Warwick Grant - Academia.edu (original) (raw)

Papers by Warwick Grant

International Journal for Parasitology: Drugs and Drug Resistance

International Journal for Parasitology: Parasites and Wildlife

Parasites & vectors, Jan 18, 2017

Wolbachia are intracellular bacteria found in arthropods and several filarial nematode species. T... more Wolbachia are intracellular bacteria found in arthropods and several filarial nematode species. The filarial Wolbachia have been proposed to be involved in the immunopathology associated with onchocerciasis. Higher Wolbachia-to-nematode ratios have been reported in the savannah-ecotype compared to the forest-ecotype, and have been interpreted as consistent with a correlation between Wolbachia density and disease severity. However, factors such as geographic stratification and ivermectin drug exposure can lead to significant genetic heterogeneity in the nematode host populations, so we investigated whether Wolbachia copy number variation is also associated with these underlying factors. Genomic DNA was prepared from single adult nematodes representing forest and savannah ecotypes sampled from Togo, Ghana, Côte d'Ivoire and Mali. A qPCR assay was developed to measure the number of Wolbachia genome(s) per nematode genome. Next-generation sequencing (NGS) was also used to measure re...

Background: Genetic surveillance of the human filarial parasite, Onchocerca volvulus, from onchoc... more Background: Genetic surveillance of the human filarial parasite, Onchocerca volvulus, from onchocerciasis endemic regions will ideally focus on genotyping individual infective larval stages collected from their intermediate host, Simuliid blackflies. However, blackflies also transmit other Onchocerca species, including the cattle parasite O. ochengi, which are difficult to distinguish from the human parasite based on morphological characteristics alone. This study describes a versatile approach to discriminate between O. volvulus and O. ochengi that is demonstrated using parasite infective larvae dissected from blackflies. Results: A speciation assay was designed based on genetic differentiation between O. volvulus and O. ochengi mitochondrial genome sequences that can be performed in high-throughput high-resolution melt (HRM)- or lower throughput conventional restriction fragment length polymorphism (RFLP) analyses. This assay was validated on 185 Onchocerca larvae dissected from b...

Nature Genetics, 2016

Soil transmitted nematodes, including Strongyloides, cause the most prevalent of the Neglected Tr... more Soil transmitted nematodes, including Strongyloides, cause the most prevalent of the Neglected Tropical Diseases. Here we compare the genomes of four Strongyloides spp., including the human pathogen S. stercoralis, and their close relatives that are facultatively parasitic (Parastrongyloides trichosuri) and free-living (Rhabditophanes sp). A significant paralogous expansion of key gene familiesastacin-like metallopeptidase and SCP/TAPS coding gene familiesis associated with the evolution of parasitism in this clade. Exploiting the unique Strongyloides life cycle we compare the transcriptome of its free-living and parasitic stages, finding that these same genes are upregulated in the parasitic stages, underscoring their role in nematode parasitism.

The macrocyclic lactone drug ivermectin has revolutionised the control of river blindness, a dise... more The macrocyclic lactone drug ivermectin has revolutionised the control of river blindness, a disease caused by infection with the filarial nematode Onchocerca volvulus, and of other filarial infections such as lymphatic filiariasis. The pathology of river blindness is caused by the host immune response to the presence of L1 stage parasite larvae (microfilaria) in the skin and eyes. Ivermectin arrests the progression of this pathology and relieves acute symptoms by first removing microfilaria from the skin and second acting as a contraceptive of adult female parasites so that up to one year is required before new microfilaria re-‐populate the skin. The combination of these activities has led to the near elimination of river blindness from central and south America and from some previously hyperendemic regions of sub‐Saharan Africa. At a molecular level, ivermectin is an irreversible agonist of inhibitory glutamate gated chloride channels on neurones and at the neuromuscular junctio...

Onchocerca volvulus is the causative agent of the human parasitic disease onchocerciasis and is r... more Onchocerca volvulus is the causative agent of the human parasitic disease onchocerciasis and is responsible for significant morbidity, ranging from severe dermatitis and skin lesions to visual impairment and ultimately, blindness. In Africa (where greater than 99% of the disease burden lies), onchocerciasis is predominantly controlled via mass community directed administration of the macrocyclic lactone, ivermectin, and aims to disrupt the transmission of O. volvulus by removing existing- and preventing new microfilaria from being transmitted by its vector, Simulium spp., from one host to the next. Understanding the population dynamics and the underlying genetic structure of O. volvulus populations is important for control campaigns, particularly in light on growing evidence of poor drug response by O. volvulus to ivermectin. We sought to characterize the effects of ivermectin treatment on O. volvulus population structure to determine if selection is occurring and the potential for ...

