Evaluation of Next-Generation Amplicon Sequencing to Identify Eimeria spp. of Chickens

Eimeria of chickens: the changing face of an old foe

ABSTRACTEimeria are globally enzootic parasites that can cause coccidiosis in chickens. Until recently, remarkably little had changed over the last 40 years in the fundamental biology that underpins detection and control of Eimeria. Tools such as microscopy and lesion scoring remain central to diagnosis, and control still relies on routine supplementation of diets with anticoccidial drugs or application of live vaccines. However, refocusing on aspects of economics, molecular biology, and bacteriology that relate to coccidiosis has prompted considerable change in dogma. The cost of coccidiosis in chickens has been difficult to define, but updating models created in the 1990s suggested an annual cost to the global poultry industry of £10.4 billion in 2016, rising to a peak of £12.9 billion in 2022 under the influence of the COVID-19 pandemic and regional wars. Surveillance using genomic sequence-based diagnostics has suggested the presence of three new Eimeria species, supported by subsequent biological characterization of each line. Use of microbiome sequencing pipelines has revealed the breadth of impact Eimeria infection exerts on enteric microbiota, contributing to dysbiosis and deteriorating litter conditions. Enhanced understanding of Eimeria and the consequences of infection can be used to improve control and diagnosis with relevance to productivity and welfare, creating opportunities to optimize anticoccidial drug use.RESEARCH HIGHLIGHTSThe cost of coccidiosis in chickens fluctuates considerably, peaking in 2022.Three new Eimeria species can infect chickens and escape current vaccines.Eimeria infection exerts wide-ranging effects on enteric microbiota.

Morphological and molecular characterization of a pure isolate of Eimeria lata, identified for the first time in domestic chickens in Brazil

Coccidiosis of domestic chickens is caused by seven Eimeria species, in addition to three recently proposed species: Eimeria lata, Eimeria nagambie, and Eimeria zaria. This study reports the first identification of E. lata in domestic chickens in Brazil, the successful establishment of a pure E. lata isolate, and its morphological and molecular analyses. Fecal samples were collected from six extensive production systems in the state of São Paulo, Brazil, and screened for the 10 Eimeria species of domestic chickens through species-specific PCRs. To obtain E. lata oocysts, a mixture of oocysts from various Eimeria species was sequentially administered to commercial broiler chickens vaccinated against coccidiosis. Subsequently, a pure isolate of E. lata was obtained by micromanipulation and propagated in chickens. Eimeria lata oocysts were further subjected to morphological and molecular characterization. In conclusion, these findings constitute the first documentation of E. lata in domestic chickens in Brazil. The Brazilian E. lata isolate, designated BR-AMC, exhibited molecular and morphological characteristics similar to those of E. lata isolates from other countries.

Identification of Eimeria spp. in domestic chickens raised in alternative poultry production systems in the State of São Paulo, Brazil

The objective of this study was to identify Eimeria spp. in alternative poultry production systems (APPS) in the State of São Paulo, Brazil. Fecal samples (168) and DNA extracted from fecal samples obtained in APPS located in different Municipalities in the State of São Paulo (93) were examined by microscopy or genera-specific PCR (ITS-1 locus). Samples positive for Eimeria spp. were examined using Eimeria lata, Eimeria nagambie, and Eimeria zaria species-specific PCR protocols (ITS-2 locus) and another E. lata-specific PCR (candidate IMP1 genomic locus) followed by molecular cloning (E. lata and E. zaria ITS-2 amplicons) and genetic sequencing. All positive DNA samples were also submitted to genera-specific nested PCR (18S rRNA gene) followed by next-generation sequencing to identify Eimeria spp. Eimeria nagambie, E. zaria, and Eimeria sp. were identified by ITS2-targeted species-specific PCRs and genetic sequencing. Next-generation sequencing identified, in order of prevalence: E. nagambie; Eimeria acervulina; Eimeria mivati; Eimeria praecox; Eimeria brunetti; Eimeria mitis; Eimeria sp.; Eimeria maxima; E. zaria, and Eimeria necatrix/tenella. Our results confirmed, for the first time in Brazil, the identification of E. nagambie, E. zaria, and Eimeria spp. ITS-2 and 18S rRNA gene sequences not yet described in Brazil.

