Publications by authors named "Fiona M Tomley"

57 Publications

Revisiting the Economic Impacts of and Its Control in European Intensive Broiler Systems With a Recursive Modeling Approach.

Front Vet Sci 2020 5;7:558182. Epub 2020 Nov 5.

Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom.

Ionophore compounds active against species are widely used in intensive broiler systems and have formed the backbone of coccidiosis control for almost 50 years. Producers, however, are under pressure to reduce ionophore use due to consumer concerns over antimicrobial usage in food animals, and antimicrobial resistance. Moreover, current vaccines against are commonly considered to be less cost-effective in intensive broiler systems, especially in Europe where attenuated live vaccines are used. An economic assessment of the impact of and the disease coccidiosis, including the cost implications of different efficacies of control, is therefore timely to provide evidence for industry and policy development. A mechanistic model of broiler production under varying infection and control states was used to construct a dataset from which system productivity can be measured. Coccidiosis impact increased rapidly as control efficacy decreased. In the total absence of control, median impact was found to maximize at between €2.55 and €2.97 in lost production per meter squared of broiler house over a 33 day growing period. Coccidiosis remains a major risk to intensive broiler systems and the model developed allows investigation of issues related to coccidiosis control, antimicrobial use and the development of antimicrobial resistance.
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http://dx.doi.org/10.3389/fvets.2020.558182DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7674784PMC
November 2020

Phylogenetic Inference Using Cytochrome C Oxidase Subunit I (COI) in the Poultry Red Mite, in the United Kingdom Relative to a European Framework.

Front Vet Sci 2020 21;7:553. Epub 2020 Aug 21.

Pathobiology and Population Sciences, The Royal Veterinary College, Brookmans Park, United Kingdom.

The poultry red mite ), an obligatory blood feeding ectoparasite, is primarily associated with laying hens where it is estimated to cause losses of ~€231 million per annum to European farmers. Moderate to high infestation levels result in negative impacts on hen welfare, including increased cannibalism, irritation, feather pecking, restlessness, anemia, and mortality. Acaricides are currently the prevailing method of population control for , although resistance against some classes of acaricide has been widely reported. The development of resistance highlights a growing need for research into alternative control methods, including the development of a suitable and effective vaccine. Understanding the genetic structure of populations can support improved management of acaricide resistance and sustainability of future vaccines, but limited data are currently available. The aim of this study was to characterize isolates from Europe, targeting the cytochrome c oxidase subunit 1 (COI) gene to gain an insight into population structure and genetic diversity of currently circulating mites. isolates were collected from Albania, Belgium, Croatia, Czech Republic, Denmark, France, Greece, Italy, the Netherlands, Portugal, Romania, Slovenia, Turkey and the United Kingdom. Genomic DNA was extracted from individual adult mites and a 681bp fragment of the COI gene was amplified and sequenced. Phylogenetic analyses of 195 COI sequences confirmed the presence of multiple lineages across Europe with 76 distinct haplotypes split across three main haplogroups and six sub-haplogroups. Importantly there is considerable inter- and intra-country variation across Europe, which could result from the movement of poultry or transfer of contaminated equipment and/or materials and husbandry practices.
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http://dx.doi.org/10.3389/fvets.2020.00553DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7472527PMC
August 2020

Re-calculating the cost of coccidiosis in chickens.

Vet Res 2020 Sep 14;51(1):115. Epub 2020 Sep 14.

Pathobiology and Population Sciences, Royal Veterinary College, Hawkshead Lane, North Mymms, AL9 7TA, UK.

Coccidiosis, caused by Eimeria species parasites, has long been recognised as an economically significant disease of chickens. As the global chicken population continues to grow, and its contribution to food security intensifies, it is increasingly important to assess the impact of diseases that compromise chicken productivity and welfare. In 1999, Williams published one of the most comprehensive estimates for the cost of coccidiosis in chickens, featuring a compartmentalised model for the costs of prophylaxis, treatment and losses, indicating a total cost in excess of £38 million in the United Kingdom (UK) in 1995. In the 25 years since this analysis the global chicken population has doubled and systems of chicken meat and egg production have advanced through improved nutrition, husbandry and selective breeding of chickens, and wider use of anticoccidial vaccines. Using data from industry representatives including veterinarians, farmers, production and health experts, we have updated the Williams model and estimate that coccidiosis in chickens cost the UK £99.2 million in 2016 (range £73.0-£125.5 million). Applying the model to data from Brazil, Egypt, Guatemala, India, New Zealand, Nigeria and the United States resulted in estimates that, when extrapolated by geographical region, indicate a global cost of ~ £10.4 billion at 2016 prices (£7.7-£13.0 billion), equivalent to £0.16/chicken produced. Understanding the economic costs of livestock diseases can be advantageous, providing baselines to evaluate the impact of different husbandry systems and interventions. The updated cost of coccidiosis in chickens will inform debates on the value of chemoprophylaxis and development of novel anticoccidial vaccines.
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http://dx.doi.org/10.1186/s13567-020-00837-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7488756PMC
September 2020

Vaccination with transgenic Eimeria tenella expressing Eimeria maxima AMA1 and IMP1 confers partial protection against high-level E. maxima challenge in a broiler model of coccidiosis.

Parasit Vectors 2020 Jul 10;13(1):343. Epub 2020 Jul 10.

Department of Pathobiology and Population Sciences, Royal Veterinary College, Hawkshead Lane, Hatfield, Hertforshire, AL9 7TA, UK.

Background: Poultry coccidiosis is a parasitic enteric disease with a highly negative impact on chicken production. In-feed chemoprophylaxis remains the primary method of control, but the increasing ineffectiveness of anticoccidial drugs, and potential future restrictions on their use has encouraged the use of commercial live vaccines. Availability of such formulations is constrained by their production, which relies on the use of live chickens. Several experimental approaches have been taken to explore ways to reduce the complexity and cost of current anticoccidial vaccines including the use of live vectors expressing relevant Eimeria proteins. We and others have shown that vaccination with transgenic Eimeria tenella parasites expressing Eimeria maxima Apical Membrane Antigen-1 or Immune Mapped Protein-1 (EmAMA1 and EmIMP1) partially reduces parasite replication after challenge with a low dose of E. maxima oocysts. In the present study, we have reassessed the efficacy of these experimental vaccines using commercial birds reared at high stocking densities and challenged with both low and high doses of E. maxima to evaluate how well they protect chickens against the negative impacts of disease on production parameters.