The paradigm for drug resistance as a consequence of persistent drug treatment and subsequent gen... more The paradigm for drug resistance as a consequence of persistent drug treatment and subsequent genetic selection often assumes a beneficial mutation at a single locus followed by rapid expansion of this resistance-conferring change throughout a population. This is certainly true for a number of organisms, including helminths. Although candidate gene approaches have been important in defining resistance mechanisms, unless they are fully penetrant, ie. a causative mutation is definitively responsible for resistance, they do not always explain the resistance and likely miss novel mechanisms that an organism may employ. This seems to be the case in the human filarial nematode, Onchocerca volvulus, whereby evidence of phenotypic and genetic change in discrete West African populations that have undergone multiple ivermectin treatments suggest resistance is occurring, yet candidate gene approaches are inconclusive. Using a combination of population genomic approaches, including pooled genom...

Onchocerca volvulus is the major cause of onchocerciasis (commonly known as river blindness), a h... more Onchocerca volvulus is the major cause of onchocerciasis (commonly known as river blindness), a human filarial disease that affects over 40 million individuals predominantly throughout West Africa. Mass community treatment using the anthelmintic drug, ivermectin, has been largely successful in reducing transmission rates and has resulted in elimination of the parasite in some previously hyper-endemic regions. However, in some communities, evidence of reduced drug efficacy and genetic change in worm populations that have experienced multiple drug treatments suggest ivermectin resistance may be developing. An analysis of Illumina next generation sequencing data to identify O. volvulus polymorphisms that differ between good and poor responders to ivermectin has revealed that the mitochondrial genome is over-represented amongst SNPs that differentiate between "good response" and "poor response" worm populations. Mitochondria and hence the mitochondrial genome may pla...

The paradigm of drug resistance via Darwinian selection assumes an initially rare “resistance” al... more The paradigm of drug resistance via Darwinian selection assumes an initially rare “resistance” allele at a single locus that rapidly increases in frequency following repeated drug treatments. Identification of such alleles has often relied on candidate gene approaches that cannot detect novel mechanisms and do not perform well if resistance is not a simple fully penetrant Mendelian trait. The analysis of macrocyclic lactone (ML) resistance in nematode parasites suggests that ML resistance may be a polygenic quantitative trait (QTL), so we have employed a genome wide association (GWAS) approach to analyse ML responses in Onchocerca volvulus that makes no assumptions about mechanism or mode of inheritance. Using several population genomic approaches, including pooled genome re-sequencing and RAD(restriction associated DNA)seq on individual worms, we have investigated the genome-wide impact of ivermectin treatment. We have uncovered multiple genomic regions that differentiate ivermecti...

The EMBO journal, 1983

Proteins can be extracted from the slime sheath of Dictyostelium discoideum slugs by denaturing a... more Proteins can be extracted from the slime sheath of Dictyostelium discoideum slugs by denaturing agents. A subset of these proteins is also released by cellulase digestion of the sheath, implying that protein-protein and protein-cellulose interactions are involved in sheath protein retention. It seems probable that the cellulose-associated sheath proteins are also associated with the cellulose of mature stalk cells. Monoclonal antibodies directed against sheath demonstrate extensive sharing of antigenic determinants between sheath proteins and a limited degree of antigenic sharing between sheath and slug cell proteins. All of the proteins recognised by these monoclonal antibodies are developmentally regulated. These results are discussed in terms of the structure of the sheath and its possible role(s) in D. discoideum development.

Wildlife Research, 2008

The suitability of the nematode Parastrongyloides trichosuri (Nematoda: Strongyloididae) as a gen... more The suitability of the nematode Parastrongyloides trichosuri (Nematoda: Strongyloididae) as a genetically modified vector for transmissible fertility control of introduced brushtail possums (Trichosurus vulpecula) is being explored in New Zealand. This review of progress in assessing the ecological and epidemiological characteristics of P. trichosuri against a set of essential properties for a suitable transmissible vector indicates that the parasite appears to have all the attributes of a highly effective vector, although additional information on persistence at low host density and on the outcome of competition between existing infection and new (recombinant) strains is needed to confirm this. Concerns have been raised about risks to possums and other marsupials in Australia from a genetically modified form of P. trichosuri. An international body with responsibility for managing consultation and debate about issues arising from the proposed use of genetically modified organisms fo...