First detection and characterisation of Eimeria zaria in European chickens

The global poultry industry has experienced dramatic growth in recent decades, increasing the significance of pathogens of chickens. Protozoan parasites of the genus Eimeria can cause the disease coccidiosis, compromising animal health and welfare, and incurring significant annual costs. Seven Eimeria species have long been recognised to infect chickens, supplemented by three new candidate species first reported from Australia in 2007/8. Named Eimeria lata, Eimeria nagambie and Eimeria zaria, one or more of these new species have been reported in Australia, several countries in sub-Saharan Africa, India, Venezuela, and most recently the United States of America, but none have been detected in Europe. Here, a panel of 56 unvaccinated broiler chicken farms were sampled in the final week of production from France, Greece, Italy, the Netherlands, the Republic of Ireland, and the United Kingdom to assess the occurrence of all ten Eimeria species using specific polymerase chain reaction (PCR). Overall, 39 of 56 (69.6%) farms were found to host at least one species. Eimeria acervulina, E. tenella, and E. maxima were most common, with E. mitis and E. praecox also widespread. Eimeria necatrix was detected on one farm in France, while E. brunetti was not detected. Eimeria zaria was detected for the first time in Europe, appearing in Greece and Italy (one occurrence each). New primers were designed to confirm detection of E. zaria and provide template for phylogenetic comparison with the reference isolate from Australia. Detection of E. zaria in Europe reinforces the importance of integrated control for coccidiosis given the lack of protection induced by current anticoccidial vaccines.

Xylanase and beta-glucanase improve performance parameters and footpad dermatitis and modulate intestinal microbiota in broilers under an Eimeria challenge

Coccidiosis is an enteric disease of poultry worldwide that compromises gut health and growth performance. The current research investigated the effects of 2 doses of a multienzyme preparation on broilers' performance, gut health, and footpad dermatitis (FPD) under an Eimeria challenge. A total of 512 mixed-sex day-old chicks (Cobb 500) were randomly allocated to 4 treatments of 8 replicates. Treatments were: 1) nonchallenged control (NC); 2) NC + Eimeria challenge (CC); 3) CC + recommended level of xylanase and glucanase (XG, 100 g/t feed [on top]); 4) CC + double XG (2XG, 200 g/t feed). Eimeria spp. vaccine strains were gavaged on d 9 to induce coccidiosis in chickens. Performance parameters were evaluated during starter, grower, and finisher phases, and 4 birds per pen were euthanized on d 16 for sampling, FPD was scored on d 35, and litter moisture was analyzed on d 17 and 35. The data were analyzed using 1-way ANOVA with Tukey's test to separate means, and Kruskal-Wallis test was used for non-normally distributed parameters. The results showed that the Eimeria challenge was successful based on reduced weight gain and feed intake during grower phase, and higher FITC-d concentration, lesion score (female), and oocyst counts (d 14) in CC group compared to N.C. group, while XG and 2XG increased (P < 0.001) weight gain and improved FCR compared to CC and NC groups during finisher phase. The addition of X.G. and 2XG decreased litter moisture (P = 0.003) and FPD (P < 0.001) in challenged broilers compared to the N.C. group (d 35). Supplementing XG and 2XG reestablished the population of Lactobacillus in the cecum of challenged birds to an intermediate level between the NC and CC groups (P > 0.05). The inclusion of XG tended to increase the expression of Junctional adhesion molecule 2 (JAM2), which was not different from CC and NC groups (P > 0.05). In conclusion, the combination of xylanase and glucanase (Natugrain TS) improved the performance and modulated jejunal microbiota of broilers under mild Eimeria challenge.

Impacts of Eimeria coinfection on growth performance, intestinal health and immune responses of broiler chickens

