Effects of initial litter contamination level with Eimeria acervulina on population dynamics and production characteristics in broilers

Comparative study between chemical anticoccidial medication and natural prepared products on experimentally infected broiler chickens

This study was conducted in order to compare well established used chemical anticoccidial medication (diclazuril) against natural prepared safe alternative products of garlic extract (GE), Moringa oleifera (MO) leaves extract, onion extract (OE), in order to control experimentally infected with Eimeria tenella species in chickens. Performance parameter in form of average body weight (ABW) and feed conversion rate (FCR) were studied together with biochemical parameters (malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT), mortality rate, oocyst count in addition to total white blood cell (WBCs), lymphocytes and heterophils counts. Histopathological examination of intestinal tract in all test groups was studied. Results revealed that the lowest mortality rate was found in group treated with MO leaves extract. All challenged herbal extract treated groups revealed ABW and FCR lower than diclazuril treated infected group. All treated groups were lower in both average lesion score and average oocyst count two weeks post challenge when compared with control positive group indicate positive impact of all studied therapies either chemical or herbal products but with variable degrees as best effect was diclazuril followed by MO group, followed by GE group and finally group treated with OE. Experimental infection of chickens with E. tenella oocysts significantly increased MDA concentration when compared with control negative non-treated group (P < 0.01). However, infected birds fed with OE, GE, MO leaves extracts and diclazuril administration for a week pre-infection had significantly declined MDA concentrations compared with infected non-treated (P < 0.01). Control positive birds showed significant decrease in SOD and CAT activities vs. the healthy birds either at week pre-infection or at two days' post-infection (P < 0.01). However, SOD activities in birds fed with OE, MO leaves extract and diclazuril for a week pre-infection significantly higher (P < 0.01) than control positive. Histopathological finding revealed that best was group treated with diclazuril followed by group received MO, followed by group received GE and finally group received OE. It could be concluded that herbal extract may be representing a good alternative anticoccidial medications specially that the later may developed resistance for many Eimeria species in continuous use in veterinary field.

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.

Viable Eimeria oocysts in poultry house litter at the time of chick placement

The purpose of this study was to determine if Eimeria oocysts recovered from litter at the time of chick placement in commercial broiler houses contained oocysts that were infectious for chickens. Over 100 litter samples were collected from 30 poultry farms representing a total of 60 different broiler houses with 9 houses sampled more than once over 1.5 yr. The samples were collected just before the placement of newly hatched chicks and after an anticoccidial drug (ACD) or Eimeria vaccine (VAC) program, and processed for counting oocysts followed by Eimeria species determination using ITS1 PCR. Broiler chicks were inoculated with recovered Eimeria oocysts to determine if the litter oocysts were viable and capable of causing patent infection. At placement, E. maxima (Emax) oocysts were detected in 70 of 75 houses after ACD program and 46 of 47 houses after VAC program. Eimeria acervulina, E. praecox, and/or E. tenella (Eapt) were detected in 75 of 75 houses after ACD program and 47 of 47 houses after VAC program. Viability testing revealed that 33.0% of broiler houses contained viable Emax oocysts, while 46.9% contained viable Eapt oocysts. During VAC programs, the concentration of Emax oocysts at placement and the total number of Emax oocysts shed by chickens in viability studies showed a very strong correlation (r = 0.83). Likewise, during ACD programs, the concentration of Eapt oocysts at placement and the total number of Eapt oocysts shed by chickens in the viability study showed a strong correlation (r = 0.62). In general, Eimeria oocyst levels at placement and number of viable oocysts shed by chickens in the viability study were similar among houses on the same farm. However, the number of Eimeria oocysts shed in the viability studies was considerably less than expected based on the number of oocysts given. These data suggest that nearly 100% of all poultry houses contain Emax and Eapt oocysts at placement with 30 to 50% of the houses containing viable Eimeria oocysts, thus possibly representing a source of the protozoa to newly hatched chicks.

Effects of different broiler production systems on health care costs in the Netherlands

This study analyzed the effects of different broiler production systems on health care costs in the Netherlands. In addition to the conventional production system, the analysis also included 5 alternative animal welfare systems representative of the Netherlands. The study was limited to the most prevalent and economically relevant endemic diseases in the broiler farms. Health care costs consisted of losses and expenditures. The study investigated whether higher animal welfare standards increased health care costs, in both absolute and relative terms, and also examined which cost components (losses or expenditures) were affected and, if so, to what extent. The results show that health care costs represent only a small proportion of total production costs in each production system. Losses account for the major part of health care costs, which makes it difficult to detect the actual effect of diseases on total health care costs. We conclude that, although differences in health care costs exist across production systems, health care costs only make a minor contribution to the total production costs relative to other costs, such as feed costs and purchase of 1-d-old chicks.

