commercial partnerships will be needed to fast-track new candidate vaccines using acceptable adjuvants in relevant production animals, obviating the need to evaluate vaccine antigens in rodent models.
- Exploiting parallels between livestock and wildlife: Predicting the impact of climate change on gastrointestinal nematodes in ruminants. [Journal Article, Review]
- Int J Parasitol Parasites Wildl 2014 Aug; 3(2):209-19.
Global change, including climate, policy, land use and other associated environmental changes, is likely to have a major impact on parasitic disease in wildlife, altering the spatio-temporal patterns of transmission, with wide-ranging implications for wildlife, domestic animals, humans and ecosystem health. Predicting the potential impact of climate change on parasites infecting wildlife will become increasingly important in the management of species of conservation concern and control of disease at the wildlife-livestock and wildlife-human interface, but is confounded by incomplete knowledge of host-parasite interactions, logistical difficulties, small sample sizes and limited opportunities to manipulate the system. By exploiting parallels between livestock and wildlife, existing theoretical frameworks and research on livestock and their gastrointestinal nematodes can be adapted to wildlife systems. Similarities in the gastrointestinal nematodes and the life-histories of wild and domestic ruminants, coupled with a detailed knowledge of the ecology and life-cycle of the parasites, render the ruminant-GIN host-parasite system particularly amenable to a cross-disciplinary approach.
- Parasites as biological tags to assess host population structure: Guidelines, recent genetic advances and comments on a holistic approach. [Journal Article, Review]
- Int J Parasitol Parasites Wildl 2014 Aug; 3(2):220-6.
We review the use of parasites as biological tags of marine fishes and cephalopods in host population structure studies. The majority of the work published has focused on marine fish and either single parasite species or more recently, whole parasite assemblages, as biological tags. There is representation of host organisms and parasites from a diverse range of taxonomic groups, although focus has primarily been on host species of commercial importance. In contrast, few studies have used parasites as tags to assess cephalopod population structure, even though records of parasites infecting cephalopods are well-documented. Squid species are the only cephalopod hosts for which parasites as biological tags have been applied, with anisakid nematode larvae and metacestodes being the parasite taxa most frequently used. Following a brief insight into the importance of accurate parasite identification, the population studies that have used parasites as biological tags for marine fishes and cephalopods are reviewed, including comments on the dicyemid mesozoans. The advancement of molecular genetic techniques is discussed in regards to the new ways parasite genetic data can be incorporated into population structure studies, alongside host population genetic analyses, followed by an update on the guidelines for selecting a parasite species as a reliable tag candidate. As multiple techniques and methods can be used to assess the population structure of marine organisms (e.g. artificial tags, phenotypic characters, biometrics, life history, genetics, otolith microchemistry and parasitological data), we conclude by commenting on a holistic approach to allow for a deeper insight into population structuring.
- Genome-based vaccine design: the promise for malaria and other infectious diseases. [REVIEW]
- Int J Parasitol 2014 Sep 6.
Vaccines are one of the most effective interventions to improve public health, however, the generation of highly effective vaccines for many diseases has remained difficult. Three chronic diseases that characterise these difficulties include malaria, tuberculosis and HIV, and they alone account for half of the global infectious disease burden. The whole organism vaccine approach pioneered by Jenner in 1796 and refined by Pasteur in 1857 with the "isolate, inactive and inject" paradigm has proved highly successful for many viral and bacterial pathogens causing acute disease but has failed with respect to malaria, tuberculosis and HIV as well as many other diseases. A significant advance of the past decade has been the elucidation of the genomes, proteomes and transcriptomes of many pathogens. This information provides the foundation for new 21st Century approaches to identify target antigens for the development of vaccines, drugs and diagnostic tests. Innovative genome-based vaccine strategies have shown potential for a number of challenging pathogens, including malaria. We advocate that genome-based rational vaccine design will overcome the problem of poorly immunogenic, poorly protective vaccines that has plagued vaccine developers for many years.