Coccidiosis caused by Eimeria is one of the most severe chicken diseases and imposes huge economic losses to the poultry industry globally. Multi-Eimeria species coinfections are common with the most prevalent combination being mixtures of Eimeria acervulina and Eimeria tenella. Although detrimental impacts of either E. acervulina or E. tenella on chicken health are well recognized, no information is available regarding their coinfection effects so far. This study was designed to investigate the influence of coinfection with E. acervulina and E. tenella on broiler chickens. 144 one-day-old broiler chickens within each of trials (trial I or II) were divided into four groups, namely, control group (CG), E. acervulina infection group (EAIG), E. tenella infection group (ETIG) and dual (E. acervulina and E. tenella) infection group (DIG). Then, chickens were measured for weight loss, lesion scores, oocyst outputs, histological changes and expressions of pro-inflammatory (interleukin [IL]-6, IL-8 and IL-18), regulatory (IL-10 and IL-22) cytokines and Toll-like receptors (TLR; TLR2 and TLR4) as well as intestinal barrier (mucin 2 [MUC2] and fattey acid-bingding proteins 2 and 6 [FABP2 and FABP6])- and tight junction (TJ; zonula occluden-1 [ZO-1], occludin [OCLN], and claudins 1 and 5 [CLDN1 and CLDN5])-related proteins at 3, 5, 7, 10, 14 and 21 days post-infection, respectively. Our results consistently showed that although ETIG and DIG exhibited a higher level of weight loss and a more amount of oocyst excretion than EAIG, DIG had lighter lesions than EAIG in the early phase because of coinfection with E. tenella. A higher (P < 0.05) ratio of duodenal villous height to crypt depth was also observed in DIG than EAIG. Moreover, histological changes in the duodenum and cecum varied by single and dual Eimeria infections. Expressions of the intestinal barrier- and TJ-related genes of EAIG, ETIG and DIG were significantly (P < 0.05) upregulated but their levels exhibited differential changes among infected chickens. Similarly, the infected chickens showed significant (P < 0.05) inflammatory responses and higher (P < 0.05) expressions of TLRs in the intestines in comparison to CG. These results presented a comprehensive physiological, pathological and immunological characterization of E. acervulina and E. tenella coinfection in broiler chickens and also shed insights into pathogenesis of multi-coccidia coinfections.

Exploring the genetic diversity of Eimeria acervulina: A polymerase chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) approach

Eimeria, protozoan parasites that can cause the disease coccidiosis, pose a persistent challenge to poultry production and welfare. Control is commonly achieved using good husbandry supplemented with routine chemoprophylaxis and/or live parasite vaccination, although widespread drug resistance and challenges to vaccine supply or cost can prove limiting. Extensive effort has been applied to develop subunit anticoccidial vaccines as scalable, cost-effective alternatives, but translation to the field will require a robust understanding of parasite diversity. Using a new Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) panel we begin to describe the genetic diversity of Eimeria acervulina populations in Africa and Europe. PCR-RFLP genotyping E. acervulina populations sampled from commercial broiler and layer chickens reared in Nigeria or the United Kingdom (UK) and Republic of Ireland (RoI) revealed comparable levels of haplotype diversity, in direct contrast to previous descriptions from the close relative E. tenella. Here, 25 distinct PCR-RFLP haplotypes were detected from a panel of 42 E. acervulina samples, including 0.7 and 0.5 haplotypes per sample in Nigeria (n = 20) and the UK/RoI (n = 14), respectively. All but six haplotypes were found to be country-specific. The PCR-RFLP markers immune mapped protein 1 (IMP1) and heat shock protein 90 (HSP90) were most informative for Nigerian E. acervulina, while microneme protein 3 (MIC3) and HSP90 were most informative in UK/RoI populations. High haplotype diversity within E. acervulina populations may indicate frequent genetic exchange and potential for rapid dissemination of genetic material associated with escape from selective barriers such as anticoccidial drugs and future subunit vaccines.

Amplicon sequencing allows differential quantification of closely related parasite species: an example from rodent Coccidia (Eimeria)

BACKGROUND

Quantifying infection intensity is a common goal in parasitological studies. We have previously shown that the amount of parasite DNA in faecal samples can be a biologically meaningful measure of infection intensity, even if it does not agree well with complementary counts of transmission stages (oocysts in the case of Coccidia). Parasite DNA can be quantified at relatively high throughput using quantitative polymerase chain reaction (qPCR), but amplification needs a high specificity and does not simultaneously distinguish between parasite species. Counting of amplified sequence variants (ASVs) from high-throughput marker gene sequencing using a relatively universal primer pair has the potential to distinguish between closely related co-infecting taxa and to uncover the community diversity, thus being both more specific and more open-ended.