Methods: Populations of E. tenella parasites expressing EmAMA1 and EmIMP1 were obtained by nucleofection and propagated in chickens. Cobb500 broilers were immunised with increasing doses of transgenic oocysts and challenged two weeks later with E. maxima to quantify the effect of vaccination on parasite replication, local IFN-γ and IL-10 responses (300 oocysts), as well as impacts on intestinal lesions and body weight gain (10,000 oocysts).

Results: Vaccination of chickens with E. tenella expressing EmAMA1, or admixtures of E. tenella expressing EmAMA1 or EmIMP1, was safe and induced partial protection against challenge as measured by E. maxima replication and severity of pathology. Higher levels of protection were observed when both antigens were delivered and was associated with a partial modification of local immune responses against E. maxima, which we hypothesise resulted in more rapid immune recognition of the challenge parasites.

Conclusions: This study offers prospects for future development of multivalent anticoccidial vaccines for commercial chickens. Efforts should now be focused on the discovery of additional antigens for incorporation into such vaccines.
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http://dx.doi.org/10.1186/s13071-020-04210-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7350274PMC
July 2020

Poultry Coccidiosis: Design and Interpretation of Vaccine Studies.

Front Vet Sci 2020 26;7:101. Epub 2020 Feb 26.

Department of Pathobiology and Population Sciences, Royal Veterinary College, Hertfordshire, United Kingdom.

infection impacts upon chicken welfare and economic productivity of the poultry sector. Live coccidiosis vaccines for chickens have been available for almost 70 years, but the requirement to formulate blends of oocysts from multiple species makes vaccine production costly and logistically demanding. A multivalent vaccine that does not require chickens for its production and can induce protection against multiple species is highly desirable. However, despite the identification and testing of many vaccine candidate antigens, no recombinant coccidiosis vaccine has been developed commercially. Currently, assessment of vaccine efficacy against , and the disease coccidiosis, can be done only through vaccination and challenge experiments but the design of such studies has been highly variable. Lack of a "standard" protocol for assessing vaccine efficacy makes comparative evaluations very difficult, complicating vaccine development, and validation. The formulation and schedule of vaccination, the breed of chicken and choice of husbandry system, the species, strain, magnitude, and timing of delivery of the parasite challenge, and the parameters used to assess vaccine efficacy all influence the outcomes of experimental trials. In natural infections, the induction of strong cell mediated immune responses are central to the development of protective immunity against coccidiosis. Antibodies are generally regarded to be of lesser importance. Unfortunately, there are no specific immunological assays that can accurately predict how well a vaccine will protect against coccidiosis (i.e., no "correlates of protection"). Thus, experimental vaccine studies rely on assessing a variety of post-challenge parameters, including assessment of pathognomonic lesions, measurements of parasite replication such as oocyst output or quantification of genomes, and/or measurements of productivity such as body weight gain and feed conversion rates. Understanding immune responses to primary and secondary infection can inform on the most appropriate immunological assays. The discovery of new antigens for different species and the development of new methods of vaccine antigen delivery necessitates a more considered approach to assessment of novel vaccines with robust, repeatable study design. Careful consideration of performance and welfare factors that are genuinely relevant to chicken producers and vaccine manufacturers is essential.
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http://dx.doi.org/10.3389/fvets.2020.00101DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7054285PMC
February 2020

Life cycle stages, specific organelles and invasion mechanisms of species.

Parasitology 2020 03 18;147(3):263-278. Epub 2019 Nov 18.

The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms AL9 7TA, UK.

Apicomplexans, including species of Eimeria, pose a real threat to the health and wellbeing of animals and humans. Eimeria parasites do not infect humans but cause an important economic impact on livestock, in particular on the poultry industry. Despite its high prevalence and financial costs, little is known about the cell biology of these 'cosmopolitan' parasites found all over the world. In this review, we discuss different aspects of the life cycle and stages of Eimeria species, focusing on cellular structures and organelles typical of the coccidian family as well as genus-specific features, complementing some 'unknowns' with what is described in the closely related coccidian Toxoplasma gondii.
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http://dx.doi.org/10.1017/S0031182019001562DOI Listing
March 2020

Evaluation of vaccine delivery systems for inducing long-lived antibody responses to antigen in laying hens.

Avian Pathol 2019 Sep 2;48(sup1):S60-S74. Epub 2019 Jul 2.

Moredun Research Institute, Pentlands Science Park , Edinburgh , UK.

, the poultry red mite, is a global threat to the commercial egg-laying industry. Control of is difficult, with only a limited number of effective pesticides and non-chemical treatments available. Here, we characterize the candidate vaccine antigen cathepsin D-1 (Dg-CatD-1) and demonstrate that purified refolded recombinant Dg-Cat-D1 (rDg-CatD-1) is an active aspartyl proteinase which digests haemoglobin with a pH optimum of pH 4. Soluble protein extracts from also have haemoglobinase activity, with a pH optimum comparable to the recombinant protein, and both proteinase activities were inhibited by the aspartyl proteinase inhibitor Pepstatin A. Enzyme activity and the ubiquitous localization of Dg-CatD-1 protein in sections of adult female mites is consistent with Dg-CatD-1 being a lysosomal proteinase. Using Dg-CatD-1 as a model vaccine antigen, we compared vaccine delivery methods in laying hens via vaccination with: (i) purified rDg-CatD-1 with Montanide™ ISA 71 VG adjuvant; (ii) recombinant DNA vaccines for expression of rDg-CatD-1 and (iii) transgenic coccidial parasite expressing rDg-CatD-1. In two independent trials, only birds vaccinated with rDg-CatD-1 with Montanide™ ISA 71 VG produced a strong and long-lasting serum anti-rDg-Cat-D1 IgY response, which was significantly higher than that in control birds vaccinated with adjuvant only. Furthermore, we showed that egg-laying rates of mites fed on birds vaccinated with rDg-CatD-1 in Montanide™ ISA 71 VG was reduced significantly compared with mites fed on unvaccinated birds. cathepsin D-1 (Dg-CatD-1) digests haemoglobin Vaccination of hens with rDg-CatD-1 in Montanide™ ISA 71 VG results in long-lasting IgY levels Serum anti-rDg-CatD-1 antibodies reduce egg laying in after a single blood meal.
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http://dx.doi.org/10.1080/03079457.2019.1612514DOI Listing
September 2019

Laboratory Growth and Genetic Manipulation of Eimeria tenella.

Curr Protoc Microbiol 2019 06 27;53(1):e81. Epub 2019 Feb 27.

Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hertfordshire, United Kingdom.

Eimeria is a genus of apicomplexan parasites that contains a large number of species, most of which are absolutely host-specific. Seven species have been recognized to infect chickens. Infection of susceptible chickens results in an intestinal disease called coccidiosis, characterized by mucoid or hemorrhagic enteritis, which is associated with impaired feed conversion or mortality in severe cases. Intensive farming practices have increased the significance of coccidiosis since parasite transmission is favored by high-density housing of large numbers of susceptible chickens. Routine chemoprophylaxis and/or vaccination with live parasite vaccines provides effective control of Eimeria, although the emergence of drug resistance and the relative cost and production capacity of current vaccine lines can prove limiting. As pressure to reduce drug use in livestock production intensifies, novel vaccination strategies are needed. Development of effective protocols supporting genetic complementation of Eimeria species has until recently been hampered by their inability to replicate efficiently in vitro. Now, the availability of such protocols has raised the prospect of generating transgenic parasite lines that function as vaccine vectors to express and deliver heterologous antigens. For example, this technology has the potential to streamline the production of live anticoccidial vaccines through the generation of parasite lines that co-express immunoprotective antigens derived from multiple Eimeria species. In this paper we describe detailed protocols for genetic manipulation, laboratory growth, and in vivo propagation of Eimeria tenella parasites, which will encourage future work from other researchers to expand biological understanding of Eimeria through reverse genetics. © 2019 by John Wiley & Sons, Inc.
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http://dx.doi.org/10.1002/cpmc.81DOI Listing
June 2019

Dissecting the Genomic Architecture of Resistance to Parasitism in the Chicken.

Front Genet 2018 26;9:528. Epub 2018 Nov 26.

The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Edinburgh, United Kingdom.

Coccidiosis in poultry, caused by protozoan parasites of the genus , is an intestinal disease with substantial economic impact. With the use of anticoccidial drugs under public and political pressure, and the comparatively higher cost of live-attenuated vaccines, an attractive complementary strategy for control is to breed chickens with increased resistance to parasitism. Prior infection with leads to complete immunity against challenge with homologous strains, but only partial resistance to challenge with antigenically diverse heterologous strains. We investigate the genetic architecture of avian resistance to primary infection and heterologous strain secondary challenge using White Leghorn populations of derived inbred lines, C.B12 and 15I, known to differ in susceptibility to the parasite. An intercross population was infected with Houghton (H) strain, followed 3 weeks later by Weybridge (W) strain challenge, while a backcross population received a single W infection. The phenotypes measured were parasite replication (counting fecal oocyst output or qPCR for parasite numbers in intestinal tissue), intestinal lesion score (gross pathology, scale 0-4), and for the backcross only, serum interleukin-10 (IL-10) levels. Birds were genotyped using a high density genome-wide DNA array (600K, Affymetrix). Genome-wide association study located associations on chromosomes 1, 2, 3, and 5 following primary infection in the backcross population, and a suggestive association on chromosome 1 following heterologous W challenge in the intercross population. This mapped several megabases away from the quantitative trait locus (QTL) linked to the backcross primary W strain infection, suggesting different underlying mechanisms for the primary- and heterologous secondary- responses. Underlying pathways for those genes located in the respective QTL for resistance to primary infection and protection against heterologous challenge were related mainly to immune response, with IL-10 signaling in the backcross primary infection being the most significant. Additionally, the identified markers associated with IL-10 levels exhibited significant additive genetic variance. We suggest this is a phenotype of interest to the outcome of challenge, being scalable in live birds and negating the requirement for single-bird cages, fecal oocyst counts, or slaughter for sampling (qPCR).
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http://dx.doi.org/10.3389/fgene.2018.00528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6275401PMC
November 2018

Draft Genome Assembly of the Poultry Red Mite, .

Microbiol Resour Announc 2018 Nov 8;7(18). Epub 2018 Nov 8.

Moredun Research Institute (MRI), Edinburgh, United Kingdom.

The poultry red mite, , is a major worldwide concern in the egg-laying industry. Here, we report the first draft genome assembly and gene prediction of , based on combined PacBio and MinION long-read sequencing. The ∼959-Mb genome is predicted to encode 14,608 protein-coding genes.
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http://dx.doi.org/10.1128/MRA.01221-18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6256547PMC
November 2018

Impact of Coinfection on Colonization of the Chicken.

Infect Immun 2019 02 24;87(2). Epub 2019 Jan 24.

Pathobiology and Population Sciences, Royal Veterinary College, North Mymms, United Kingdom

can cause the disease coccidiosis in chickens. The direct and often detrimental impact of this parasite on chicken health, welfare, and productivity is well recognized; however, less is known about the secondary effects that infection may have on other gut pathogens. is the leading cause of human bacterial foodborne disease in many countries and has been demonstrated to exert negative effects on poultry welfare and production in some broiler lines. Previous studies have shown that concurrent infection can influence the colonization and replication of bacteria, such as and serovar Typhimurium. Through a series of coinfection experiments, this study evaluated the impact that infection had on colonization of chickens, including the influence of variations in parasite dose and sampling time after bacterial challenge. Coinfection with resulted in a significant increase in colonization in the cecum in a parasite dose-dependent manner but a significant decrease in colonization in the spleen and liver of chickens. The results were reproducible at 3 and 10 days after bacterial infection. This work highlights that not only has a direct impact on the health and well-being of chickens but can have secondary effects on important zoonotic pathogens.
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http://dx.doi.org/10.1128/IAI.00772-18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6346136PMC
February 2019

Phenotypic and genetic variation in the response of chickens to Eimeria tenella induced coccidiosis.

Genet Sel Evol 2018 Nov 21;50(1):63. Epub 2018 Nov 21.

The Roslin Institute, University of Edinburgh, Easter Bush, Midlothian, UK.

Background: Coccidiosis is a major contributor to losses in poultry production. With emerging constraints on the use of in-feed prophylactic anticoccidial drugs and the relatively high costs of effective vaccines, there are commercial incentives to breed chickens with greater resistance to this important production disease. To identify phenotypic biomarkers that are associated with the production impacts of coccidiosis, and to assess their covariance and heritability, 942 Cobb500 commercial broilers were subjected to a defined challenge with Eimeria tenella (Houghton). Three traits were measured: weight gain (WG) during the period of infection, caecal lesion score (CLS) post mortem, and the level of a serum biomarker of intestinal inflammation, i.e. circulating interleukin 10 (IL-10), measured at the height of the infection.

