VACCINES AGAINST ANIMAL COCCIDIOSES

Objective

GENERAL DESCRIPTION OF THE ACTION

1. BACKGROUND

Coccidioses are infectious diseases of animals or humans caused by parasitic protozoa of the subclass "Coccidia". This group includes several genera of major importance such as Eimeria, Isospora, Cryptosporidium, Sarcocystis, Toxoplasma and Neospora. These parasites are widely distributed throughout the world and are known to cause various forms of disease in a broad spectrum of animal species, but particularly in poultry, cattle, sheep, goats, pigs and rabbits. Some of these protozoa (Cryptosporidium, Sarcocystis, Toxoplasma) are transmissible from vertebrate animals to man, causing significant zoonotic infections. Cryptosporidium and Toxoplasma are of special current interest as they are life-threatening opportunistic parasites in patients with AIDS.

1.1. Coccidioses in poultry

Several species of the genus Eimeria cause damage to the intestine of poultry and induce retardation of growth, depression of egg laying capacity, severe disease, death and in consequence high economic losses. Without intensive control measures, economic poultry production would be unpractical.

At present, effective control of coccidioses is based on hygienic measures and chemoprophylaxis using antiparasitic drugs (= anticoccidia). The annual worldwide sales of anticoccidia are estimated to amount to US $250 million. This figure indicates the economic importance of poultry coccidioses.

1.2. Coccidioses of other animals

Similar forms of diseases are caused by several Eimeria species in ruminants and rabbits and by Isospora suis in pigs. Cryptosporidium parvum has been identified as a major cause of diarrhoea in calves and other animals, and Toxoplasma gondii is responsible for abortion in sheep and other animal species. Sarcocystis species are frequently found as muscle parasites in slaughter animals. Neospora caninum is a parasite which was detected only in 1988 and which is apparently closely related to Toxoplasma gondii. The biology of this parasite is still unexplored but it is known that N. caninum may cause general infections with paralysis in dogs and cats and abortions in various species of animals (cattle, sheep).

1.3. Coccidia as causative agents of zoonoses

Some of the parasites mentioned above may be transmitted from vertebrate animals to man. For example, in Switzerland and other countries about 40-50% of the young adults are infected with Toxoplasma gondii, and this rate may increase to nearly 80% in the age group over 65 years.

Recent epidemiological studies in France have indicated that humans acquire the infection mainly by consumption of raw or undercooked meat of slaughter animals. In most cases the Toxoplasma infection in humans is asymptomatic, but abortion and malformations of the foetus may occur after primary infection of pregnant women, and cerebral or generalized symptomatic infection is quite frequent in patients with AIDS. Cryptosporidium parvum is one of the major opportunistic parasites causing diarrhoea in patients with AIDS, and Sarcocystis is also responsible for intestinal disease in humans. It is unknown whether or not N. caninum is infectious for humans.

1.4. Conventional control of coccidioses

As mentioned above, coccidioses in poultry and partially also in rabbits, ruminants and pigs are at present controlled by hygienic measures and chemoprophylaxis. Chemoprophylaxis is effective but may lead to drug residues in meat and drug-resistance of the parasites which is an acutely increasing problem. Such control measures do not exist for cryptosporidiosis, sarcocystiosis or toxoplasmosis. Therefore, there is an urgent need for innovative approaches to improved control of coccidioses.

1.5. Innovative approaches to control of coccidioses

An innovative approach to control of coccidioses is the development of vaccines stimulating immune protection in the host animals and protecting them from detrimental influences of the infection. By immunization, the transmission cycles of the parasites may be interrupted or inhibited and diseases prevented.

There is ample evidence that all of the parasite genera mentioned above are able to induce immunity after natural or experimental infection. Therefore, prospects for vaccine development are favourable.

2. Current state of research

The current state of research and concepts for strategies of vaccine development against parasitic infections have been summarized by Smith (1992) in the framework of COST Action 89. Special aspects of vaccination against coccidioses were recently reviewed by Danforth et al. (1993), Long (1993), Shirley (1993), Tomley et al. (1993) and Wallach (1993).

In the field of poultry coccidioses - which is used here as an example - the following strategies for inducing immunity in chickens have been worked out by European groups which were involved in COST Action 89.