Seasonal impact on the prevalence of coccidian infection in broiler chicks across poultry farms in the Kashmir valley

The information on the epidemiology and control of coccidian parasites of broilers in Kashmir valley is based on the reports available from other regions of the world. With this background, the present study was conducted to investigate the seasonal prevalence of the disease in the temperate agro-climatic conditions of Kashmir valley. A standard protocol for sampling was followed according to which five birds per 10,000 is sufficient to diagnose coccidiosis. Microscopic examination (under 10× and 40× objective lens) was used to reveal the presence of coccidial oocysts. Different species of genus Eimeria were identified on the basis of their predilection site, morphology and size. Coccidiosis was most prevalent in autumn 45.12 ± 2.55 (September 47.5 %, October 42.42 % and November 45.46 %) followed by summer 30.84 ± 6.86, spring 23.81 ± 2.81 and winter 20.29 ± 6.40. In summer, prevalence of disease was low but afterwards prevalence of disease rose up from August to October. In spite of high relative humidity in winter, disease showed low prevalence rate. Over all prevalence for the whole year was 29.87 %. Among species Eimeria tenella was the most dominant parasite showing highest prevalence of 18.13 %. Variation in incidence of coccidiosis with respect to seasons showed a strong correlation and data was found to be statistically significant with P < 0.05. The results obtained would be quite useful to devise appropriate and effective control strategies and prophylactic programs for coccidiosis in poultry unique to this climatic zone and other parts of the world with similar climatic and poultry production systems.

A modeller's perspective on infection dynamics within and between hosts

The goal of this case-series was to increase our understanding of some complex within and between-host infection dynamics through the creation of mathematical and computational models that are able to capture the existing host and/or parasite heterogeneity. This goal was reached through a series of research projects (regarding experimental autoimmune encephalomyelitis (EAE) in mice, Mycobacterium avium subspecies paratuberculosis infection in cattle, Eimeria acervulina infection in chicken and human malaria) that gradually build up in complexity of both the system modelled and the modelling techniques used. In this case-series, the vast majority of model components have a direct link with reality. The results have shown some detailed examples of the valuable contribution that models have in understanding infection processes. The most satisfying achievements have come from those models that were able to, in hindsight, make complicated experimental results seem obvious and logical, and where the process of building the model was as insightful as the final results. The models created in these projects help to explain a wide range of sometimes contradictory experimental results and are used to predict the effect of control measures. In addition, they generate ideas for the development of new methods of control.

Effect of Eimeria acervulina infection history on the immune response and transmission in broilers

Heterogeneity in exposure to Eimeria spp. of chickens in a flock will result in differences between individual birds in oocyst output and acquired immunity, which subsequently affects transmission of the parasite in the population. The aim of this study was to quantify effects of previous infection of broilers with Eimeria acervulina on immune responses, oocyst output and transmission. A transmission experiment was carried out with pair-wise housed broilers, that differed in infection history. This "infection history" was achieved by establishment of a primary infection by inoculation of birds with 50,000 sporulated E. acervulina oocysts at day 6 of age ("primed"); the other birds did not receive a primary infection ("naïve"). The actual transmission experiment started at day 24 of age: one bird (I) was inoculated with 50,000 sporulated oocysts and was housed together with a non-inoculated contact bird (C). Oocyst excretion and parameters describing transmission, i.e. the number of infected C birds and time passed before start of excretion of C birds, were determined from day 28 to day 50 for six pairs of four different combinations of I and C birds (I-C): naïve-naïve, naïve-primed, primed-naïve and primed-primed. Immune parameters, CD4(+), CD8(+), αβTCR(+) and γδTCR(+) T cells and macrophages in duodenum, were determined in an additional 25 non-primed, non-inoculated control birds, and in the naïve-naïve and naïve-primed groups, each group consisting of 25 pairs. Although the numbers of CD4(+) T cells and γδTCR(+) T cells increased after primary infection, none of the immunological cell types provided an indication of differences in infectivity, susceptibility or transmission between birds. Oocyst output was significantly reduced in primed I and C birds. Transmission was reduced most in the primed-primed group, but nonetheless transmission occurred in all groups. This study also showed that acquired immunity significantly reduced oocyst output after inoculation and contact-infection, but not sufficiently to prevent transmission to contact-exposed birds.