Results: Phenotypic analysis of the challenged chicken cohort revealed a significant positive correlation between CLS and IL-10, with significant negative correlations of both these traits with WG. Eigenanalysis of phenotypic covariances between measured traits revealed three distinct eigenvectors. Trait weightings of the first eigenvector, (EV1, eigenvalue = 59%), were biologically interpreted as representing a response of birds that were susceptible to infection, with low WG, high CLS and high IL-10. Similarly, the second eigenvector represented infection resilience/resistance (EV2, 22%; high WG, low CLS and high IL-10), and the third eigenvector tolerance (EV3, 19%; high WG, high CLS and low IL-10), respectively. Genome-wide association studies (GWAS) identified two SNPs that were associated with WG at the suggestive level.

Conclusions: Eigenanalysis separated the phenotypic impact of a defined challenge with E. tenella on WG, caecal inflammation/pathology, and production of IL-10 into three major eigenvectors, indicating that the susceptibility-resistance axis is not a single continuous quantitative trait. The SNPs identified by the GWAS for body weight were located in close proximity to two genes that are involved in innate immunity (FAM96B and RRAD).
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http://dx.doi.org/10.1186/s12711-018-0433-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6249784PMC
November 2018

Illumina Next Generation Sequencing for the Analysis of Populations in Commercial Broilers and Indigenous Chickens.

Front Vet Sci 2018 30;5:176. Epub 2018 Jul 30.

Department of Pathobiology and Population Sciences, Royal Veterinary College, North Mymms, Hertfordshire, United Kingdom.

species parasites can cause the enteric disease coccidiosis, most notably in chickens where the economic and welfare implications are significant. Seven species are recognized to infect chickens, although understanding of their regional occurrence, abundance, and population structure remains limited. Reports of circulating in chickens across much of the southern hemisphere with cryptic genotypes and the capacity to escape current anticoccidial vaccines have revealed unexpected levels of complexity. Consequently, it is important to supplement validated species-specific molecular diagnostics with new genus-level tools. Here, we report the application of Illumina MiSeq deep sequencing to partial 18S rDNA amplicons generated using genus-specific primers from chicken caecal contents collected in India. Commercial Cobb400 broiler and indigenous Kadaknath type chickens were sampled under field conditions after co-rearing (mixed type farms, = 150 chickens for each) or separate rearing (single type farms, = 150 each). Comparison of MiSeq results with established Internal Transcribed Spacer (ITS) and Sequence Characterised Amplified Region (SCAR) quantitative PCR assays suggest greater sensitivity for the MiSeq approach. The caecal-dwelling and dominated each sample set, although all seven species which infect chickens were detected. Two of the three cryptic genotypes were detected including OTU-X and OTU-Y, the most northern report for the latter to date. Low levels of DNA representing other species were detected, possibly representing farm-level contamination with non-replicating oocysts or DNA, or false positives, indicating a requirement for additional validation. Next generation deep amplicon sequencing offers a valuable resource for future studies.
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http://dx.doi.org/10.3389/fvets.2018.00176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6077195PMC
July 2018

Microbial diversity and community composition of caecal microbiota in commercial and indigenous Indian chickens determined using 16s rDNA amplicon sequencing.

Microbiome 2018 06 23;6(1):115. Epub 2018 Jun 23.

Department of Animal Biotechnology, College of Veterinary Science and Animal Husbandry, Anand Agricultural University, Anand, Gujarat, 388001, India.

Background: The caecal microbiota plays a key role in chicken health and performance, influencing digestion and absorption of nutrients, and contributing to defence against colonisation by invading pathogens. Measures of productivity and resistance to pathogen colonisation are directly influenced by chicken genotype, but host driven variation in microbiome structure is also likely to exert a considerable indirect influence.

Methods: Here, we define the caecal microbiome of indigenous Indian Aseel and Kadaknath chicken breeds and compare them with the global commercial broiler Cobb400 and Ross 308 lines using 16S rDNA V3-V4 hypervariable amplicon sequencing.

Results: Each caecal microbiome was dominated by the genera Bacteroides, unclassified bacteria, unclassified Clostridiales, Clostridium, Alistipes, Faecalibacterium, Eubacterium and Blautia. Geographic location (a measure recognised to include variation in environmental and climatic factors, but also likely to feature varied management practices) and chicken line/breed were both found to exert significant impacts (p < 0.05) on caecal microbiome composition. Linear discriminant analysis effect size (LEfSe) revealed 42 breed-specific biomarkers in the chicken lines reared under controlled conditions at two different locations.

Conclusion: Chicken breed-specific variation in bacterial occurrence, correlation between genera and clustering of operational taxonomic units indicate scope for quantitative genetic analysis and the possibility of selective breeding of chickens for defined enteric microbiota.
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http://dx.doi.org/10.1186/s40168-018-0501-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6015460PMC
June 2018

Development of cross-protective Eimeria-vectored vaccines based on apical membrane antigens.

Int J Parasitol 2018 06 7;48(7):505-518. Epub 2018 Mar 7.

Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hertfordshire, United Kingdom.

Recently, the availability of protocols supporting genetic complementation of Eimeria has raised the prospect of generating transgenic parasite lines which can function as vaccine vectors, expressing and delivering heterologous proteins. Complementation with sequences encoding immunoprotective antigens from other Eimeria spp. offers an opportunity to reduce the complexity of species/strains in anticoccidial vaccines. Herein, we characterise and evaluate EtAMA1 and EtAMA2, two members of the apical membrane antigen (AMA) family of parasite surface proteins from Eimeria tenella. Both proteins are stage-regulated, and the sporozoite-specific EtAMA1 is effective at inducing partial protection against homologous challenge with E. tenella when used as a recombinant protein vaccine, whereas the merozoite-specific EtAMA2 is not. In order to test the ability of transgenic parasites to confer heterologous protection, E. tenella parasites were complemented with EmAMA1, the sporozoite-specific orthologue of EtAMA1 from E. maxima, coupled with different delivery signals to modify its trafficking and improve antigen exposure to the host immune system. Vaccination of chickens using these transgenic parasites conferred partial protection against E. maxima challenge, with levels of efficacy comparable to those obtained using recombinant protein or DNA vaccines. In the present work we provide evidence for the first known time of the ability of transgenic Eimeria to induce cross protection against different Eimeria spp. Genetically complemented Eimeria provide a powerful tool to streamline the complex multi-valent anticoccidial vaccine formulations that are currently available in the market by generating parasite lines expressing vaccine targets from multiple eimerian species.
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http://dx.doi.org/10.1016/j.ijpara.2018.01.003DOI Listing
June 2018

Characterization of novel microneme adhesive repeats (MAR) in Eimeria tenella.