METHODS

We here compare qPCR to the sequencing-based amplification using standard PCR and a microfluidics-based PCR to quantify the unicellular parasite Eimeria in experimentally infected mice. We use multiple amplicons to differentially quantify Eimeria spp. in a natural house mouse population.

RESULTS

We show that sequencing-based quantification has high accuracy. Using a combination of phylogenetic analysis and the co-occurrence network, we distinguish three Eimeria species in naturally infected mice based on multiple marker regions and genes. We investigate geographical and host-related effects on Eimeria spp. community composition and find, as expected, prevalence to be largely explained by sampling locality (farm). Controlling for this effect, the novel approach allowed us to find body condition of mice to be negatively associated with Eimeria spp. abundance.

CONCLUSIONS

We conclude that amplicon sequencing provides the underused potential for species distinction and simultaneous quantification of parasites in faecal material. The method allowed us to detect a negative effect of Eimeria infection on the body condition of mice in the natural environment.

What Do We Know about Surface Proteins of Chicken Parasites Eimeria?

Poultry is the first source of animal protein for human consumption. In a changing world, this sector is facing new challenges, such as a projected increase in demand, higher standards of food quality and safety, and reduction of environmental impact. Chicken coccidiosis is a highly widespread enteric disease caused by Eimeria spp. which causes significant economic losses to the poultry industry worldwide; however, the impact on family poultry holders or backyard production-which plays a key role in food security in small communities and involves mainly rural women-has been little explored. Coccidiosis disease is controlled by good husbandry measures, chemoprophylaxis, and/or live vaccination. The first live vaccines against chicken coccidiosis were developed in the 1950s; however, after more than seven decades, none has reached the market. Current limitations on their use have led to research in next-generation vaccines based on recombinant or live-vectored vaccines. Next-generation vaccines are required to control this complex parasitic disease, and for this purpose, protective antigens need to be identified. In this review, we have scrutinised surface proteins identified so far in Eimeria spp. affecting chickens. Most of these surface proteins are anchored to the parasite membrane by a glycosylphosphatidylinositol (GPI) molecule. The biosynthesis of GPIs, as well as the role of currently identified surface proteins and interest as vaccine candidates has been summarised. The potential role of surface proteins in drug resistance and immune escape and how these could limit the efficacy of control strategies was also discussed.

Comprehensive molecular characterization of complete mitogenome assemblies of 33 Eimeria isolates infecting domestic chickens

BACKGROUND

Coccidiosis caused by Eimeria is one of the most severe chicken diseases and poses a great economic threat to the poultry industry. Understanding the evolutionary biology of chicken Eimeria parasites underpins development of new interactions toward the improved prevention and control of this poultry disease.

METHODS

We presented an evolutionary blueprint of chicken coccidia by genetically characterizing complete mitogenome assemblies of 33 isolates representing all seven known Eimeria species infecting chickens in China. Further genome- and gene-level phylogenies were also achieved to better understand the evolutionary relationships of these chicken Eimeria at the species level.

RESULTS

33 mitogenomes of chicken eimerian parasites ranged from 6148 bp to 6480 bp in size and encoded typical mitochondrial compositions of apicomplexan parasites including three protein-coding genes (PCGs), seven fragmented small subunit (SSU) and 12/13 fragmented large subunit (LSU) rRNAs. Comparative genomics provided an evolutionary scenario for the genetic diversity of PCGs-cytochrome c oxidase subunits 1 and 3 (cox1 and cox3) and cytochrome b (cytb); all were under purifying selection with cox1 and cox3 being the lowest and highest evolutionary rates, respectively. Genome-wide phylogenies classified the 33 Eimeria isolates into seven subgroups, and furthermore Eimeria tenella and Eimeria necatrix were determined to be more closely related to each other than to the other eight congenic species. Single/concatenated mitochondrial protein gene-based phylogenies supported cox1 as the genetic marker for evolutionary and phylogenetic studies for avain coccidia.

CONCLUSIONS

To our knowledge, these are the first population-level mitogenomic data on the genus Eimeria, and its comprehensive molecular characterization provides valuable resources for systematic, population genetic and evolutionary biological studies of apicomplexan parasites in poultry.