2.1. Live vaccines

A group in the United Kingdom (M. Shirley and co-workers) was actively involved in the development of a live vaccine against Eimeria species in chickens. This vaccine is now produced by Pitman-Moore as Paracox (r). It includes genetically stable precocious lines of all 7 pathogenic species of Eimeria in chickens. It is expected that this vaccine will mainly be used in breeders and replacement hens. This vaccine represents a new principle based on the selection of genetically stable parasite lines with abbreviated development in the host, low pathogenicity and good immunogenic properties. Another vaccine of this type was registered in the Czech Republic as Livacox (r) (COST 89, 1993).

According to information from French and Belgian groups (P. Coudert, R. Hamers et al.) all 10 relevant Eimeria species in rabbits are highly immunogenic and are likely candidates for selection of precocious lines. Co-operative research between various groups has been initiated to evaluate further the prospects for vaccine development on the same basis against rabbit coccidia (COST 89, 1993).

In the field of toxoplasmosis, a live vaccine has been produced and is now on the market (Toxovax (r)). This vaccine is used for immunization of sheep and to protect them against abortion caused by toxoplasmosis.

2.2. Recombinant vaccines

Various antigens or clones have been characterized, including for example a 230 kDa protein exclusively expressed by gametocytes of Eimeria maxima (M. Wallach, Switzerland), a recombinant clone recognized by a monoclonal antibody against Eimeria bovis (C. Homrighausen, Germany), cDNA clones encoding for microneme proteins of Sarcocystis muris (H. Klein, S. Lechner, Germany) or cDNA clones encoding for antigens of E. acervulina which are protective in chickens (P. Pery, France). Further studies are being carried out on the characterization and production of several recombinant antigens and the evaluation of their immunogenic properties for vaccine (COST 89, 1993).

2.3. Maternal transfer of immunity

Groups in Switzerland (M. Wallach, N. Smith et al.) have shown that vaccination of laying-hens induced antibody transfer via egg yolk and that these antibodies protected chickens against infection with Eimeria maxima. Several recombinant antigens were less effective in immunostimulation than "natural" antigens.

Maternal transfer of immunity may be of high practical importance in vaccination programmes, as the vaccine could easily be applied to the laying-hens, and chickens would have a basic protection immediately after hatching from the eggs (COST 89, 1993). Vaccination of laying-hens should also be possible with recombinant antigens. Studies in this direction are being carried out within the COST 89 group.

2.4. Summary

The abovementioned data show that several innovative strategies of vaccine development have been worked out within COST Action 89, but further and new studies are necessary to develop vaccines based on recombinant antigens. Live antigens may be used for some time, but vaccines containing no live antigen would represent a much better solution to the problem.

3. International Co-operation within COST and with other International Scientific Programmes

Supported by COST Action 89 and the Bridge Programme, several groups of scientists in universities and some laboratories of industries have developed scientific co-operation and technical exchange. In this context, laboratory visits supported by the Bridge Programme were particularly useful. For example, groups in France, Belgium, Germany, the Czech Republic and Switzerland co-operated in various fields.

In this Action, co-operation has to be continued and extended as vaccine development against diseases caused by many different parasite species (for example in chickens, 7 Eimeria species!) is a very complex task which can be solved only by shared research responsibilities and international co-operation.

The Action will be focused on co-operative projects, and groups from participating countries will be asked to submit short descriptions of co-operative projects to the Management Committee as a basis for research co-ordination. In this way, the relatively small research basis of single groups can be expanded. International scientific exchange within a COST Action is also advantageous with regard to co-operation with international industrial companies and to research support in east European countries. During an International Congress on Coccidioses in Canada in June 1993, the co-operation of European research groups within COST Action 89 was regarded as valuable by research groups from other regions. Some of them (for example, from Australia and the USA) expressed interest in co-operating with the European groups within a COST Action.

The Action will be linked to national and international research programmes implemented by the various groups of the participating countries.