Parasit Vectors 2017 Oct 17;10(1):491. Epub 2017 Oct 17.

Department of Pathobiology and Population Sciences, The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire, AL9 7TA, UK.

Background: The phylum Apicomplexa comprises a wide variety of parasites of significant medical and economic relevance. These parasites have extremely different host and tissue tropisms; for example Toxoplasma gondii can invade virtually any nucleated cell and infect almost all warm-blooded vertebrates, whereas Eimeria tenella infects only chickens and is restricted in its growth to epithelial cells of the caecum. Proteins released from the microneme secretory organelles (MICs) are critical for apicomplexan invasion of host cells and allow parasites to bind a diverse range of host cell oligosaccharide epitopes. MICs bear modular arrangements of sequences with adhesive proteins and interestingly the sialic-acid binding MAR (microneme adhesive repeat) domain containing proteins (MCPs) are suggested to make significant contributions to the different host and tissue tropisms of T. gondii and E. tenella.

Results: In this study, we evaluated the binding capacity of Type I MAR domains from novel E. tenella MCPs. Variants of the previously described HxT motif were analysed showing that HxT and VxT variants bind, whereas HxS and YxE variants did not. One of these MCP containing a single MAR (EtMCP2) showed an apical localization when expressed as a fusion with the fluorescent reporter mCherry in transgenic populations and a similar pattern of transcripts per zoite during endogenous development in vitro as the well-characterised microneme protein EtMIC2.

Conclusions: Variation in the binding properties of the MAR of different EtMCPs was confirmed and their ability to bind a wider range of sialic acids and terminal linkages should be studied. In addition, transgenesis technology has been used for first time in Eimeria parasites as a rapid tool for the study of endogenous protein localization by fusion with a fluorescent reporter.
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http://dx.doi.org/10.1186/s13071-017-2454-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5646145PMC
October 2017

Recombinant anticoccidial vaccines - a cup half full?

Infect Genet Evol 2017 11 7;55:358-365. Epub 2017 Oct 7.

Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hawkshead Lane, Hertfordshire AL9 7TA, UK.

Eimeria species parasites can cause the disease coccidiosis, most notably in chickens. The occurrence of coccidiosis is currently controlled through a combination of good husbandry, chemoprophylaxis and/or live parasite vaccination; however, scalable, cost-effective subunit or recombinant vaccines are required. Many antigens have been proposed for use in novel anticoccidial vaccines, supported by the capacity to reduce disease severity or parasite replication, increase body weight gain in the face of challenge or improve feed conversion under experimental conditions, but none has reached commercial development. Nonetheless, the protection against challenge induced by some antigens has been within the lower range described for the ionophores against susceptible isolates or current live vaccines prior to oocyst recycling. With such levels of efficacy it may be that combinations of anticoccidial antigens already described are sufficient for development as novel multi-valent vaccines, pending identification of optimal delivery systems. Selection of the best antigens to be included in such vaccines can be informed by knowledge defining the natural occurrence of specific antigenic diversity, with relevance to the risk of immediate vaccine breakthrough, and the rate at which parasite genomes can evolve new diversity. For Eimeria, such data are now becoming available for antigens such as apical membrane antigen 1 (AMA1) and immune mapped protein 1 (IMP1) and more are anticipated as high-capacity, high-throughput sequencing technologies become increasingly accessible.
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http://dx.doi.org/10.1016/j.meegid.2017.10.009DOI Listing
November 2017

Effects of Eimeria tenella infection on chicken caecal microbiome diversity, exploring variation associated with severity of pathology.

PLoS One 2017 21;12(9):e0184890. Epub 2017 Sep 21.

Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hatfield, United Kingdom.

Eimeria species cause the intestinal disease coccidiosis, most notably in poultry. While the direct impact of coccidiosis on animal health and welfare is clear, its influence on the enteric microbiota and by-stander effects on chicken health and production remains largely unknown, with the possible exception of Clostridium perfringens (necrotic enteritis). This study evaluated the composition and structure of the caecal microbiome in the presence or absence of a defined Eimeria tenella challenge infection in Cobb500 broiler chickens using 16S rRNA amplicon sequencing. The severity of clinical coccidiosis in individual chickens was quantified by caecal lesion scoring and microbial changes associated with different lesion scores identified. Following E. tenella infection the diversity of taxa within the caecal microbiome remained largely stable. However, infection induced significant changes in the abundance of some microbial taxa. The greatest changes were detected in birds displaying severe caecal pathology; taxa belonging to the order Enterobacteriaceae were increased, while taxa from Bacillales and Lactobacillales were decreased with the changes correlated with lesion severity. Significantly different profiles were also detected in infected birds which remained asymptomatic (lesion score 0), with taxa belonging to the genera Bacteroides decreased and Lactobacillus increased. Many differential taxa from the order Clostridiales were identified, with some increasing and others decreasing in abundance in Eimeria-infected animals. The results support the view that caecal microbiome dysbiosis associated with Eimeria infection contributes to disease pathology, and could be a target for intervention to mitigate the impact of coccidiosis on poultry productivity and welfare. This work highlights that E. tenella infection has a significant impact on the abundance of some caecal bacteria with notable differences detected between lesion score categories emphasising the importance of accounting for differences in caecal lesions when investigating the relationship between E. tenella and the poultry intestinal microbiome.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0184890PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5608234PMC
October 2017

Humoral and cytokine response elicited during immunisation with recombinant Immune Mapped protein-1 (EtIMP-1) and oocysts of Eimeria tenella.

Vet Parasitol 2017 Sep 24;244:44-53. Epub 2017 Jul 24.

