Within-year variation in infection is a ubiquitous feature of natural populations, but is determined by a complex interplay of environmental, parasitological and host factors. At the same time, co-infection is the norm in the wild. Longitudinal dynamics of co-infecting parasites may therefore be further complicated by covariation across multiple parasites. Here, we used fecal parasite egg and oocyst counts collected repeatedly from individually marked wild Soay sheep to investigate seasonal dynamics of six gastrointestinal parasite groups. Prevalence and abundance tended to be higher in spring and summer, and abundance was higher in lambs compared to adults. We found that within-year variation in highly prevalent strongyle nematode counts was dependent on adult reproductive status, where reproductive ewes had distinct dynamics compared to males and barren ewes. For similarly prevalent coccidia we found an overall peak in oocyst counts in spring but no differences among males, barren and pregnant ewes. Using multivariate mixed-effects models, we further show that apparent positive correlation between strongyle and coccidia counts was driven by short-term within-individual changes in both counts rather than long-term among-individual covariation. Overall, these results demonstrate that seasonality varies across demographic and parasite groups and highlight the value of investigating co-infection dynamics over time.

Coccidiosis caused by Eimeria species is a well-recognized disease of livestock. Enteric Eimeria infections are common, but disease usually only manifests when infection intensity is abnormally high. Campylobacter species are important zoonotic enteric bacterial pathogens for which livestock are important reservoir hosts. The diversity and epidemiology of ovine Eimeria and Campylobacter infections on two farms in north-western England were explored through a 24-month survey of shedding in sheep feces. Most animals were infected with at least one of 10 different Eimeria species, among which E. bakuensis and E. ovinoidalis were most common. An animal's age and the season of sampling were associated with the probability and intensity of Eimeria infection. Season of sampling was also associated with the probability of Campylobacter infection. Interestingly, higher intensities of Eimeria infections were significantly more common in animals not co-infected with Campylobacter. We explored the determinants of E. bakuensis and E. ovinoidalis infections, observing that being infected with either significantly increased the likelihood of infection with the other. The prevalence of E. ovinoidalis infections was significantly lower in sheep infected with Campylobacter. Recognition that co-infectors shape the dynamics of parasite infection is relevant to the design of effective infection control programmes.

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.

Helminth and protozoan infections are responsible for important diseases in grazing sheep, which can be especially threatening in an autochthonous breed at risk of extinction like the Churra Galega Mirandesa Portuguese sheep breed. The aim of the present study was to determine the diversity, prevalence and burden of gastrointestinal parasites in these sheep and to assess the effects of deworming practices, cohabiting animals on the farm and feed management. Coprological qualitative and quantitative analysis (flotation, natural sedimentation and McMaster method) were used to identify and quantify gastrointestinal parasites and a questionnaire was designed and applied. A total of 512 faecal samples were collected from 49 flocks, and 49 replies to the questionnaire were received. Parasites were identified in 100% of the flocks, and in 97% of the samples. The genera or species that have been morphologically identified were: strongyle-type, Nematodirus spp., Skrjabinema spp., Moniezia expansa, Moniezia benedeni, Trichuris spp., Capillaria spp., Eimeria spp., Dicrocoelium spp. and Fasciola hepatica. This is the first report in Portugal of Skrjabinema spp. The burden of parasites’ oocysts and eggs per gram in faecal samples ranged, respectively, from 50 to 17,550 for Eimeria spp., and from 50 to 6250 for strongyle-type eggs. Factors affecting parasitic infections were evaluated using a multivariate logistic regression. Grazing time and a lack of anthelmintic treatment were positively associated with Nematodirus spp. infection. This study showed that there is a high prevalence and diversity of gastrointestinal parasites in the Churra Galega Mirandesa sheep breed.

Coccidiosis is an antagonistic poultry disease which negatively impacts animal welfare and productivity. The disease is caused by an obligate, intracellular protozoon known as Eimeria. Several Eimeria species known to infect chickens have been well documented. However, recent studies have elucidated the emergence of three novel genetic variants or operational taxonomic units (OTUs). The discovery of OTUx, OTUy and OTUz complicates the identification and diagnosis of coccidiosis. OTUs are clusters of unknown or uncultivated organisms that are grouped according to a similarity in DNA sequence to a set of specific gene markers. OTUs have been reported in the Earth's Southern Hemisphere, including Australia, Venezuela, India, Zambia, Uganda, Tanzania, China and Ghana. Elucidating their impact on the poultry industry is fundamental in preventing anticoccidial resistance and to access the potential of OTUs as vaccine candidates to provide cross-protection against similar Eimeria species. The identification of OTUs further decreases the risk of false negative coccidial diagnosis. Therefore, this article reviews the importance and risk imposed by OTUs, coupled with their prevalence and geographical distribution in chickens globally.

