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International journal for parasitology [journal]
- Host generalists and specialists emerging side by side: an analysis of evolutionary patterns in the cosmopolitan chewing louse genus Menacanthus. [JOURNAL ARTICLE]
- Int J Parasitol 2014 Oct 10.
Parasites with wide host spectra provide opportunities to study the ecological parameters of speciation, as well as the process of the evolution of host specificity. The speciose and cosmopolitan louse genus Menacanthus comprises both multi-host and specialised species, allowing exploration of the ecological and historical factors affecting the evolution of parasites using a comparative approach. We used phylogenetic analysis to reconstruct evolutionary relationships in 14 species of Menacanthus based on the sequences of one mitochondrial and one nuclear gene. The results allowed us to validate species identification based on morphology, as well as to explore host distribution by assumed generalist and specialist species. Our analyses confirmed a narrow host use for several species, however in some cases, the supposed host specialists had a wider host spectrum than anticipated. In one case a host generalist (Menacanthuseurysternus) was clustered terminally on a clade almost exclusively containing host specialists. Such a clade topology indicates that the process of host specialisation may not be irreversible in parasite evolution. Finally, we compared patterns of population genetic structure, geographic distribution and host spectra between two selected species, M. eurysternus and Menacanthus camelinus, using haplotype networks. Menacanthus camelinus showed limited geographical distribution in combination with monoxenous host use, whereas M. eurysternus showed a global distribution and lack of host specificity. It is suggested that frequent host switching maintains gene flow between M. eurysternus populations on unrelated hosts in local populations. However, gene flow between geographically distant localities was restricted, suggesting that geography rather than host-specificity is the main factor defining the global genetic diversity of M. eurysternus.
- The affinity of magnetic microspheres for Schistosoma eggs. [JOURNAL ARTICLE]
- Int J Parasitol 2014 Oct 7.
Schistosomiasis is a chronic parasitic disease of humans, with two species primarily causing the intestinal infection: Schistosoma mansoni and Schistosoma japonicum. Traditionally, diagnosis of schistosomiasis is achieved through direct visualisation of eggs in faeces using techniques that lack the sensitivity required to detect all infections, especially in areas of low endemicity. A recently developed method termed Helmintex™ is a very sensitive technique for detection of Schistosoma eggs and exhibits 100% sensitivity at 1.3 eggs per gram of faeces, enough to detect even low-level infections. The Helminthex™ method is based on the interaction of magnetic microspheres and schistosome eggs. Further understanding the underlying egg-microsphere interactions would enable a targeted optimisation of egg-particle binding and may thus enable a significant improvement of the Helmintex™ method and diagnostic sensitivity in areas with low infection rates. We investigated the magnetic properties of S. mansoni and S. japonicum eggs and their interactions with microspheres with different magnetic properties and surface functionalization. Eggs of both species exhibited higher binding affinity to the magnetic microspheres than the non-magnetic microspheres. Binding efficiency was further enhanced if the particles were coated with streptavidin. Schistosoma japonicum eggs bound more microspheres compared with S. mansoni. However, distinct differences within eggs of each species were also observed when the distribution of the number of microspheres bound per egg was modelled with double Poisson distributions. Using this approach, both S. japonicum and S. mansoni eggs fell into two groups, one having greater affinity for magnetic microspheres than the other, indicating that not all eggs of a species exhibit the same binding affinity. Our observations suggest that interaction between the microspheres and eggs is more likely to be related to surface charge-based electrostatic interactions between eggs and magnetic iron oxide rather than through a direct magnetic interaction.
- Mitochondrial genomes of Trichinella species and genotypes - a basis for diagnosis, and systematic and epidemiological explorations. [JOURNAL ARTICLE]
- Int J Parasitol 2014 Sep 22.
In the present study we sequenced or re-sequenced, assembled and annotated 15 mitochondrial genomes representing the 12 currently recognised taxa of Trichinella using a deep sequencing-coupled approach. We then defined and compared the gene order in individual mitochondrial genomes (∼14 to 17.7kb), evaluated genetic differences among species/genotypes and re-assessed the relationships among these taxa using the mitochondrial nucleic acid or amino acid sequence data sets. In addition, a rich source of mitochondrial genetic markers was defined that could be used in future systematic, epidemiological and population genetic studies of Trichinella. The sequencing-bioinformatic approach employed herein should be applicable to a wide range of eukaryotic parasites.
- Control of the sheep blowfly in Australia and New Zealand - are we there yet? [REVIEW]
- Int J Parasitol 2014 Sep 18.
The last 50years of research into infections in Australia and New Zealand caused by larvae of the sheep blowfly, Lucilia cuprina, have significantly advanced our understanding of this blowfly and its primary host, the sheep. However, apart from some highly effective drugs it could be argued that no new control methodologies have resulted. This review addresses the major areas of sheep blowfly research over this period describing the significant outcomes and analyses, and what is still required to produce new commercial control technologies. The use of drugs against this fly species has been very successful but resistance has developed to almost all current compounds. Integrated pest management is becoming basic to control, especially in the absence of mulesing, and has clearly benefited from computer-aided technologies. Biological control has more challenges but natural and perhaps transformed biopesticides offer possibilities for the future. Experimental vaccines have been developed but require further analysis of antigens and formulations to boost protection. Genetic technologies may provide potential for long-term control through more rapid indirect selection of sheep less prone to flystrike. Finally in the future, genetic analysis of the fly may allow suppression and perhaps eradication of blowfly populations or identification of new and more viable targets for drug and vaccine intervention. Clearly all these areas of research offer potential new controls but commercial development is perhaps inhibited by the success of current chemical insecticides and certainly requires a significant additional injection of resources.