Division of Parasitology, Indian Veterinary Research Institute, Izatnagar, Bareilly, Uttar Pradesh, PIN-243122, India. Electronic address:

Eimeria tenella, the causative agent of caecal coccidiosis, is a pathogenic gut dwelling protozoan which can cause severe morbidity and mortality in farmed chickens. Immune mapped protein-1 (IMP-1) has been identified as an anticoccidial vaccine candidate; in the present study allelic polymorphism was assessed across the IMP-1 coding sequence in E. tenella isolates from four countries and compared with the UK reference Houghton strain. Nucleotide diversity was low, limited to expansion/contraction of a CAG triplet repeat and five substitutions, three of which were non-synonymous. The EtIMP-1 coding sequence from a cloned Indian E. tenella isolate was expressed in E. coli and purified as a His-tagged thioredoxin fusion protein. An in-vivo vaccination and challenge trial was conducted to test the vaccine potential of recombinant EtIMP-1 (rEtIMP-1) and to compare post-vaccination immune responses of chickens to those stimulated by live oocyst infection. Following challenge, parasite replication measured using quantitative PCR was significantly reduced in chickens that had been vaccinated with rEtIMP-1 (rIC group; 67% reduction compared to UC or unimmunised controls; 79% reduction compared to rTC group or recombinant thioredoxin mock-immunised controls, p<0.05), or the birds vaccinated by infection with oocysts (OC group, 90% compared to unimmunised controls). Chickens vaccinated with oocysts (OC) had significantly higher levels of interferon gamma in their serum post-challenge, compared to rEtIMP-1 vaccinated birds (rIC). Conversely rEtIMP-1 (rIC) vaccinated birds had significantly higher antigen specific serum IgY responses, correlating with higher serum IL-4 (both p<0.05).
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http://dx.doi.org/10.1016/j.vetpar.2017.07.025DOI Listing
September 2017

Application of a new PCR-RFLP panel suggests a restricted population structure for Eimeria tenella in UK and Irish chickens.

Vet Parasitol 2016 Oct 26;229:60-67. Epub 2016 Sep 26.

Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, AL9 7TA, UK. Electronic address:

Eimeria species cause coccidiosis, most notably in chickens where the global cost exceeds US$3 billion every year. Understanding variation in Eimeria population structure and genetic diversity contributes valuable information that can be used to minimise the impact of drug resistance and develop new, cost-effective anticoccidial vaccines. Little knowledge is currently available on the epidemiology of Eimeria species and strains in different regions, or under different chicken production systems. Recently, 244 Eimeria tenella isolates collected from countries in Africa and Asia were genotyped using a Sequenom single nucleotide polymorphism (SNP) tool, revealing significant variation in haplotype diversity and population structure, with a marked North/South regional divide. To expand studies on genetic polymorphism to larger numbers of E. tenella populations in other geographic regions a cheaper and more accessible technique, such as polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), is desirable. We have converted a subset of SNP markers for use as PCR-RFLPs and re-analysed the original 244 isolates with the PCR-RFLPs to assess their utility. In addition, application of the PCR-RFLP to E. tenella samples collected from UK and Irish broiler chickens revealed a tightly restricted haplotype diversity. Just two of the PCR-RFLPs accounted for all of the polymorphism detected in the UK and Irish parasite populations, but analysis of the full dataset revealed different informative markers in different regions, supporting validity of the PCR-RFLP panel. The tools described here provide an accessible and cost-effective method that can be used to enhance understanding of E. tenella genetic diversity and population structure.
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http://dx.doi.org/10.1016/j.vetpar.2016.09.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5108357PMC
October 2016

Are Eimeria Genetically Diverse, and Does It Matter?

Trends Parasitol 2017 03 1;33(3):231-241. Epub 2016 Sep 1.

Department of Pathology and Pathogen Biology, Royal Veterinary College, North Mymms, Hertfordshire, UK. Electronic address:

Eimeria pose a risk to all livestock species as a cause of coccidiosis, reducing productivity and compromising animal welfare. Pressure to reduce drug use in the food chain makes the development of cost-effective vaccines against Eimeria essential. For novel vaccines to be successful, understanding genetic and antigenic diversity in field populations is key. Eimeria species that infect chickens are most significant, with Eimeria tenella among the best studied and most economically important. Genome-wide single nucleotide polymorphism (SNP)-based haplotyping has been used to determine population structure, genotype distribution, and potential for cross-fertilization between E. tenella strains. Here, we discuss recent developments in our understanding of diversity for Eimeria in relation to its specialized life cycle, distribution across the globe, and the challenges posed to vaccine development.
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http://dx.doi.org/10.1016/j.pt.2016.08.007DOI Listing
March 2017

Viral proteins expressed in the protozoan parasite Eimeria tenella are detected by the chicken immune system.

Parasit Vectors 2016 08 23;9:463. Epub 2016 Aug 23.

The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms, AL9 7TA, UK.

Background: Eimeria species are parasitic protozoa that cause coccidiosis, an intestinal disease commonly characterised by malabsorption, diarrhoea and haemorrhage that is particularly important in chickens. Vaccination against chicken coccidiosis is effective using wild-type or attenuated live parasite lines. The development of protocols to express foreign proteins in Eimeria species has opened up the possibility of using Eimeria live vaccines to deliver heterologous antigens and function as multivalent vaccine vectors that could protect chickens against a range of pathogens.

Results: In this study, genetic complementation was used to express immunoprotective virus antigens in Eimeria tenella. Infectious bursal disease virus (IBDV) causes Gumboro, an immunosuppressive disease that affects productivity and can interfere with the efficacy of poultry vaccination programmes. Infectious laryngotracheitis virus (ILTV) causes a highly transmissible respiratory disease for which strong cellular immunity and antibody responses are required for effective vaccination. Genes encoding the VP2 protein from a very virulent strain of IBDV (vvVP2) and glycoprotein I from ILTV (gI) were cloned downstream of 5'Et-Actin or 5'Et-TIF promoter regions in plasmids that also contained a mCitrine fluorescent reporter cassette under control of the 5'Et-MIC1 promoter. The plasmids were introduced by nucleofection into E. tenella sporozoites, which were then used to infect chickens. Progeny oocysts were sorted by FACS and passaged several times in vivo until the proportion of fluorescent parasites in each transgenic population reached ~20 % and the number of transgene copies per parasite genome decreased to < 10. All populations were found to transcribe and express the transgene and induced the generation of low titre, transgene-specific antibodies when used to immunise chickens.

Conclusions: E. tenella can express antigens of other poultry pathogens that are successfully recognised by the chicken immune system. Nonetheless, further work has to be done in order to improve the levels of expression for its future use as a multivalent vaccine vector.
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http://dx.doi.org/10.1186/s13071-016-1756-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4994267PMC
August 2016

Cryptic Eimeria genotypes are common across the southern but not northern hemisphere.

Int J Parasitol 2016 08 29;46(9):537-44. Epub 2016 Jun 29.

