Immunostimulatory complexes containing Eimeria tenella antigens and low toxicity plant saponins induce antibody response and provide protection from challenge in broiler chickens

Immunostimulating complexes (ISCOMs) are unique multimolecular structures formed by encapsulating antigens, lipids and triterpene saponins and are one of the most successful antigen delivery systems for microbial antigens. In the current study, both the route of administration and the antigen concentration of ISCOMs, containing Eimeria tenella antigens and saponins from native plants, were evaluated in their ability to stimulate humoral immunity and to protect chickens against a challenge infection with E. tenella. Broiler chickens were immunized with ISCOM preparations containing E. tenella antigens and the purified saponins Gg6, Ah6 and Gp7 isolated from Glycyrrhiza glabra, Aesculus hippocastanum and Gipsophila paniculata, respectively. The effects of the route of administration, dose of antigen and type of saponin used for construction of ISCOMs were evaluated for ability to stimulate serum IgG and IgM and to protect chickens against a homologous challenge. A single intranasal immunization was the most effective route for administering ISCOMs although the in ovo route was also quite effective. Dose titration experiments demonstrated efficacy after single immunization with various ISCOM doses but maximum effects were observed when ISCOMs contain 5-10mug antigen. Immunization of birds by any of the three routes with E. tenella antigens alone or antigens mixed with alum hydroxide adjuvant resulted in lower serum antibody and reduced protection to challenge relative to immunization with ISCOMs. Overall the results of this study confirm that significant immunostimulation and protection to challenge are achieved by immunization of chickens with ISCOMs containing purified saponins and native E. tenella antigens and suggest that ISCOMs may be successfully used to develop a safe and effective vaccine for prevention of avian coccidiosis.

Immunostimulating complexes incorporating Eimeria tenella antigens and plant saponins as effective delivery system for coccidia vaccine immunization

Immunostimulating complexes (ISCOMs) are unique, multimolecular structures formed by encapsulating antigens, lipids, and triterpene saponins of plant origin, and are an effective delivery system for various kinds of antigens. The uses of ISCOMs formulated with saponins from plants collected in Kazakhstan, with antigens from the poultry coccidian parasite Eimeria tenella, were evaluated for their potential use in developing a vaccine for control of avian coccidiosis. Saponins isolated from the plants Aesculus hippocastanum and Glycyrrhiza glabra were partially purified by HPLC. The saponin fractions obtained from HPLC were evaluated for toxicity in chickens and chicken embryos. The HPLC saponin fractions with the least toxicity, compared to a commercial saponin Quil A, were used to assemble ISCOMs. When chicks were immunized with ISCOMs prepared with saponins from Kazakhstan plants and E. tenella antigens, and then challenged with E. tenella oocysts, significant protection was conveyed compared to immunization with antigen alone. The results of this study indicate that ISCOMs formulated with saponins isolated from plants indigenous to Kazakhstan are an effective antigen delivery system which may be successfully used, with low toxicity, for preparation of highly immunogenic coccidia vaccine.

Acquisition of immunity toEimeria maximain newly hatched chickens reared on new or reused litter

The acquisition of immunity by chickens infected 18 h post-hatch with 100 oocysts of Eimeria maxima and reared in floor-pens in contact with their droppings was investigated. In the first experiment, birds were placed on new litter and immunity was measured at 2, 3, 4, and 5 weeks by calculation of weight gain from days 0 to 7 following challenge with 100000 oocysts or by oocyst production in the faeces from days 5 to 8 following challenge with 500 oocysts. In the second experiment, birds were placed on new litter or reused litter from the first experiment (1 week after birds from the first experiment had been removed when 6 weeks of age), and were challenged at 1, 2, and 3 weeks of age. In the first experiment, immunity had developed in birds challenged at 3, 4, and 5 weeks, judged by weight gain and oocyst production, but immunity was not complete at 2 weeks. In the second experiment, immunity had developed in birds challenged at 1, 2, and 3 weeks measured by either criterion. In both experiments, birds produced small numbers of oocysts in their faeces following challenge. Judged by the weight gain following challenge, no significant difference in the acquisition of immunity was observed whether birds were reared on new or reused litter.

Guidelines for evaluating the efficacy and safety of live anticoccidial vaccines, and obtaining approval for their use in chickens and turkeys

These guidelines are intended to aid those engaged in poultry research in the design, implementation and interpretation of laboratory, floor-pen and field studies for the assessment of the efficacy and safety of live anticoccidial vaccines for immunization of chickens and turkeys against Eimeria species. In addition to efficacy and safety requirements, manufacture, quality control and licensing considerations are discussed. The guidelines do not address subunit vaccines comprising non-viable material, but many of the principles described will be relevant to such vaccines if they are developed in the future. Guidelines are available in some countries for avian vaccines of bacterial or viral origin but specific standards for anticoccidial vaccines in poultry have not, as far as we know, been produced. Information is provided on general requirements of registration authorities (based upon regulations applicable in the European Union and the USA) for obtaining marketing authorizations for vaccines. These guidelines may assist poultry specialists in providing specific information for administrators involved in the decision-making process leading to registration of new vaccines, and are intended to facilitate the worldwide adoption of consistent, standard procedures.