- Divergent environmental preferences and areas of sympatry of tick species in the Amblyomma cajennense complex (Ixodidae). [JOURNAL ARTICLE]
- Int J Parasitol 2014 Sep 16.
Four species of Neotropical ticks, Amblyomma mixtum, Amblyomma cajennense, Amblyomma tonelliae and Amblyomma sculptum (formerly included in the catch-all name A. cajennense), have an allopatric distribution in much of their range, with areas of parapatry for at least two of them. We inferred the abiotic niches of these organisms using coefficients of a harmonic regression of the temperature and the Normalized Difference Vegetation Index (NDVI, reflecting plant stress) from remotely sensed data from MODIS satellites with 0.05° spatial resolution. Combinations of coefficients describing the phenology of these two variables pointed to divergent niche preferences, compatible with previous events of vicariance among the species. Amblyomma cajennense has been recorded in areas with small variations in temperature and NDVI. The remaining species were recorded in areas with large variations. The maximum environmental niche overlap was ∼73.6% between A. mixtum and A. cajennense and 73.5% between A. tonelliae and A. sculptum. Projecting these inferences on the geographical space revealed probable areas of sympatry or parapatry between A. mixtum and A. cajennense or between A. tonelliae and A. sculptum, the latter of which was confirmed with field collections. The A. sculptum distribution overlaps with that of A. tonelliae in northern Argentina and Paraguay; parapatry occurs at one extreme of the conditions occupied by both species. Compared with areas of allopatry, sites with both species had consistently lower temperatures, except for 10-12weeks during the summer, and higher NDVI values throughout the year. We hypothesise that the overlap between A. tonelliae and A. sculptum resulted from secondary contact between populations, with A. sculptum adapting to sites with high water availability to balance high summer temperatures. Additional surveys of the areas of spatial overlap among these species are necessary to elucidate the forces driving their evolution and their adaptation to the environment.
- A list of the 70 species of Australian ticks; diagnostic guides to and species accounts of Ixodes holocyclus (paralysis tick), Ixodes cornuatus (southern paralysis tick) and Rhipicephalus australis (Australian cattle tick); and consideration of the place of Australia in the evolution of ticks with comments on four controversial ideas. [REVIEW]
- Int J Parasitol 2014 Sep 15.
Seventy species of ticks are known from Australia: 14 soft ticks (family Argasidae) and 56 hard ticks (family Ixodidae). Sixteen of the 70 ticks in Australia may feed on humans and domestic animals (Barker and Walker 2014). The other 54 species of ticks in Australia feed only on wild mammals, reptiles and birds. At least 12 of the species of ticks in Australian also occur in Papua New Guinea. We use an image-matching system much like the image-matching systems of field guides to birds and flowers to identify Ixodes holocyclus (paralysis tick), Ixodes cornuatus (southern paralysis tick) and Rhipicephalus (Boophilus) australis (Australian cattle tick). Our species accounts have reviews of the literature on I. holocyclus (paralysis tick) from the first paper on the biology of an Australian tick by Bancroft (1884), on paralysis of dogs by I. holocyclus, to papers published recently, and of I. cornuatus (southern paralysis tick). We comment on four controversial questions in the evolutionary biology of ticks: (i) were labyrinthodont amphibians in Australia in the Devonian the first hosts of soft, hard and nuttalliellid ticks?; (ii) are the nuttalliellid ticks the sister-group to the hard ticks or the soft ticks?; (iii) is Nuttalliella namaqua the missing link between the soft and hard ticks?; and (iv) the evidence for a lineage of large bodied parasitiform mites (ticks plus the holothyrid mites plus the opiliocarid mites).
- 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 16.
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 summarise 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 16.
Clinical microbiology laboratories rely on quantitative PCR for its speed, sensitivity, specificity and ease-of-use. However, quantitative PCR quantitation requires the use of a standard curve or normalisation to reference genes. Droplet digital PCR provides absolute quantitation without the need for calibration curves. A comparison between droplet digital PCR and quantitative PCR-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 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 droplet digital PCR, as measured by mean Relative Standard Deviation (RSD;%), was consistently better compared with quantitative PCR, particularly for the 18S rRNA locus, but was poorer as DNA concentration decreased. The quantitative detection of quantitative PCR was unaffected by DNA concentration, but droplet digital PCR quantitative PCR was less affected by the presence of inhibitors, compared with quantitative PCR. For most templates analysed including Cryptosporidium-positive faecal DNA, the template copy numbers, as determined by droplet digital PCR, were consistently lower than by quantitative PCR. However, the quantitations obtained by quantitative PCR are dependent on the accuracy of the standard curve and when the quantitative PCR data were corrected for pipetting and DNA losses (as determined by droplet digital PCR), then the sensitivity of both methods was comparable. A cost analysis based on 96 samples revealed that the overall cost (consumables and labour) of droplet digital PCR was two times higher than quantitative PCR. Using droplet digital PCR to precisely quantify standard dilutions used for high-throughput and cost-effective amplifications by quantitative PCR 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.