Department of Pathology and Pathogen Biology, Royal Veterinary College, North Mymms, Hertfordshire, UK. Electronic address:

The phylum Apicomplexa includes parasites of medical, zoonotic and veterinary significance. Understanding the global distribution and genetic diversity of these protozoa is of fundamental importance for efficient, robust and long-lasting methods of control. Eimeria spp. cause intestinal coccidiosis in all major livestock animals and are the most important parasites of domestic chickens in terms of both economic impact and animal welfare. Despite having significant negative impacts on the efficiency of food production, many fundamental questions relating to the global distribution and genetic variation of Eimeria spp. remain largely unanswered. Here, we provide the broadest map yet of Eimeria occurrence for domestic chickens, confirming that all the known species (Eimeria acervulina, Eimeria brunetti, Eimeria maxima, Eimeria mitis, Eimeria necatrix, Eimeria praecox, Eimeria tenella) are present in all six continents where chickens are found (including 21 countries). Analysis of 248 internal transcribed spacer sequences derived from 17 countries provided evidence of possible allopatric diversity for species such as E. tenella (FST values ⩽0.34) but not E. acervulina and E. mitis, and highlighted a trend towards widespread genetic variance. We found that three genetic variants described previously only in Australia and southern Africa (operational taxonomic units x, y and z) have a wide distribution across the southern, but not the northern hemisphere. While the drivers for such a polarised distribution of these operational taxonomic unit genotypes remains unclear, the occurrence of genetically variant Eimeria may pose a risk to food security and animal welfare in Europe and North America should these parasites spread to the northern hemisphere.
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http://dx.doi.org/10.1016/j.ijpara.2016.05.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4978698PMC
August 2016

Three operational taxonomic units of Eimeria are common in Nigerian chickens and may undermine effective molecular diagnosis of coccidiosis.

BMC Vet Res 2016 Jun 4;12:86. Epub 2016 Jun 4.

Faculty of Veterinary Medicine, Ahmadu Bello University, Zaria, Nigeria.

Background: Chicken is fast becoming the world's most consumed meat. As a consequence poultry health is more important now than ever before, with pathogens of chickens recognised as serious threats to food security. One such threat are Eimeria species parasites, protozoa which can cause the disease coccidiosis. Eimeria can compromise economic poultry production and chicken welfare, and have serious consequences for poor livestock keepers. Seven Eimeria species that infect chickens are recognised with a global enzootic distribution. More recently three cryptic Operational Taxonomic Units (OTUx, y and z) have been described in populations of Eimeria recovered from chickens in Australia. Two of the three OTUs have also been detected in sub-Saharan Africa, but their occurrence, pathology and the risk they pose is largely unknown.

Results: Nigeria has witnessed a dramatic expansion in poultry production and is now the largest poultry producer in Africa. Here, faecal samples collected from nine of 12 commercial chicken farms sampled in Kaduna state, Nigeria, were found to contain eimerian oocysts. After amplification by in vivo propagation all three cryptic OTU genotypes were detected using polymerase chain reaction (PCR), including OTUy for the first time outside of Australia. Comparison with a widely used, established Eimeria species-specific PCR assay revealed failure to detect the OTU genotypes.

Conclusions: All three of the Eimeria OTU genotypes appear to be common in north-western Nigeria. The failure of a leading species-specific molecular assay to detect these genotypes indicates a risk of false negative Eimeria diagnosis when using molecular tools and suggests that the spatial occurrence of each OTU may be far wider than has been recognised. The risk posed by these novel genotypes is unknown, but it is clear that a better understanding of Eimeria occurrence is required together with the validation of effective diagnostics.
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http://dx.doi.org/10.1186/s12917-016-0713-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4893269PMC
June 2016

Analysis of the function of IL-10 in chickens using specific neutralising antibodies and a sensitive capture ELISA.

Dev Comp Immunol 2016 10 22;63:206-12. Epub 2016 Apr 22.

The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian EH25 9RG, UK. Electronic address:

In mammals, the inducible cytokine interleukin 10 is a feedback negative regulator of inflammation. To determine the extent to which this function is conserved in birds, recombinant chicken IL-10 was expressed as a secreted human Ig Fc fusion protein (chIL-10-Fc) and used to immunise mice. Five monoclonal antibodies (mAb) which specifically recognise chicken IL-10 were generated and characterised. Two capture ELISA assays were developed which detected native chIL-10 secreted from chicken bone marrow-derived macrophages (chBMMs) stimulated with lipopolysaccharide (LPS). Three of the mAbs detected intracellular IL-10. This was detected in only a subset of the same LPS-stimulated chBMMs. The ELISA assay also detected massive increases in circulating IL-10 in chickens challenged with the coccidial parasite, Eimeria tenella. The same mAbs neutralised the bioactivity of recombinant chIL-10. The role of IL-10 in feedback control was tested in vitro. The neutralising antibodies prevented IL-10-induced inhibition of IFN-γ synthesis by mitogen-activated lymphocytes and increased nitric oxide production in LPS-stimulated chBMMs. The results confirm that IL-10 is an inducible feedback regulator of immune response in chickens, and could be the target for improved vaccine efficacy or breeding strategies.
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http://dx.doi.org/10.1016/j.dci.2016.04.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4947970PMC
October 2016

Population, genetic, and antigenic diversity of the apicomplexan Eimeria tenella and their relevance to vaccine development.

Proc Natl Acad Sci U S A 2015 Sep 9;112(38):E5343-50. Epub 2015 Sep 9.

Pathology and Pathogen Biology, Royal Veterinary College, North Mymms, Hertfordshire, AL9 7TA, United Kingdom;

The phylum Apicomplexa includes serious pathogens of humans and animals. Understanding the distribution and population structure of these protozoan parasites is of fundamental importance to explain disease epidemiology and develop sustainable controls. Predicting the likely efficacy and longevity of subunit vaccines in field populations relies on knowledge of relevant preexisting antigenic diversity, population structure, the likelihood of coinfection by genetically distinct strains, and the efficiency of cross-fertilization. All four of these factors have been investigated for Plasmodium species parasites, revealing both clonal and panmictic population structures with exceptional polymorphism associated with immunoprotective antigens such as apical membrane antigen 1 (AMA1). For the coccidian Toxoplasma gondii only genomic diversity and population structure have been defined in depth so far; for the closely related Eimeria species, all four variables are currently unknown. Using Eimeria tenella, a major cause of the enteric disease coccidiosis, which exerts a profound effect on chicken productivity and welfare, we determined population structure, genotype distribution, and likelihood of cross-fertilization during coinfection and also investigated the extent of naturally occurring antigenic diversity for the E. tenella AMA1 homolog. Using genome-wide Sequenom SNP-based haplotyping, targeted sequencing, and single-cell genotyping, we show that in this coccidian the functionality of EtAMA1 appears to outweigh immune evasion. This result is in direct contrast to the situation in Plasmodium and most likely is underpinned by the biology of the direct and acute coccidian life cycle in the definitive host.
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http://dx.doi.org/10.1073/pnas.1506468112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586875PMC
September 2015

Quantitative real-time PCR (qPCR) for Eimeria tenella replication--Implications for experimental refinement and animal welfare.