Dendritic cells (DC) are central regulators of immune responses and professional antigen-presenting cells (APCs) with the unique ability to induce both innate immune responses and a highly specific acquired immunity. DC communicates through chemical and mechanical signals in the initiation and maintenance of immune responses. DC forms immunological synapses with T-cells thus pulling T-cells strings and leading to activation of T-cells. Owing to their properties, DC are often called ‘nature's adjuvants’ and thus have become an important component of any vaccination strategy. Coccidiosis is a major intestinal disease caused by Eimeria spp., affecting economically valuable livestock animals such as chickens and turkeys. Economic losses are associated with decreased productivity in afflicted poultry. Vaccination strategies involving DC have been developed owing to the special properties of these cells in coordinating innate and adaptive immune responses. Vaccination of chickens with exosomes isolated from DC containing parasite antigens (Ags) represents a promising alternative strategy to control avian coccidiosis. In recent years, emergence of new chicken DC has opened a new horizon for the development of new vaccines and DC derived vaccine could be a possible strategy to control coccidiosis in field. This review summarises the current state of knowledge of DC and their specific functions in immunity against avian coccidiosis.

Domestication of chickens from the wild red jungle fowl and modernisation of the poultry industry has changed both poultry and their intestinal microbiome, specifically the eimerian-microbiome-host relationship. Eimeria spp. represent an enteric parasite that has a long co-evolutionary history with their hosts. These parasites have adapted to suit an environment in which chickens thrive and the chickens’ intestinal environment, including the changing host microbiome. This review will delve into the changes in eimerian-host interactions with wild red jungle fowl versus domesticated chickens. The changing nature and composition of the intestinal microbiota as it followed the red jungle fowl into domestication and the relationship of this evolving microbiota with coccidia will be explored. Better comprehension of the web of interactions among the evolving eimerian-microbiome-host relationship will allow for the responsible exploitation of these relationships to maximise poultry health and productivity.

The Apicomplexa is a phylum of parasitic protozoa, which includes the malaria parasite Plasmodium, amongst other species that can devastate human and animal health. The past decade has seen the release of genome sequences for many of the most important apicomplexan species, providing an excellent basis for improving our understanding of their biology. One of the key features of each genome is a unique set of large, variant gene families. Although closely related species share the same families, even different types of malaria parasite have distinct families. In some species they tend to be found at the ends of chromosomes, which may facilitate aspects of gene expression regulation and generation of sequence diversity. In others they are scattered apparently randomly across chromosomes. For some families there is evidence they are involved in antigenic variation, immune regulation and immune evasion. For others there are no known functions. Even where function is unknown these families are most often predicted to be exposed to the host, contain much sequence diversity and evolve rapidly. Based on these properties it is clear that they are at the forefront of host–parasite interactions. In this review I compare and contrast the genomic context, gene structure, gene expression, protein localization and function of these families across different species.

There has been growing interest in the development of natural methods of coccidiosis prophylaxis. Vaccination against coccidiosis with live oocysts is regarded as effective in the control of avian coccidiosis, but in some conditions, such as poor sanitary management or incorrect application of the vaccine, may lead to poorer performance, measured as reduced weight gain and feed efficiency, in comparison with prophylactically medicated birds. Such reports are the reason for widespread reluctance to use anticoccidial vaccine in broilers. This paper reviews broiler studies in which nutritional methods as performance and/or immune-supporting factor with regard to anticoccidial vaccination were investigated. The results of some of the studies presented in the article indicate that feed additives with immunostimulating properties, along with proper protein levels in the diet, may have a beneficial effect in cocci-vaccinated broilers.

Coccidiosis, a serious disease resulting from infection with parasitic protozoa of the genus Eimeria, causes significant economic losses to the poultry industry, where intensive rearing facilitates transmission of infectious oocysts via the fecal/oral route. Current control relies primarily on prophylactic drugs in feed but, whilst cost effective, the rise of drug resistance and public demands for residue-free meat has encouraged development of alternative control strategies. Chickens that recover from infection with Eimeria develop solid immunity that is directed against the early asexual stages of the parasite life cycle. This has allowed development of a number of vaccines that utilize deliberate infection with controlled doses of virulent oocysts or reproductively attenuated lines of Eimeria. The latter are immunogenic but non-pathogenic. The realization that both prophylactic drugs and attenuated vaccines control but do not eradicate infection with Eimeria encouraged development of a vaccine based upon maternal immunity. Laying hens exposed to Eimeria are able to transfer protective antibodies to hatchlings via egg yolks and these antibodies have been used to identify parasite proteins that are conserved across the genus. When delivered maternally, these provide an economical means of preventing coccidiosis, offering immediate protection to newly hatched chicks.