Next-generation sequencing amplicon analysis of the genetic diversity of Eimeria populations in livestock and wildlife samples from Australia

Eimeria is an important coccidian enteric parasite that infects a wide range of hosts and can cause substantial economic losses in the poultry and livestock industries. It is common for multiple Eimeria species to infect individual hosts, and this can make species identification difficult due to morphological similarities between species and mixed chromatograms when using Sanger sequencing. Relatively few studies have applied next-generation amplicon sequencing (NGS) to determining the genetic diversity of Eimeria species in different hosts. The present study screened 408 faecal samples from a range of hosts including livestock and wildlife using a previously developed quantitative polymerase chain reaction (qPCR) at the 18S locus and conducted amplicon NGS on the positives using a ~ 455-bp fragment of the 18S locus. A total of 41 positives (10.1%) were identified by qPCR from various hosts and NGS was successful for 38 of these positives. Fifteen Eimeria species and three genotypes were detected by NGS: E. ferrisi, E. kanyana, E. potoroi, E. quokka, E. setonicis, E. trichosuri, E. reichenowi, E. angustus, E. ahsata, E. auburnensis, E. bovis, E. brasiliensis, E. christenseni, E. crandallis, E. ovinoidalis, Eimeria sp. (JF419345), Eimeria sp. (JF419349) and Eimeria sp. (JF419351). Mixed infections were detected in 55.3% (21/38) of positive samples. The most striking finding was the identification of the same species in different hosts. This could be due to contamination and/or mechanical transmission or may provide support for previous studies suggesting that Eimeria species can infect not just closely related hosts but different genera and further research is required. This is also the first study to audit Eimeria populations in livestock (sheep and cattle) by NGS and could be applied in the future to determine the extent of pathogenic species and outcomes of Eimeria control strategies.

Multilocus Sequence Typing of Eimeria maxima in Commercial Broiler Flocks

About 35% of all broiler flocks in the United States receive an anticoccidial vaccine, but it is not possible to easily differentiate Eimeria vaccine strains from Eimeria field isolates. Being able to do that would allow using vaccines in a more targeted way. The objective of this study was to collect Eimeria maxima isolates from broiler flocks that received anticoccidial feed additives and flocks that had been vaccinated against coccidia and then test them with a multilocus sequencing typing (MLST) scheme developed for this study. Fecal samples were obtained from commercial broiler flocks in Alabama and Tennessee. Oocyst counts in samples tended to be lower in flocks receiving anticoccidial feed additives and higher in vaccinated flocks. Selected samples were screened for presence of E. maxima by quantitative PCR, and Eimeria spp. composition was investigated by next-generation amplicon sequencing (NGAS) in 37 E. maxima positive samples. Other detected Eimeria spp. besides E. maxima were Eimeria acervulina in 35 samples, Eimeria praecox in 23 samples, Eimeria mitis or Eimeria mivati in 17 samples, and Eimeria necatrix or Eimeria tenella in 10 samples. Six partial E. maxima genes (dnaJ domain containing protein, 70-kDa heat shock protein, prolyl endopeptidase, regulator of chromosome condensation domain containing protein, serine carboxypeptidase, and vacuolar proton-translocating ATPase subunit) of 46 samples were sequenced. The MLST scheme was able to differentiate two vaccines from each other. Three of 17 samples from vaccinated flocks differed from the vaccine used in the flock, while 16 of 29 samples from unvaccinated flocks differed from the vaccine. However, there was also a large number of low-quality, ambiguous chromatograms and negative PCRs for the selected genes. If and when more advanced, possibly next-generation sequencing-based methods will be developed, the genes should be considered as targets.

A multiepitope vaccine encoding four Eimeria epitopes with PLGA nanospheres: a novel vaccine candidate against coccidiosis in laying chickens