Parasitol Int 2015 Oct 2;64(5):464-70. Epub 2015 Jul 2.

Department of Pathology and Pathogen Biology, Royal Veterinary College, University of London, Hatfield AL9 7TA, United Kingdom. Electronic address:

The Eimeria species are highly pathogenic parasites of chickens. Research aimed at reducing their impact is hindered by a lack of non-subjective, quantitative, tools to measure parasite replication in the host. The time-consuming, and often time-sensitive, nature of existing approaches precludes their use in large-scale genetic, epidemiological, and evolutionary analyses. We have used quantitative real-time PCR (qPCR) to accurately quantify Eimeria tenella in chicken tissue and shown this to be more efficient and sensitive than traditional methodologies. We tested four chicken-specific reference qPCR assays and found beta-actin (actb) to be optimal for sample normalisation. In an experimental setting, chickens were inoculated with 500, 1500, or 4500 E. tenella oocysts and parasite replication and the impact of infection measured by i) qPCR analysis of DNA extracted from caecal tissues collected at five and eight days post-infection (dpi), ii) faecal oocyst counts (FOCs) on samples taken from six to eight dpi, and iii) lesion scoring on caeca collected post-mortem at five and eight dpi. Quantitative real-time PCR test results indicated a significant dose-dependent increase in parasite numbers among study groups for samples collected five dpi (i.e., prior to gametogony) (R(2)=0.994) (p<0.002) but not in those from day eight (after most oocyst shedding) (R(2)=0.006) (p>0.379). A strong dose-dependent increase in parasite replication and severity of infection was also revealed by FOC (R(2)=0.997) and lesion scoring. Importantly, qPCR offers substantial improvements for animal welfare via improved statistical power and reduced group sizes in experimental studies. The described qPCR method overcomes subjective limitations of coproscopic quantification, allows reproducible medium- to high-throughput examination of tissues, faeces, and oocysts, and is a valuable tool for determining the impact of Eimeria infections in both experimental and field settings.
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http://dx.doi.org/10.1016/j.parint.2015.06.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4534708PMC
October 2015

Genomic analysis of the causative agents of coccidiosis in domestic chickens.

Genome Res 2014 Oct 11;24(10):1676-85. Epub 2014 Jul 11.

Computational Bioscience Research Center, Biological Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Jeddah 23955-6900, Kingdom of Saudi Arabia;

Global production of chickens has trebled in the past two decades and they are now the most important source of dietary animal protein worldwide. Chickens are subject to many infectious diseases that reduce their performance and productivity. Coccidiosis, caused by apicomplexan protozoa of the genus Eimeria, is one of the most important poultry diseases. Understanding the biology of Eimeria parasites underpins development of new drugs and vaccines needed to improve global food security. We have produced annotated genome sequences of all seven species of Eimeria that infect domestic chickens, which reveal the full extent of previously described repeat-rich and repeat-poor regions and show that these parasites possess the most repeat-rich proteomes ever described. Furthermore, while no other apicomplexan has been found to possess retrotransposons, Eimeria is home to a family of chromoviruses. Analysis of Eimeria genes involved in basic biology and host-parasite interaction highlights adaptations to a relatively simple developmental life cycle and a complex array of co-expressed surface proteins involved in host cell binding.
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http://dx.doi.org/10.1101/gr.168955.113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4199364PMC
October 2014

Securing poultry production from the ever-present Eimeria challenge.

Trends Parasitol 2014 Jan 14;30(1):12-9. Epub 2013 Nov 14.

Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire, AL9 7TA, UK. Electronic address:

The intestinal disease coccidiosis, caused by protozoan parasites of the genus Eimeria, is one of the most important livestock diseases in the world. It has a high impact in the poultry industry where parasite transmission is favoured by high-density housing of large numbers of susceptible birds. Coccidiosis control in poultry is achieved by careful husbandry combined with in-feed anticoccidial drugs or vaccination with live parasites. However, outbreaks of coccidiosis still occur and subclinical infections, which significantly impact on productivity and food security, are common due to widespread drug resistance, high parasite prevalence, and environmental persistence. Herein, we review some recent approaches for the production of cheaper third generation vaccines, based on robust methods for identification of immunoprotective antigens and the use of transgenic Eimeria.
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http://dx.doi.org/10.1016/j.pt.2013.10.003DOI Listing
January 2014

An optimised protocol for molecular identification of Eimeria from chickens.

Vet Parasitol 2014 Jan 28;199(1-2):24-31. Epub 2013 Sep 28.

Division of Parasitology, Indian Veterinary Research Institute, Izatnagar 243 122, Uttar Pradesh, India.

Molecular approaches supporting identification of Eimeria parasites infecting chickens have been available for more than 20 years, although they have largely failed to replace traditional measures such as microscopy and pathology. Limitations of microscopy-led diagnostics, including a requirement for specialist parasitological expertise and low sample throughput, are yet to be outweighed by the difficulties associated with accessing genomic DNA from environmental Eimeria samples. A key step towards the use of Eimeria species-specific PCR as a sensitive and reproducible discriminatory tool for use in the field is the production of a standardised protocol that includes sample collection and DNA template preparation, as well as primer selection from the numerous PCR assays now published. Such a protocol will facilitate development of valuable epidemiological datasets which may be easily compared between studies and laboratories. The outcome of an optimisation process undertaken in laboratories in India and the UK is described here, identifying four steps. First, samples were collected into a 2% (w/v) potassium dichromate solution. Second, oocysts were enriched by flotation in saturated saline. Third, genomic DNA was extracted using a QIAamp DNA Stool mini kit protocol including a mechanical homogenisation step. Finally, nested PCR was carried out using previously published primers targeting the internal transcribed spacer region 1 (ITS-1). Alternative methods tested included sample processing in the presence of faecal material, DNA extraction using a traditional phenol/chloroform protocol, the use of SCAR multiplex PCR (one tube and two tube versions) and speciation using the morphometric tool COCCIMORPH for the first time with field samples.
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http://dx.doi.org/10.1016/j.vetpar.2013.09.026DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3858809PMC
January 2014