Eimeria is a common genus of apicomplexan parasites that infect diverse vertebrates, most notably poultry, causing serious disease and economic loss. Like all apicomplexans, eimerians have a complex life cycle characterized by asexual divisions that amplify the parasite population in preparation for sexual reproduction. This can be divided into three events: gametocytogenesis, producing gametocytes from merozoites; gametogenesis, producing microgametes and macrogametes from gametocytes; and fertilization of macrogametes by microgametes, producing diploid zygotes with ensuing meiosis completing the sexual phase. Sexual development in Eimeria depends on the differential expression of stage-specific genes, rather than presence or absence of sex chromosomes. Thus, it involves the generation of specific structures and, implicitly, storage of proteins and regulation of protein expression in macrogametes, in preparation for fertilization. In Eimeria, the formation of a unique, resilient structure, the oocyst wall, is essential for completion of the sexual phase and parasite transmission. In this review, we piece together the molecular events that underpin sexual reproduction in Eimeria and use additional details from analogous events in Plasmodium to fill current knowledge gaps. The mechanisms governing sexual stage formation and subsequent fertilization may represent targets for counteracting parasite transmission.

This study aimed to investigate whether suboptimal incubation (SI) temperature in weeks 1 and 3 of layer embryo incubation affects their development and post-hatch adaptive capacity during infectious challenges, by using Eimeria as a model infection under normal and immediately after more challenging environmental conditions of 72 h heat exposure. Eggs (n = 160 per treatment) were incubated at optimal (OI = 37.8°C continuously) or suboptimal eggshell temperature (36.7°C, 37.8°C and 38.9°C in weeks 1, 2 and 3, respectively). At day 33 of age, half the chickens of each incubation treatment were exposed to 72 h heat (35°C), whereas the other half remained under control conditions (21°C). At day 36 of age, all chickens were inoculated with 1 ml of a phosphate buffer saline solution containing 25 000 sporulated Eimeria acervulina oocysts/ml. The adaptive response to E. acervulina was measured by BW gain and FI from days 0 to 3 post infection (p.i.), days 3 to 5 p.i. and days 5 to 7 p.i., and by oocyst production (days 4 and 7 p.i.) and lesion scores in the duodenum (day 3, 4 and 7 p.i.). Our results demonstrated that SI temperatures in weeks 1 and 3 of incubation resulted in a reduction in yolk-free BW, chick length and navel condition. Moreover, SI temperature appeared to reduce the adaptive capacity to E. acervulina. This was demonstrated by tendencies to lower FI (P = 0.07) and BW gain (P = 0.08), more duodenal lesions (P = 0.09) and higher oocyst production (P = 0.02) after inoculation of E. acervulina. Higher lesion scores and faecal oocyst numbers were especially found when suboptimal incubation was combined with heat exposure preceding the infection. In conclusion, SI layer chickens tend to be less able to cope with an infectious challenge post hatch.

Reducing the burden of Salmonella in broiler flocks presents a challenge for public health. Worldwide, grow-out broilers are routinely vaccinated to prevent or lessen clinical manifestation of other infections. In this exploratory analysis we tested if details of a routine vaccination programme delivered to conventional grow-out broilers were associated with the burden of Salmonella in the flock as it progressed through its production cycle. None of the flocks studied were vaccinated against Salmonella or received a competitive exclusion product. The flocks were reared on conventional grow-out farms in southeastern USA, and sampled in a prospective field observational study. We observed significant associations between the content and design of a grow-out vaccination programme targeting other infections and the probability of detecting Salmonella in the broiler flock at different time points throughout the production cycle. To the best of the authors' knowledge, this is the first field report of such associations.

We have extracted a protein of 14 kDa from purified oocyst walls of several Eimeria species. Polyclonal antibodies were raised in rats against the 14 kDa proteins of E. acervulina and E. tenella. On immunoblots these antisera reacted in a highly specific manner with the homologous 14 kDa antigens, but not with heterologous antigens. In addition, specific binding of the two antisera to oocyst wall fragments of E. acervulina and E. tenella was demonstrated by immunofluorescence. Partial amino-terminal sequences comprising 20 amino acid residues were obtained from the 14 kDa oocyst wall proteins of E. acervulina and E. tenella. They are characterized by an abundance of amino acids containing hydroxyl groups in their side chains (serine, tyrosine, threonine). Binding of the oocyst wall protein of E. tenella by peanut agglutinin indicates the presence of O-linked carbohydrates.