PLoS ONE, 2013

Mitochondrial targeting signals (MTSs) are responsible for trafficking nuclear encoded proteins t... more Mitochondrial targeting signals (MTSs) are responsible for trafficking nuclear encoded proteins to their final destination within mitochondria. These sequences are diverse, sharing little amino acid homology and vary significantly in length, and although the formation of a positively-charged amphiphilic alpha helix within the MTS is considered to be necessary and sufficient to mediate import, such a feature does not explain their diversity, nor how such diversity influences target sequence function, nor how such dissimilar signals interact with a single, evolutionarily conserved import mechanism. An in silico analysis of 296 N-terminal, matrix destined MTSs from Homo sapiens, Mus musculus, Saccharomyces cerevisiae, Arabidopsis thaliana, and Oryza sativa was undertaken to investigate relationships between MTSs, and/or, relationships between an individual targeting signal sequence and the protein that it imports. We present evidence that suggests MTS diversity is influenced in part by physiochemical and N-terminal characteristics of their mature sequences, and that some of these correlated characteristics are evolutionarily maintained across a number of taxa. Importantly, some of these associations begin to explain the variation in MTS length and composition.

Parasitology, 2013

SUMMARYThe parasitic roundworms Strongyloides stercoralis (in man) and Strongyloides ratti (in ra... more SUMMARYThe parasitic roundworms Strongyloides stercoralis (in man) and Strongyloides ratti (in rats) employ environmentally controlled XX/XO sex determination with a pair of X chromosomes and two pairs of autosomes. Strongyloides papillosus (in sheep) has only two pairs of chromosomes, one of which combines the genetic material homologous to the S. ratti chromosomes X and I. This species creates males through the elimination of one copy of the portion related to the X chromosome (chromatin diminution). It is not clear which one of these two sex-determining mechanisms is ancestral. We demonstrate that Strongyloides vituli (in cattle) has two pairs of chromosomes like its very close relative S. papillosus whereas Parastrongyloides trichosuri, a closely related out-group to Strongyloides spp. in Australian brushtail possums, has three chromosome pairs and employs XX/XO sex determination. The X chromosome of P. trichosuri is homologous to the X chromosome of S. ratti. Our data strongly ...

Molecular and Biochemical Parasitology, 1990

The helminth Trichostrongylus colubriformis is a parasitic nematode infecting the small intestine... more The helminth Trichostrongylus colubriformis is a parasitic nematode infecting the small intestine of sheep. We report the isolation and characterization of a 30-kDa glycoprotein capable of partially protecting guinea-pigs against the parasite. This glyeoprotein is secreted by the L4 and adult parasitic stages of the worm. The sequence of three separate eDNA clones predicts the polypeptide to be about 15 kDa, with four N-linked carbohydrate chains and an internal disulphide bond. The clones also indicate the existence of sequence variability in this antigen. Limited sequence homology to a porcine intestinal peptide suggests an influence on host gut physiology.

International Journal for Parasitology, 2006

Parastrongyloides trichosuri is a nematode parasite of Australian brushtail possums that has an a... more Parastrongyloides trichosuri is a nematode parasite of Australian brushtail possums that has an alternative free-living life cycle which can be readily maintained indefinitely in a laboratory setting. The ability to maintain this parasite in a free-living cycle and induce it to parasitism at the free-living L1 stage makes this an excellent model for the study of genes associated with parasitism. A 70 kD protein from infective larvae of P. trichosuri that appears to be immunogenic in infected possums has been identified as a heat shock protein (Hsp)70 homologue. The complete gene for Pt-Hsp70 was cloned and sequenced. The protein encoded by the Pt-Hsp70 gene is the likely orthologue of the Caenorhabditis elegans protein, Hsp70A, also known as hsp-1. Reverse transcriptase-PCR data indicate that Pt-Hsp70 (designated Pt-hsp-1) is expressed at readily detectable levels in all developmental stages of both the parasitic and free-living P. trichosuri life cycles and the promoter is mildly inducible by heat shock. Bioinformatic analysis of expressed sequence tag databases indicates that C. elegans hsp-1 homologues, together with C. elegans hsp-3 homologues, are the predominant members of the Hsp70 superfamily that are normally expressed in parasitic stages of the Strongyloididae family. Promoter fusions to a b-galactosidase coding sequence were prepared and introduced into wild type C. elegans to produce transgenic nematodes. Reporter gene expression was clearly present within embryonic cells and within intestinal cells of larval and adult stages. Thus, the expression of the Pt-hsp-1 promoter within P. trichosuri and transgenic C. elegans appears similar to the known expression of C. elegans hsp-1. This promoter should be of value in efforts to develop genetic manipulation tools for P. trichosuri.