4. Objectives of the Action

The main objectives of the Action will be the following:

- evaluation of new vaccination strategies;

- development of new vaccines, preferably on the basis of recombinant antigens;

- study of innovative ways for vaccine application;

- preparation of recommendations for industrial production and efficacy and safety evaluation of vaccines;

- development of biomathematical models for evaluating the potential impact of immunization on epidemiology of infections with coccidia.

In this context, the following research projects should be given high priorities:

(a) Basic studies on all aspects of molecular biology and immunology with potential relevance for vaccine development.

(b) Comparative study of the efficacy of the following immunization strategies:

- immunization of chickens by maternal transfer of protective antibodies via the eggs;

- immunization of chickens in their first weeks of life by oral application of live or recombinant vaccines.

Recent results indicate that both immunization strategies are effective in certain situations and both have advantages and disadvantages. A combined application of the two strategies might be a valid solution, but this has to be carefully studied in long-term experiments over several years including all the important Eimeria species of chickens.

(c) Study of the role of maternal transfer of immunity in coccidioses of rabbits and other mammals.

(d) Production of recombinant antigens and evaluation of their immunogenic properties.

(e) Study of eukaryotic expression systems to produce modified parasite proteins.

(f) Evaluation of various adjuvants for vaccine application (bacterial products, Arlacel etc.)

It has been shown that duration of immunity against Eimeria maxima in chickens can be considerably prolonged if Arlacel is applied to laying-hens prior to homologous infection. These results indicate that the potential of adjuvants should be further studied.

(g) Evaluation of viral and bacterial vectors for antigen presentation.

In parasitic infections, good immunity often develops only slowly. Extended presentation of protective antigens may therefore improve immune stimulation. Hence, expression of parasite antigens in avirulent recombinant viral or bacterial vectors appears an attractive way for prolonged antigen presentation.

Such studies could include Salmonella typhimurium variants (gal E mutant and other variants) and vaccinia virus (Smith, 1992). The studies should be focused on vector systems which are already used for routine vaccination.

(h) In vaccination programmes, biomathematical and epidemiological considerations are often neglected.

In this Action, these aspects should be studied in an early phase of vaccine development. For example, biomathematical models are required to define the degree of immune protection which has to be achieved in an animal population in order to reduce disease transmission to the required low level and to prevent outbreaks of the disease.

(i) These studies will be mainly carried out with Eimeria and Isospora species of domestic animals. However, similar studies with other coccidia (Cryptosporidium, Sarcocystis, Toxoplasma and Neospora) are also of high interest with regard to vaccine development.

A co-ordinated co-operative action may provide industries with the necessary basic knowledge for vaccine production. This may have impact on industrial competitiveness. In this context, questions of patent regulation and secrecy agreements have to be considered.

5. Scientific content

The scientific value of the Action can be summarized as follows:

- the implementation of vaccination programmes - based primarily on recombinant vaccines - against one or more of the coccidial infections of domestic animal or further progress in this direction would represent an important step towards a new area in the control of parasitic infections in animals and in preventing or reducing economic losses caused by parasitic diseases;

- such vaccination programmes against parasitic diseases of animals are also of high scientific interest for human medicine. Hence, results from the Action may also be supportive for medical parasitology, and vaccination against zoonotic parasites in animals (for example, toxoplasma and Cryptosporidium) may lead to the prevention of these infections in humans;

- drug application to animals for therapeutic or chemoprophylactic purposes may lead to drug residues in animal-derived food products used for human consumption. Such residues, and also the development of drug-resistant parasite strains, could be avoided by vaccination programmes;

- industrial production of vaccines can be facilitated by contributions of basic knowledge in this field;

- the development of biomathematical models for prospective studies on the influence of immunization on epidemiology of coccidioses is a novel approach which could have an impact on other fields of parasitology.

6. Timetable

The Action is scheduled for five years. In this period the following activities are planned:

1994-1996 (3 years): (a) Basic studies on molecular and immunological aspects of coccidioses.

(b) Basic studies on vaccine development, adjuvants and live vectors.

(c) Biomathematical modelling.

1997-1998 (2 years): (a) Basic studies on molecular and immunological aspects of coccidioses.

(b) Large-scale field trials with biomathematical evaluation.

7. Organization and Management

7.1. Management Committee

The Action will be co-ordinated by a Management Committee (MC).