Anticoccidial vaccines for broiler chickens: pathways to success

The use of live vaccines, either attenuated or non-attenuated, for the control of coccidiosis due to Eimeria infections in broiler breeder or layer chickens is well established. Use in broilers, however, has been slow to gain acceptance. This has been partly for economic reasons, but also because of perceived adverse effects on early chick growth, particularly with non-attenuated vaccines, and concerns about timely onset of protective immunity in such short-lived birds. This review describes advances in understanding of epidemiological factors and recent improvements of administration methods that have helped to allay these fears and to make the use of anticoccidial vaccines in broilers technically achievable. Topics discussed include: (1) types of commercially available vaccine, (2) vaccines in development, (3) vaccination methods and equipment, (4) basis of vaccine efficacy and immunogenic variation of parasites, (5) key factors in the survival, sporulation and dissemination of vaccinal oocysts, (6) descriptions and significance of patterns of litter oocyst accumulation and occurrence of intestinal lesions in vaccinated flocks, (7) rotation of anticoccidial vaccination and chemotherapy to restore drug sensitivity to resistant wild-type coccidia, (8) combinations of anticoccidial vaccination and chemotherapy, (9) interactions between coccidiosis and clostridiosis in broilers and compatibilities of potential control methods, (10) published performance data for live anticoccidial vaccines in broilers, (11) possible further developments of live vaccines.

Recent advances in biology and immunobiology of Eimeria species and in diagnosis and control of infection with these coccidian parasites of poultry

Avian coccidiosis, an intestinal disease caused by protozoan parasites of the genus Eimeria, occurs worldwide. It is considered to be one of the most economically important diseases of domestic poultry. For many years, prophylactic use of anticoccidial feed additives has been the primary means of controlling coccidiosis in the broiler industry and has played a major role in the growth of this industry, which now can produce about 7.6 billion chickens annually. However, development of anticoccidial resistance has threatened the economic stability of the broiler industry. Although there has been little effort by the pharmaceutical industry to develop new anticoccidials, the mounting problem of drug resistance of Eimeria species has prompted major research efforts to seek alternative means of control through increased knowledge of parasite biology, host response, and nutritional modulation. As a consequence, important advancements have been made, particularly in defining parasite antigens that have potential use in vaccines, defining the Eimeria genome, understanding the immunology of coccidial infections, and the practical applications of live vaccines. This review describes the progress in these areas, most of which has occurred within the past 10 to 15 years.

A new protocol for a challenge test to assess the efficacy of live anticoccidial vaccines for chickens

The search for vaccines to control coccidioses caused by Eimeria species in chickens (Gallus gallus) is intensifying because of the increasing threat of drug resistance to anticoccidial agents. It is important, therefore, to develop a reliable standard method for the assessment of multivalent vaccine efficacy, because many criteria generally used to judge drug efficacy are not appropriate for vaccines. The lack of correlations between oocyst production, severity of lesions and bird weight gains is discussed. Furthermore, not all Eimeria species cause pathognomonic lesions. A new protocol for a vaccine efficacy test is described which uses growth rate of chickens after virulent challenge as the primary criterion and feed conversion ratio as the secondary criterion for protection against each of the separate coccidioses caused by the seven species of Eimeria that parasitize the chicken. The benefits to this protocol over previous ad hoc experimental designs are: (1) immunization is carried out with multivalent vaccines of Eimeria species up to the maximum of seven that may infect chickens; (2) assessments of immunity are carried out for each species separately so results can not be confounded; (3) the criteria of efficacy are those that are crucial to demonstrate commercial usefulness; (4) the possibility of drawing erroneous conclusions based upon inappropriate criteria such as oocyst production or lesion scores is avoided; (5) because the same criteria are used for each species, direct comparisons may be made amongst immunities to all of the species in the vaccine being tested. Results are presented from tests of three commercial batches of Paracox attenuated anticoccidial vaccine, showing that separate virulent challenges with all seven Eimeria species were controlled in vaccinated chicks.

Use of live oocyst vaccines in the control of avian coccidiosis: experimental studies and field trials

Areas addressed in this study on the use of live oocyst vaccines to control coccidiosis include: the influence of immunocompetency of the strains and sex of the birds used; methods of delivery of vaccine; immunological variation between different strains of the same coccidial species; and the effects of combining vaccine with anticoccidial medication. The results show that vaccination with live oocysts elicited significant protection against coccidiosis, both with experimentally induced and naturally acquired coccidial infection, resulting in average bird weight gains and feed efficiency similar to that obtained with conventional anticoccidial medication.