With a worldwide distribution, Eimeria spp. could result in serious economic losses to the poultry industry. Due to drug resistance and residues, there are no ideal drugs and vaccines against Eimeria spp. in food animals. In the current study, a bioinformatics approach was employed to design a multiepitope antigen, named NSLC protein, encoding antigenic epitopes of E. necatrix NA4, E. tenella SAG1, E. acervulina LDH, and E. maxima CDPK. Thereafter, the protective immunity of NSLC protein along with five adjuvants and two nanospheres in laying chickens was evaluated. Based on the humoral immunity, cellular immunity, oocyst burden, and the coefficient of growth, the optimum adjuvant was evaluated. Furthermore, the optimum immune route and dosage were also investigated according to the oocyst burden and coefficient of growth. Accompanied by promoted secretion of antibodies and enhanced CD4⁺ and CD8⁺ T lymphocyte proportions, NSLC proteins entrapped in PLGA nanospheres were more effective in stimulating protective immunity than other adjuvants or nanospheres, indicating that PLGA nanospheres were the optimum adjuvant for NSLC protein. In addition, a significantly inhibited oocyst burden and growth coefficient promotion were also observed in animals vaccinated with NSLC proteins entrapped in PLGA nanospheres, indicating that the optimum adjuvant for NSLC proteins was PLGA nanospheres. The results also suggested that the intramucosal route with PLGA nanospheres containing 300 μg of NSLC protein was the most efficient approach to induce protective immunity against the four Eimeria species. Collectively, PLGA nanospheres loaded with NSLC antigens are potential vaccine candidates against avian coccidiosis.

Chicken Coccidiosis: From the Parasite Lifecycle to Control of the Disease

The poultry industry is one of the main providers of protein for the world's population, but it faces great challenges including coccidiosis, one of the diseases with the most impact on productive performance. Coccidiosis is caused by protozoan parasites of the genus Eimeria, which are a group of monoxenous obligate intracellular parasites. Seven species of this genus can affect chickens (Gallus gallus), each with different pathogenic characteristics and targeting a specific intestinal location. Eimeria alters the function of the intestinal tract, generating deficiencies in the absorption of nutrients and lowering productive performance, leading to economic losses. The objective of this manuscript is to review basic concepts of coccidiosis, the different Eimeria species that infect chickens, their life cycle, and the most sustainable and holistic methods available to control the disease.

Controlling the causative agents of coccidiosis in domestic chickens; an eye on the past and considerations for the future

Coccidiosis is a potentially severe enteritis caused by species of obligate intracellular parasites of the genus Eimeria. These parasites cause significant economic losses to the poultry industry, predominantly due to compromised efficiency of production as well as the cost of control. These losses were recently estimated to cost chicken producers approximately £10.4 billion worldwide annually. High levels of Eimeria infection cause clinical coccidiosis which is a significant threat to poultry welfare, and a pre-disposing contributory factor for necrotic enteritis. Control of Eimeria parasites and coccidiosis is therefore an important endeavour; multiple approaches have been developed and these are often deployed together. This review summarises current trends in strategies for control of Eimeria, focusing on three main areas: good husbandry, chemoprophylaxis and vaccination. There is currently no "perfect solution" and there are advantages and limitations to all existing methods. Therefore, the aim of this review is to present current control strategies and suggest how these may develop in the future.

Exploiting digital droplet PCR and Next Generation Sequencing technologies to determine the relative abundance of individual Eimeria species in a DNA sample

DNA-based diagnostic assays for detecting infections with Eimeria species have been limited to providing identification and presence/absence data for samples containing oocysts. Modern technologies that generate quantitative data, such as droplet digital PCR (ddPCR) and Next Generation Sequencing (NGS), utilize a relatively short amplicon size containing sufficient species-specific variation for reliable species level identification. Targeting the cytochrome c oxidase subunit III gene in the mitochondrial genome, we established protocols using these technologies to determine the relative abundance of the number of copies/μL of Eimeria species in a sample. Samples from chickens of known and unknown Eimeria species composition were analyzed to determine the suitability of these technologies as diagnostic assays. All technologies demonstrated robust capability of identifying and quantifying the Eimeria species in samples. The new quantitative assays described herein will produce invaluable detail of Eimeria species infections for an array of situations in commercial chicken production systems, enabling further characterization of the disease profile and allowing for the development or enhancement of new intervention strategies.

Spotlight on avian pathology: Eimeria and the disease coccidiosis

Coccidiosis, caused by Eimeria species parasites, remains a major threat to poultry production, undermining economic performance and compromising welfare. The recent characterization of three new Eimeria species that infect chickens has highlighted that many gaps remain in our knowledge of the biology and epidemiology of these parasites. Concerns about the use of anticoccidial drugs, widespread parasite drug resistance, the need for vaccines that can be used across broiler as well as layer and breeder sectors, and consumer preferences for "clean" farming, all point to the need for novel control strategies. New research tools including vaccine delivery vectors, high throughput sequencing, parasite transgenesis and sensitive molecular assays that can accurately assess parasite development in vitro and in vivo are all proving helpful in the ongoing quest for improved cost-effective, scalable strategies for future control of coccidiosis.