7.2. Working Groups

The establishment of the following working groups will be suggested:

- Working Group 1: Poultry coccidiosis
- Working Group 2: Mammalian coccidiosis
- Working Group 3: Cryptosporidiosis
- Working Group 4: Sarcoystiosis, Toxoplasmosis and Neosporosis
- Working Group 5: Biomathematics
- Working Group 6: Immunology, adjuvants and live vectors
- Working Group 7: Molecular biology and biotechnology.

7.3. Admission to, and follow-up of, the Action

Scientists should be admitted for participation in the Action under the following preconditions:

- submission of short description of ongoing and planned projects and co-operation within the Action. The MC shall select for co-operation only those groups which are directly involved in the major fields of research indicated above;

- written consent to submit short annual research reports to the MC, to mention the COST co-operation in their publications and to submit lists of publications in context with the Action.

Progress of the Action will be supervised by the chairmen of the Working Groups and members of the MC. Results will be published in scientific journals and in annual reports of the Action.

8. Economic dimension of the action

8.1. Funding of research

Scientists and institutes participating in the Action have to obtain funding of their research programmes from funding organizations of their own countries. The success of the Action will depend largely on the willingness of the signatory countries to make every effort to ensure that the necessary funds will be made available. Funds should be provided for periods of at least 2 to 3 years in order to guarantee continuity of research.

It is estimated that the Action will involve 60 to 90 scientists. Assuming that about 50% of their capacity would be devoted to work related to the Action, the annual number of man-years would be 30 to 45 and the total number in 5 years 150 to 225.

Based on these figures, the salaries for scientists are estimated as follows:

- for 1 year : 30 to 45 x ECU 60 000 = ECU 1,8 - 2,7 million
- for 5 years: = ECU 9,0 - 13,5 million.

According to a general estimation, an annual budget of about ECU 15 000 per scientist would be required for communicables resulting in totals of:

- for 1 year : 60 to 90 x ECU 15 000 = ECU 0,9 - 1,35 million
- for 5 years: = ECU 4,5 - 6,75 million

8.2. Administrative costs of the MC

The co-ordination of the Action by the Chairman of the MC creates extra costs for administrative personnel, materials and for phone calls, fax etc. These costs are estimated to be ECU 15 000 per year including a salary for a part-time secretary.

The signatory countries should ensure that this financial support is provided to those scientists and institutions who are willing to function as chairman of the MC and secretariat of the MC, respectively.

Current status
The status of the COST 820 Action, as at 1st December 1996, is that the following European countries are listed as participants : Austria*, Belgium, Czech Republic, Denmark, France, Germany, Hungary, Italy, Ireland, Netherlands, Poland, Spain, Sweden, Switzerland and United Kingdom.
Note that Austria has observer status in the Management Committee.
Working Group organisation
Six Working Groups have been established as part of the COST 820 Action :
WG1 Avian coccidiosis (Co-ordinators : M. W. Shirley and M. H. Roos)
WG2 Mammalian coccidiosis (Co-ordinators : H-J. Burger and J. Catchpole)
WG3 Cryptosporidiosis and cyclosporosis (Co-ordinators : D. De Graaf & V. McDonald)
WG4 Sarcocystiosis, toxoplasmosis and neosporosis (Co-ordinators : M. Rommel & D. Buxton)
WG5 Biomathematical modelling Co-ordinators : M. Vertommen & A. Cornelissen)
WG6 Immunology and cell biology (Co-ordinators : P. Pery & F. Tomley)
Short-term scientific missions
More than 15 scientists have made visits to laboratories of other members of the COST820 Action and this activity is regarded as a major component More than 15 scientists have made visits to laboratories of other members of the COST820 Action and this activity is regarded as a major component to the success of the Action.
Work planned
Completion of a database of reagents and parasites, relevant to work on coccidial parasites, that are held in laboratories associated with COST 820.

Programme(s)

IC-COST - European cooperation in the field of scientific and technical research (COST), 1971-

Topic(s)

4 - Agriculture and Biotechnology

Call for proposal

Data not available

Funding Scheme

Data not available

Coordinator

CEC

EU contribution

No data

Address

Rue de la Loi 200
1049 Brussels
Belgium

Total cost