Genetic Analysis: Biomolecular Engineering
Vaccination against ticks (Boophilus spp.): the experience with the Bm86-based vaccine Gavac™☆
Introduction
A major veterinary problem for cattle in tropical and subtropical regions is tick infestation and, particularly, infestation by Boophilus spp. Tick infestation produces weakness of the animals affecting milk production and transmits diseases like babesiosis and anaplasmosis. Conventional control methods include the use of chemical acaracides with partially successful results, but this treatment has certain implicit drawbacks such as the presence of residues in the milk and meat and the selection of chemical-resistant tick strains [1], [2], [3].
Alternative approaches for tick control, such as the use of natural host resistance and development of vaccines to induce an immunological response against tick infestations, have been conducted [4], [5].
The protective ‘concealed’ antigen Bm86 was identified from the gut of semi-engorged adult female ticks [1], [6] and was obtained by recombinant DNA technology [5], [7]. Two vaccines containing the recombinant Bm86 antigen have been registered and released to the market: one in Cuba in 1993 and in other Latin American countries during 1994–1997 [8] (Gavac, Heber Biotec S.A., Havana, Cuba) and the other in Australia in 1994 [9] (TickGARD, Hoechst Animal Health, Australia). Field trials performed in Cuba [10], Brazil [11], Argentina [12], Colombia [12] and Mexico [12] were successful in the control of tick populations by means of the recombinant vaccine Gavac against B. microplus. The Australian group was also successful in showing the efficacy of the vaccine in Australia [9]. These vaccines mainly reduce the average fertility of adult ticks instead of causing high mortality [5], [7].
Babesiosis is transmitted by ticks in cattle and is mainly produced by species of protozoan parasites of the genus Babesia named Babesia bovis and B. bigemina [13]. These hemoparasites destroy bovine erythrocytes by haemolysis. Although substantial effort has been placed towards the development of vaccines against Babesia species [14], [15], the main control method to prevent babesiosis in Africa and South America involves the use of chemical acaricides to control tick populations. In Australia, an attenuated live vaccine has been used successfully to control babesiosis [14], [15].
This paper reviews the results obtained with the application of Gavac for the control of Boophilus spp. infestations in various countries of the world. The results clearly demonstrate the advantage of the vaccination and support the application of Gavac for the control of cattle tick infestations.
Section snippets
Experimental designs
Three types of experiments are considered in the manuscript: (a) controlled pen trials; (b) controlled field trials; and (c) field trials under production conditions.
(a) In controlled pen trials, cattle were randomly assigned to vaccinated and control groups and artificially challenged with tick larvae employing cotton chambers or ear bags to assure tick collection (Table 1). Adult female ticks daily collected from vaccinated and control cattle were counted, weighted and assessed for egg laying
Results and discussion
The recent development of vaccine formulations against cattle tick infestations has become an alternative way for the control of this ectoparasite which causes important economic losses in tropical cattle production.
The vaccine formulation Gavac contains a P. pastoris-derived antigen obtained after purification in a particulated and glycosylated form [17]. These antigenic particles are highly immunogenic and immunostimulatory [18], [19].
Controlled pen trials showed that the vaccine is able to
Conclusion
The results summarized in this report demonstrate the feasibility of employing the vaccination with Gavac for the control of Boophilus infestations, resulting in the reduction of the acaricide-associated drawbacks with important savings for the cattle industry.
Acknowledgements
The authors wish to thank members of the Mammalian Cell Genetics and Technological Development Divisions and the group for the production of Gavac (Centro de Ingenierı́a Genética y Biotecnologı́a, Havana, Cuba) for fruitful discussions. Drs N. Costanza Vargas (Colombia) and J. Lona and V. Hernández (Mexico) are acknowledged for supplying unpublished results. Farm honors, researchers and national authorities from Cuba, Colombia, Brazil, Mexico and Iran are acknowledged for support and technical
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Gavac is a trade mark of Heber Biotec S.A. (P.O. Box 6162, Havana, Cuba).