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Immunity and Genetic Resistance to Tropical Theileriosis

a.o. biotec at goliat.ugr.es
Thu Jun 13 02:39:11 EST 1996

Immunity and Genetic Resistance to Tropical Theileriosis

	Theileria annulata is a tick-borne protozoan parasite of cattle and 
the causative agent of tropical theileriosis, or East Coast Fever. This 
disease is a serious constraint to the improvement of cattle in endemic areas 
of Africa, as European cattle imported to improve milk and meat yields are 
extremely susceptible to the disease. The disease can be controlled by a 
vaccine containing live parasite, but data about its impact on endemic areas 
was previously sketchy. A programme of research, funded by the European Union 
Science and Technology for Development (STD) programme, examined two areas 
which are essential in combatting this disease problem:
	1.- The mechanisms employed by the parasite to avoid immune detection 
leading to disease.
	2.- The first major epidemiological surgery in an endemic area 

1.- In experimentally treated animals, where the parasite was killed by drug 
treatment, it had been shown that T cells could be generated by the host to 
reject the parasite.
Continuing work from an earlier STD funded programme, this work showed that T. 
annulata is in a unique position to influence the generation of such T cell 
responses, as it infects the antigen presenting cells (APC) which are 
responsible for the induction of T cell responses.
	When T cells were stimulated by T. annulata infected APC, it was found 
that although the T cells were induced to activate and grow, that they did not 
acquire any specificity for the parasite. This was true of both CD8+ T cells, 
which directly kill infected cells and CD4+ T cells which are responsible for 
the production of soluble factors to "help" CD8+ acquire a "killer" phenotype. 
The failure to produce protective immunity during. T. annulata infection of 
susceptible animals is therefore at least partly due to alteration of normal 
immune response pathways by the parasite.

2.- The first major epidemiological survey of theileriosis was carried out in 
Morocco, giving invaluable data on disease prevalence. Approaching 100% of 
cattle in endemic areas were infected, although disease was principally 
confined to European cattle. As the majority of animals were infected, there 
was no possibility that the vaccine would induce new "carrier" cattle to the 
population. This information was used in designing and carrying out a large 
scale tissue culture vaccination programme, using a dose 100 times lower than 
attempted in other countries. The trial was extremely successful and the low 
dose significantly reduced the cost and increased the safety of the vaccine.
	The findings from both areas of the project have provided the basis 
for large advances in the control of tropical theileriosis. Vaccination in 
Morocco has now been extended to very large numbers of cattle, and vaccine 
production is currently being commercialised. The research team has 
subsequently shown that aberrant T cell responses are the critical event in 
the induction of disease, leading to sequential immune response failure.
	For further information contact the project leader, Dr. Roger C. 
Spooner, Roslin Institute, Edinbrugh EH25 9PS.

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