The origins of apicomplexan sequence innovation

The Apicomplexa are a group of phylogenetically related parasitic protists that include Plasmodium, Cryptosporidium, and Toxoplasma. Together they are a major global burden on human health and economics. To meet this challenge, several international consortia have generated vast amounts of sequence data for many of these parasites. Here, we exploit these data to perform a systematic analysis of protein family and domain incidence across the phylum. A total of 87,736 protein sequences were collected from 15 apicomplexan species. These were compared with three protein databases, including the partial genome database, PartiGeneDB, which increases the breadth of taxonomic coverage. From these searches we constructed taxonomic profiles that reveal the extent of apicomplexan sequence diversity. Sequences without a significant match outside the phylum were denoted as apicomplexan specialized. These were collated into 9134 discrete protein families and placed in the context of the apicomplexan phylogeny, identifying the putative origin of each family. Most apicomplexan families were associated with an individual genus or species. Interestingly, many genera-specific innovations were associated with specialized host cell invasion and/or parasite survival processes. Contrastingly, those families reflecting more ancestral relationships were enriched in generalized housekeeping functions such as translation and transcription, which have diverged within the apicomplexan lineage. Protein domain searches revealed 192 domains not previously reported in apicomplexans together with a number of novel domain combinations. We highlight domains that may be important to parasite survival.

A survey of the economic impact of subclinical Eimeria infections in broiler chickens in Norway

The objective of this work was to examine the impact of subclinical coccidial infection on commercial performance, expressed as a modified European Production Index, in broilers. Performance data, and litter and faecal samples, were collected from two independent observational surveys of Norwegian broilers receiving in-feed narasin during 2000 to 2004. Numbers of oocysts per gram (OPG) of litter collected during rearing (Study 1) or faecal samples collected at slaughter (both studies), and relative frequencies of Eimeria species categories (both studies) were calculated. Polymerase chain reaction-based identification of Eimeria species was performed in Study 2. A definition of flocks at risk of impaired performance associated with coccidia ("risk flock"), using the predominant species and OPG level as criteria, was tested. Coccidia had a significant effect on performance in the first, but not the second study. In Study 1 the following coccidia variables were found to be associated with impaired performance in multivariate models: OPG at slaughter (ordinal), mean OPG during rearing (ordinal) and "risk flock" (binomial). The European Production Index was approximately 9% lower in flocks with infection levels >50 000 OPG at slaughter in Study 1. The composition of coccidial populations shifted between Study 1 and Study 2, from a dominance of medium and large oocysts to a dominance of small oocysts. There was a substantial increase in prevalence of coccidial infection from Study 1 to Study 2, but mean infection levels were similar in the two surveys. The "risk flock" definition was useful as an indicator of coccidia-associated performance loss in Study 1, where subclinical coccidiosis was an important factor. The results suggest that the economic importance of subclinical coccidiosis may vary substantially with time, and they emphasize the need for population studies on the importance and dynamics of specific coccidial infections under different field conditions.

Effects of heterogeneity in infection-exposure history and immunity on the dynamics of a protozoan parasite

Infection systems where traits of the host, such as acquired immunity, interact with the infection process can show complex dynamic behaviour with counter-intuitive results. In this study, we consider the traits ‘immune status’ and ‘exposure history’, and our aim is to assess the influence of acquired individual heterogeneity in these traits. We have built an individual-based model of Eimeria acervulina infections, a protozoan parasite with an environmental stage that causes coccidiosis in chickens. With the model, we simulate outbreaks of the disease under varying initial contaminations. Heterogeneity in the traits arises stochastically through differences in the dose and frequency of parasites that individuals pick up from the environment. We find that the relationship between the initial contamination and the severity of an outbreak has a non-monotonous ‘wave-like’ pattern. This pattern can be explained by an increased heterogeneity in the host population caused by the infection process at the most severe outbreaks. We conclude that when dealing with these types of infection systems, models that are used to develop or evaluate control measures cannot neglect acquired heterogeneity in the host population traits that interact with the infection process.

A model for the dynamics of a protozoan parasite within and between successive host populations

Parasite-host systems often include an obligatory environmental stage in the parasite life-cycle, which can be transmitted between successive populations. Complexity even increases if immunity only gradually develops upon re-infection. For a better understanding of such systems we study Eimeria spp. in chickens, a protozoan parasite transmitted through oocysts on the floor. This paper deals with dynamics within and between successive cohorts of chickens by coupling a within-host description of the parasite life-cycle (with immunity) to re-uptake of oocysts from the environment. First the initial environmental oocyst level is related to the maximum infection load within a cohort, as a measure of production damage, from which we conclude that minimum damage levels can be observed with intermediate oocyst levels. Then we relate the initial to the final oocyst level of a cohort, and study the dynamics between cohorts in relation to an oocyst cleaning efficiency after each cohort. The resulting unstable dynamics lead to the conclusion that it will often be impossible to minimize damage by repeatedly cleaning with the same effort: it may be necessary to artificially increase oocyst levels in the shed before each chicken cohort.

