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Mechanisms of pathogenesis and immunity in tropical theileriosis: their relevance to vaccine development and disease control


- Study the epidemiology of bovine Tropical Theileriosis in the Mediterranean Basin;
- Expand the cell line vaccination programme for Morocco and study the effects of vaccination on epidemiology;
- Study the pathogenesis of disease to answer several fundamental problems that have been identified in our attempts to produce immunity with dead parasite material;
- To expand the collaboration with Morocco and Turkey built up under STD1 and 2 and extend this to Germany;
- Organise a co-ordination meeting of workers from Theileriosis endemic areas and Europe in Turkey in 1994 and a tick and tick borne diseases meeting in China in 1996.
- In Morocco a detailed epidemiological survey over 4 years was carried out in one of the major dairying regions before and after vaccination. This was supplemented by a national survey in all the main dairy production areas in 1995. In the Sidi Bennour region Theileriosis was and is the major cause of loss in imported black and white cattle. Disease is prevented by vaccination and the tick infection rates are not significantly affected by vaccination. The disease is present at a significant level (over 50%) in all of the main dairy areas. It is the main cause of death in dairy cattle. Economic importance is estimated at approximately $15 million per annum. The only vector is Hyalomma detritum.
- An ELISA test was developed in Morocco for the diagnosis of Tropical Theileriosis and two new enzymes based tests for anti theilerial antibodies were developed in Roslin and Borstel Germany. The Roslin test, using peroxidase, has been used for the nation-wide epidemiological studies in Morocco. It has significant advantages over the indirect fluorescent antibody test, particularly because of the permanence of the preparations, ease of reading and the fact that a fluorescent microscope is not required. It has now replaced IFAT in Morocco.
- In Turkey the epidemiology of Theileriosis was studied in three areas, Eastern Anatolia, the Marmara region and the Mediterranean Coast. The ticks transmitting the disease were found to be Hyalomma anatolicum anatolicum and Hyalomma detritum in most regions although in the Mediterranean region H. anatolicum excavatum transmitted the disease. The seasonal activity of larval, nymph and adult stages was identified. The incidence of the disease was 67% in Eastern Anatolia, 22% in the Mediterranean coast and 2% in the Marmara region.

- In Morocco a low dose fresh cell line vaccine has been successfully tested in extensive field trials. It was shown that it was equally effective one week after preparation when stored at ambient temperature thus showing that producing frozen vaccine is unnecessary. It used 104 infected cells compared with the existing concentrations of 106 or more used in other countries. It thus significantly reduced the cost of vaccine production. Vaccination reduced the incidence of the disease by 98% in endemic areas. It did not change tick infection rates significantly on the farms where it was used. It is currently undergoing commercialisation.
- Some studies on the high cell dose frozen vaccine in Turkey were carried out. It also produced high levels of sero conversion and was effective in the areas where it was used.

Pathogenesis and immunity
- A very collaborative research programme involving the Roslin Institute, Centre for Tropical Veterinary Medicine, and Institute of Cell, Animal and Population Biology in Edinburgh and the Forschungszentrum in Borstel Germany we have :
- shown that parasite evades the immune response in lethal infections through the stimulation of high levels of IFN-gamma and disabling of cytotoxic T cells which lose CD2;
- provided evidence for a major role for macrophages in the pathology of the disease, as hosts for schizonts and in granulomatous reactions, and in protective immune mechanisms, via nitric oxide synthesis;
- shown that following lethal sporozoite infection, germinal centres in lymph nodes were totally destroyed whereas following cell line immunisation there was a normal immune response with germinal centres;
- identified peptides on the surface of macroschizont infected cells that are recognised by cytotoxic T cells from immune animals. These antigens are potential candidates for a molecular vaccine;
- shown using lymphatic cannulation that parasite transfer was essential for immunity. We also showed that reimmunisation with the same cell line did not boost immunity because the vaccine was rejected like a graft;
- identified novel antigens and cytokine profiles that may correlate with the ability of cell lines to produce disease. This may enable us to attenuate cell lines without prolonged culture;
- shown that Sahiwal (Bos indicus) was more resistant to T. annulata infection than calves of West European breeds (Bos taurus).


- Third EU co-ordination meeting on Tropical Theileriosis, Antalya, Turkey. October 1994.
A highly successful co-ordination meeting was held in Antalya Turkey in October 1994. This brought together over 60 workers from all of the major areas where Theileriosis was endemic. The proceedings have been published and provide a valuable source of information on the status of research and control of the disease at that time. Copies of the proceedings are available from the co-ordinator;

- EU International Symposium on Ticks and Tick Borne Diseases, Xi'an China September 1996.
A second co-ordination meeting was organised in Xi'an China. This brought together workers on tick borne diseases from all regions of China with representatives from Europe, Australia, Thailand, Japan, India, Turkey, Tunisia, Morocco and South Africa. It presented an opportunity for those within China to learn of the latest developments in research and control outside China and from those from outside to learn of the research underway in China and of the main disease problems in the country. Tropical Theileriosis is well controlled with a novel cell line vaccine. Theileria Sergenti for which there is no vaccine is a major problem particularly in imported European breeds and in sheep Theileria hirci causes high mortality. Babesiosis is also important as is anaplasmosis. The proceedings of this meeting will be published in early 1997 and will also be available for the co-ordinator.

Follow up

- In IC18-CT95-0004 the basic immunology of Theileriosis and generation of immunity by vaccination is being followed up. Also epidemiology post vaccination and the development of better diagnostic tests are continuing and they are being used for epidemiological studies in Turkey and Tunisia;
- It is hoped that the meeting in Xi'an will lead to much expanded collaboration with China.
- Tropical Theileriosis is arguably the major constraint to cattle production from Morocco to China. TS3*CT92-0143 addressed important aspects of epidemiology, pathogenesis, immunity and control;
- Built on the work already started in Morocco under STD2 on the epidemiology and economic importance of the disease and extended this to Turkey. It also involved collaboration with TS3*CT91-0019 which studied the epidemiology of Theileriosis in Tunisia;
- Continued the development and commercialisation of a novel formulation of a cell line vaccine;
- Collaboration between the Roslin Institute, Centre for Tropical Veterinary Medicine (C.T.V.M) and Institute of Cell Animal and Population Biology, Edinburgh, together with the Institute of Experimental Biology and Medicine, Borstel, Germany concentrating on the pathogenesis of the disease.
This had three main components :
- A study of the immune response to Theileria annulata in vivo using particularly lymphatic cannulation;
- An investigation into the pathology of the disease using histopathology and immunohistochemistry and the role of cytokines in the pathogenesis of disease;
- Study of the response of pure-bred Bos indicus to infection.
- Support to the Centre for Tropical Veterinary Medicine to provide parasite and animal facilities for this and other EU theileriosis projects;
- A co-ordination meeting of all workers in the field of theileriosis was organised in Turkey in 1994;
- An International Symposium on Ticks and Tick borne diseases was held in China in 1996.


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