Prevalence of Select Intestinal Parasites in Alabama Backyard Poultry Flocks

Simple Summary

As biosecurity is generally low in backyard chicken flocks, infections with various pathogens are common. This puts other poultry nearby, including commercial flocks, at risk. Some chicken pathogens can also infect humans and cause disease. In this study, backyard poultry flocks were tested for parasites. Eighty-four fecal samples, 82 from chickens and two from turkeys, from 64 backyard flocks throughout the state of Alabama were collected in the summers of 2017 and 2018. The most frequently observed parasites were coccidia, unicellular parasites capable of causing diarrhea. Eggs of various roundworms were observed in 20.3–26.6% of the flocks. These parasites were usually present in low numbers only. Other detected parasites were the flagellates Histomonas meleagridis and Tetratrichomonas gallinarum in 4.7% and 18.8% of flocks. Both can cause severe disease in poultry. Detected parasites that can cause disease in humans were Cryptosporidium spp. in 18.8% of the flocks and Blastocystis spp. in 87.5% of the flocks. The results will help to provide information that can be used to design outreach programs to improve the health and wellbeing of birds in backyard flocks.

Abstract

Keeping chickens as backyard pets has become increasingly popular in the United States in recent years. However, biosecurity is generally low in backyard flocks. As a consequence, they can serve as reservoirs for various pathogens that pose a risk for commercial poultry or human health. Eighty-four fecal samples, 82 from chickens and two from turkeys, from 64 backyard flocks throughout the state of Alabama were collected in the summers of 2017 and 2018. Coccidia oocysts were seen in 64.1% of flocks with oocyst counts in most samples below 10,000 oocysts per gram. Eggs of Ascaridia spp. or Heterakis gallinarum were observed in 20.3% of the flocks, and eggs of Capillaria spp. in 26.6% of the flocks. Egg counts were low, rarely exceeding 1000 eggs per gram. DNA extracted directly from fecal samples was investigated by PCR for other relevant parasites. The results showed that 4.7% of flocks were positive for Histomonas meleagridis, 18.8% of flocks for Tetratrichomonas gallinarum, 18.8% of flocks for Cryptosporidium spp. and 87.5% of flocks for Blastocystis spp. The results will help to provide information that can be used to design outreach programs to improve health and wellbeing of birds in backyard flocks.

Genetic and biological characterisation of three cryptic Eimeria operational taxonomic units that infect chickens (Gallus gallus domesticus)

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Biology and genetics suggest cryptic Eimeria Operational Taxonomic Units (OTUs) from chickens are new species.

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New Eimeria spp. that infect chickens are pathogenic and require control.

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Anticoccidial vaccination of chickens does not control three new Eimeria spp.

More than 68 billion chickens were produced globally in 2018, emphasising their major contribution to the production of protein for human consumption and the importance of their pathogens. Protozoan Eimeria spp. are the most economically significant parasites of chickens, incurring global costs of more than UK £10.4 billion per annum. Seven Eimeria spp. have long been recognised to infect chickens, with three additional cryptic operational taxonomic units (OTUs) first described more than 10 years ago. As the world’s farmers attempt to reduce reliance on routine use of antimicrobials in livestock production, replacing drugs that target a wide range of microbes with precise species- and sometimes strain-specific vaccines, the breakthrough of cryptic genetic types can pose serious problems. Consideration of biological characteristics including oocyst morphology, pathology caused during infection and pre-patent periods, combined with gene-coding sequences predicted from draft genome sequence assemblies, suggest that all three of these cryptic Eimeria OTUs possess sufficient genetic and biological diversity to be considered as new and distinct species. The ability of these OTUs to compromise chicken bodyweight gain and escape immunity induced by current commercially available anticoccidial vaccines indicates that they could pose a notable threat to chicken health, welfare, and productivity. We suggest the names Eimeria lata n. sp., Eimeria nagambie n. sp. and Eimeria zaria n. sp. for OTUs x, y and z, respectively, reflecting their appearance (x) or the origins of the first isolates of these novel species (y, z).

