THE EPIDEMIOLOGY OF BOVINE TROPICAL THEILERIOSIS IN TUNISIA AND THE DEVELOPMENT OF A LIVE ATTENUATED VACCINE

biotec at goliat.ugr.es biotec at goliat.ugr.es
Sat Mar 22 06:31:12 EST 1997


THE EPIDEMIOLOGY OF BOVINE TROPICAL THEILERIOSIS IN TUNISIA AND THE 
DEVELOPMENT OF A LIVE ATTENUATED VACCINE


 	Tropical theileriosis, caused by the tickborne protozoan 
Theileria annulata is a most important disease of improved, and the 
most productive, dairy cattle in Tunisia.  The scientific work 
undertaken during the project consisted of epidemiological 
investigations on tropical theileriosis and attenuation of Tunisian 
stocks of Theileria annulata. The project (STD2A-260) was funded by 
the European Union, and was coordinated by Professor C.G.D. Brown, 
CTVM, University of Edinburgh.

	Sero-epidemiological investigations on tropical 
theileriosis showed that the infection is widespread in the 
sub-humid and semi-arid zones of Tunisia, and also present in the 
cork oak (Quercus suber) level of the humid zone.  Both endemically 
stable and endemically unstable situations were identified.  
Endemic instability, with the highest clinical disease incidence, 
was mainly observed in purebred exotic cattle, while endemic 
stability was recorded in indigenous cattle under the traditional 
management system.  Tick surveys confirmed the role of Hyalomma 
detritum as the major vector of T.annulata in Tunisia.  In 
endemically stable situations high tick infestation rates were 
observed on cattle, ensuring an early primary infection of calves 
during the first summer of life.  In endemically unstable 
situations lower infestation rates were recorded, resulting in 
varying proportions of uninfected, naive cattle up to and following 
the third theileriosis seasons.

	A preliminary evaluation confirmed the economic importance 
of tropical theileriosis.  In the sub-humid zone where a high 
incidence of clinical disease was recorded in exotic dairy cattle, 
the impact of the disease led to preliminary loss evaluation of 18 
Tunisian Dinars per female in the survey area.

	Nationwide studies on the distribution of T.annulata and 
its vector ticks were pursued in this project; these studies 
confirmed the presence of both H.detritum and T.annulata in the 
cork oak bioclimatic stage in the humid zone.

	Six stocks of T.annulata were isolated from clinical cases 
of theileriosis in the field and established  in vitro as cell 
cultures.  Five of these stocks were also isolated as infected 
ground up tick supernates (GUTS) produced from the laboratory tick 
colony of H.anatolicum excavatum and, in one case, from naturally 
infected H.detritum ticks.  These were cryopreserved in liquid 
nitrogen as definitive, representative stabilates of Tunisian 
stocks of T.annulata.

	A high degree of phenotypic and genotypic polymorphism was 
observed both between and within the T.annulata stocks. Four of 
these stocks were maintained in continuous cell culture until 
passage 200.  In vivo testing of three stocks confirmed their 
attenuation at passage 100, or at passage 200, depending on the 
stocks used.  Experiments to evaluate immunogenecity confirmed that 
a decrease in the degree of immunity to heterologous challenge was 
observed while the homologous immunity was still strong.

	Transmission to ticks followed by reversion to virulence 
was observed with one of the three attenuated stocks.

	Safety experiments performed on milking Friesian Holstein 
cows, showed that vaccination with passage 100 of the Batan 2 stock 
produced a decrease of 3% in milk production.  Vaccination with 
Batan 2 at passage 200 was better tolerated by lactating cows and 
no milk loss was detected when compared with unvaccinated control 
animals over a period of 3 weeks following vaccination.  This cell 
line, at passage 200, was selected for further trials and field 
testing as a candidate vaccine.


For further information contact:

Dr M.E.A. Darghouth
ENMV, Sidi Thabet
Tunisia

OR

Professor C.G.D. Brown
CTVM
University of Edinburgh
Easter Bush, Roslin
Midlothian EH25 9RG
Scotland
 




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