Vaccination as a control strategy against the coccidial parasitesEimeria,ToxoplasmaandNeospora

The protozoan parasitesEimeriaspp.Toxoplasma gondiiandNeospora caninumare significant causes of disease in livestock worldwide andT. gondiiis also an important human pathogen. Drugs have been used with varying success to help control aspects of these diseases and commercial vaccines are available for all three groups of parasites. However, there are issues with increasing development of resistance to many of the anti-coccidial drugs used to help control avian eimeriosis and public concerns about the use of drugs in food animals. In addition there are no drugs available that can act against the tissue cyst stage of eitherT. gondiiorN. caninumand thus cure animals or people of infection. All three groups of parasites multiply within the cells of their host species and therefore cell mediated immune mechanisms are thought to be an important component of host protective immunity. Successful vaccination strategies for bothEimeriaandToxoplasmahave relied on using a live vaccination approach using attenuated parasites which allows correct processing and presentation of antigen to the host immune system to stimulate appropriate cell mediated immune responses. However, live vaccines can have problems with safety, short shelf-life and large-scale production; therefore there is continued interest in devising new vaccines using defined recombinant antigens. The major challenges in devising novel vaccines are to select relevant antigens and then present them to the immune system in an appropriate manner to enable the induction of protective immune responses. With all three groups of parasites, vaccine preparations comprising antigens from the different life cycle stages may also be advantageous. In the case ofEimeriaparasites there are also problems with strain-specific immunity therefore a cocktail of antigens from different parasite strains may be required. Improving our knowledge of the different parasite transmission routes, host-parasite relationships, disease pathogenesis and determining the various roles of the host immune response being at times host-protective, parasite protective and in causing immunopathology will help to tailor a vaccination strategy against a particular disease target. This paper discusses current vaccination strategies to help combat infections withEimeria,ToxoplasmaandNeosporaand recent research looking towards developing new vaccine targets and approaches.

Intestinal Mucosal Mast Cell Immune Response and Pathogenesis of Two Eimeria acervulina Isolates in Broiler Chickens

Four experiments were conducted comparing intestinal immune responses to 2 isolates of Eimeria acervulina (EA), EA1 and EA2. In experiments 1 and 2, broiler chicks of 2 commercial breeds were divided into control (nonchallenged), EA1-, or EA2-challenged groups. On d 6 postchallenge (PC), changes in BW were determined, intestinal lesions were scored, and duodenal tissue was evaluated for morphometric alterations and mucosal mast cell numbers. EA1 produced classical duodenal lesions and reduced villus height to crypt depth ratios compared with controls; however, no differences were found in mast cell counts. EA2 produced different results, and observed data were suggestive of an anaphylactic-like intestinal secretory response compared with EA1 or controls. In experiment 3, tissues were analyzed from d 2 through 6 PC. Villus atrophy and crypt hyperplasia were increased on d 5 PC in both challenged groups. Mast cell counts were significantly greater on d 3 and 4 PC in EA1-challenged birds. In experiment 4, EA2 oocysts were cleaned with 5.25% sodium hypochlorite to evaluate the possibility of a bacterial contaminant contributing to the pathogenesis of intestinal alterations. No evidence of a bacterial contaminant contributing to the pathology was observed. These data are indicative of differential host response and immunovariability between different isolates of the same Eimeria species in 2 breeds of commercial broiler chickens.

Eimeria acervulina: influence of corticosterone-induced immunosuppression on oocyst shedding and production characteristics in broilers, and correlation with a computer simulation model

An experiment was conducted to investigate the effects of immune responsiveness on excretion of oocysts after E. acervulina infection and subsequent effects on production characteristics of broilers (Gallus domesticus). These effects were determined in broilers repeatedly infected with 2.85 x 10(3) oocysts of E. acervulina and treated with various dosages of corticosterone in the diet (0, 10, 20 and 30 p.p.m.). Corticosterone treatment did not have an effect on the peak oocyst excretion, although it was administered from 4 days before initial infection. The number of oocysts excreted shortly after the peak and the length of the excretion period were increased in corticosterone-treated groups. The absence of a difference in peak oocyst excretion was ascribed to the existence of a time-lag between first contact with the parasite and rate of development of protective immunity. In a recently developed computer simulation model this period was assumed to be 5 days. Assuming that immunosuppression, through corticosterone, is only effective when protective immunity is in operation, the results indicate a time-lag of at least a few days, which supports the inclusion of such a time-lag in the computer simulation model. General immunosuppressive effects of the corticosterone treatment, monitored by antibodies and mitogen-induced lymphocyte stimulation confirmed that immunosuppression occurred shortly after medication started. Infection did not have a significant influence on production characteristics in animals without dietary corticosterone. However, with increasing corticosterone levels the negative effects of infection on production also increased.