A survey of coccidia and nematodes in pastured poultry in the state of Georgia

The aim of this study was to evaluate and quantify the parasitological challenge in pastured poultry production in the state of Georgia. Over the course of one year, fecal samples from six turkey flocks, ten broiler flocks and 13 layer flocks were collected on a pastured farm in two-week intervals to determine counts of Eimeria oocysts and nematode eggs. Average coccidia counts were 10,198 oocysts per gram of feces (OPG) in broiler flocks, 1,470 OPG in layer flocks and 695 OPG in turkey flocks. The means in broiler and turkey flocks were higher at their first week on pasture. Counts in broilers and layers were significantly higher in spring than in winter and summer. Coccidia counts in broilers were lower than published numbers in conventionally reared poultry, indicating the rotation system of the pastures might effectively reduce the infection pressure. Next-generation sequencing of PCR products showed the presence of most described Eimeria spp. in broilers, layers, and turkeys. In addition, Operational Taxonomic Units (OTUs) x, y and z were found. The frequency of species was similar for broilers and layers, with the exception that Eimeria praecox and OTU z were more common in layers. In layer flocks, the average count of roundworm eggs per gram of feces (EPG) was 509 EPG with 80% of the samples being positive. The mean counts had no clear pattern related to age. There was an increase of EPG with the increase of temperatures during spring and summer with the peak at mid-fall. Worm eggs from laying hens were identified as A. galli. The seasonal differences suggest that higher temperatures might result in an increase of egg survival and sporulation in the environment.

Restoration of anticoccidial sensitivity to a commercial broiler chicken facility in Canada

Increasing resistance of Eimeria species to anticoccidial medications is an issue in the broiler chicken industry. Using drug-sensitive strains in live-coccidiosis vaccines has been shown to improve anticoccidial effectiveness in US-based broiler production. In Canada, litter is removed between flocks, which differ from the US industry practice. Thus, we investigated the use of drug-sensitive vaccine strains in a Canadian broiler production facility with suspected anticoccidial resistance. Weekly fecal samples were collected from flocks before, during, and after vaccine seeding to determine oocyst shedding patterns; following the vaccine seeding, OPG counts from similar aged birds were lower than flocks before live-coccidiosis vaccine use. Eimeria species isolates, collected before and after vaccine seeding, were used in 2 anticoccidial sensitivity tests to evaluate their susceptibility to commercially available anticoccidial medications; a low-dose challenge to define parasite replication, and a high-dose challenge to monitor broiler performance. In both experiments, isolates collected after seeding were more susceptible to almost every anticoccidial medication evaluated compared with the isolates collected before seeding. These results demonstrate an improvement in sensitivity to many anticoccidials after the use of live-coccidiosis vaccines at this facility. However, the regulated removal of litter at the end of each flock required under Canadian broiler chicken production management rules could limit the establishment of vaccine-strain Eimeria species in broiler facilities and could shorten the longevity of improved drug sensitivity observed in this study.

Exploring Eimeria Genomes to Understand Population Biology: Recent Progress and Future Opportunities

Eimeria, protozoan parasites from the phylum Apicomplexa, can cause the enteric disease coccidiosis in all farmed animals. Coccidiosis is commonly considered to be most significant in poultry; due in part to the vast number of chickens produced in the World each year, their short generation time, and the narrow profit margins associated with their production. Control of Eimeria has long been dominated by routine chemoprophylaxis, but has been supplemented or replaced by live parasite vaccination in a minority of production sectors. However, public and legislative demands for reduced drug use in food production is now driving dramatic change, replacing reliance on relatively indiscriminate anticoccidial drugs with vaccines that are Eimeria species-, and in some examples, strain-specific. Unfortunately, the consequences of deleterious selection on Eimeria population structure and genome evolution incurred by exposure to anticoccidial drugs or vaccines are unclear. Genome sequence assemblies were published in 2014 for all seven Eimeria species that infect chickens, stimulating the first population genetics studies for these economically important parasites. Here, we review current knowledge of eimerian genomes and highlight challenges posed by the discovery of new, genetically cryptic Eimeria operational taxonomic units (OTUs) circulating in chicken populations. As sequencing technologies evolve understanding of eimerian genomes will improve, with notable utility for studies of Eimeria biology, diversity and opportunities for control.