Eimeria spp. are the causative agents of coccidiosis, a major disease affecting many intensively-reared livestock, especially poultry. The chicken is host to 7 species of Eimeria that develop within intestinal epithelial cells and produce varying degrees of morbidity and mortality. Control of coccidiosis by the poultry industry is dominated by prophylactic chemotherapy but drug resistance is a serious problem. Strongly protective but species-specific immunity can be induced in chickens by infection with any of the Eimeria spp. At the Institute of Animal Health in Houghton, UK in the 1980s we showed that all 7 Eimeria spp. could be stably attenuated by serial passage in chickens of the earliest oocysts produced (i.e. the first parasites to complete their endogenous development) and this process resulted in the depletion of asexual development. Despite being highly attenuated, the precocious lines retained their immunizing capacity. Subsequent work led to the commercial introduction of the first live attenuated vaccine, Paracox®, that has now been in use for 20 years. As much work still remains to be done before the development of recombinant vaccines becomes a reality, it is likely that reliance upon live, attenuated vaccines will increase in years to come.

Codon usage has been analysed in individual gene sequences, derived from a variety of parasitic protozoa in the class Sporozoa of the phylum Apicomplexa using metric multidimensional scaling. The two groups of codon usage patterns detected reflect the two main subgroups of organisms studied (the coccidia and the piroplasms), and it is the pattern usage of synonymous codons that has the largest influence on overall codon usage in the individual genes, rather than being the pattern of amino acid composition of the gene product. The magnitude of the codon usage bias in the sequences was determined using three commonly used indices – NC', GC3s and B. In general, although relatively low levels of codon usage bias were detected in these gene sequences, codon usage bias does explain at least some of the codon usage patterns observed. Codon usage bias was observed to be dependent on the overall base composition of the genes analysed, which in turn was reflected in the types of codons that were either over-or under-represented in the nucleotide sequences. keeping with observations on prokaryotic organisms, it is speculated that the codon usage patterns detected in these parasitic protozoa are the result of directional mutation pressure on the base composition of the genomic DNA.

Immune responses of 4 inbred lines of chickens, that differ in resistance to Eimeria maxima and E. tenella, were examined. Significant differences were found in in vitro proliferation of peripheral blood lymphocytes to E. maxima sporozoite antigen, the more resistant lines C and 72 having higher responses than the more susceptible line 151. These differences existed pre-infection and were enhanced following both primary and a second infection. The proportions of lymphocyte subsets in the peripheral blood following primary infection also differed between lines, with significantly higher percentages of CD8 + and TCR1 + lymphocytes circulating in the more resistant birds. In contrast, there were few differences between lines in either resistance or in in vitro proliferation of peripheral blood lymphocytes to E. tenella sporozoite antigen either pre-infection or following a primary infection. However, after a second infection when there were significant differences in resistance between lines, as measured by oocyst excretion, there were also significant differences in lymphoproliferation with the more resistant lines 151 and 62 having higher responses than the more susceptible line C. Thus for E. maxima there is a direct relationship between resistance to infection and lymphoproliferation in response to parasite antigen. This implies that differences in cellular immunity may account for differences in resistance between lines, and since these specific responses are enhanced by infection they may also reflect important immune mechanisms. For the rather less immunogenic E. tenella, the correlation between resistance and lymphoproliferation is not so clear. However, where there were significant differences between lines, i.e. after a second infection, the direct relationship between resistance and lymphoproliferation was upheld.

The pattern of oocyst production of 8 inbred lines of chickens was compared for each of the 7 species of Eimeria which infect this host. Both the overall numbers and the pattern of oocyst production differed in the inbred lines, but there was no evidence of prolonged cycling of schizogenic developmental stages. Comparison of the numbers of oocysts produced by the different lines indicates that there may be common genetic factors affecting susceptibility to 6 of the 7 species. Surprisingly there appears to be an inverse relationship between susceptibility to E. tenella and susceptibility to the other species: lines which produced most oocysts of E. tenella produced least oocysts of the other species and vice-versa.

We have isolated and sequenced cDNA clones from Eimeria tenella and Eimeria maxima which encode proteins that share homology with a recently described family of calmodulin-domain protein kinases. The primary sequence data show that each of the protein kinases can be divided into 2 main functional domains – an amino-terminal catalytic domain typical of serine/threonine protein kinases and a carboxy-terminal domain homologous to calmodulin, which is capable of binding calcium ions at 4 ‘EF-hand’ motifs. Expression of the E. tenella calmodulin-domain protein kinase (EtCDPK) increased towards the end of oocyst sporulation, as judged by Northern and Western blotting, and indirect immunofluorescent antibody labelling showed that within a few minutes of adding sporozoites to target host cells in in vitro culture EtCDPK was found to be specifically associated with a filament-like structure that converges at the apical end of the parasite. Once the parasite entered the host cell EtCDPK appeared to be left on the host cell membrane at the point of entry, indicating a brief yet specific role for this molecule in the invasion of host cells by E. tenella.