Two initial vaccinations with the Bm86-based Gavac vaccine against Rhipicephalus (Boophilus) microplus induce similar reproductive suppression to three initial vaccinations under production conditions

Background: The cattle tick, Rhipicephalus (Boophilus) microplus, affects livestock production in many regions of the world. Up to now, the widespread use of chemical acaricides has led to the selection of acaricide-resistant ticks and to environmental contamination. Gavac is a subunit vaccine based on the recombinant Bm86 tick antigen expressed in yeast, capable to control infestations of R. microplus under controlled and production conditions. The vaccine constitutes the core element of broad control programs against this ectoparasite, in which acquired immunity in cattle to Bm86 is combined with a rational use of acaricides. At present, the conventional vaccine scheme consists of three doses that should be administered at weeks 0, 4 and 7, followed by a booster every six months. Results: In this study we assayed a reduction in the number of the initial doses of Gavac, evaluated the time course and the level of bovine anti-Bm86 antibodies elicited, and analyzed the vaccine effect on ticks engorging on immunized cattle under production conditions. Following three different immunization schemes, the bovines developed a strong and specific immune response characterized by elevated anti-Bm86 IgG titers. A reduction in the weight of engorging female ticks, in the weight of the eggs laid and also in R. microplus viable eggs percentage was obtained by using only two doses of Gavac administered at weeks 0 and 4, followed by a booster six months later. This reduction did not differ from the results obtained on ticks engorging on cattle immunized at weeks 0, 4 and 7. It was also demonstrated that anti-Bm86 antibody titers over 1:640, measured in bovines immunized at weeks 0 and 4, were sufficient to affect weight and reproductive potential of female ticks as compared with ticks engorging on unvaccinated animals. In addition, no statistically significant differences were detected in the average weight of eggs laid by ticks engorged on immunized cattle that showed anti-Bm86 specific titers in the range of 1:640 to 1:81920. Conclusion: The administration of two initial doses of Gavac containing 100 μg of Bm86 antigen to nonimmunized cattle under production conditions is sufficient to affect the weight and the reproductive capacity of R. microplus engorging females. According to these results, cattle herds’ manipulation and vaccine costs could be potentially reduced with a positive impact on the implementation of integrated control programs against R. microplus. * Correspondence: [email protected] Animal Health Department, Center for Genetic Engineering and Biotechnology, 31th Avenue and 190, Havana, 10600, Cuba Full list of author information is available at the end of the article Vargas et al. BMC Veterinary Research 2010, 6:43 http://www.biomedcentral.com/1746-6148/6/43 © 2010 Vargas et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background Rhipicephalus microplus is an ectoparasite that currently affects the cattle industry in many regions of the world and it is also an important vector for the transmission of parasites in diseases such as anaplasmosis and babesiosis [1,2]. The use of acaricides is the most extended prophylactic and therapeutic method to control ectoparasites. However, some relevant drawbacks regarding their use are the development of acaricide-resistant ticks after repeated treatments, the chemical contamination of cattle-derived products and of the environment [3-5]. In the last years, these factors led to the selection of alternative strategies aiming to achieve a better control of ectoparasites under safer approaches [6-8]. Efforts were primarily focused in the identification and characterization of concealed Bm86-like antigens as vaccine candidates [9-13]. Other tick antigens such as BmTI, serine protease inhibitors and 4D8 have been described in recent years with marked potential for the development of novel or combined vaccines [14-17]. However, only two Bm86-based vaccines commercially available have been used in the field in different countries involving the immunization and monitoring of a large number of bovines [18-21]. Nowadays, it is known that using Bm86 for cattle immunization turns into a highly effective control method if it is used as part of an integrated control program in which acaricides are simultaneously applied according to the infestation index detected [21,22]. The most remarkable benefits regarding the use of Bm86-derived vaccines are the reduction in reproductive capacity of engorging females and in the frequency of acaricide treatments. The implementation of such programs using Gavac implies an immunization scheme that starts with the administration of three doses at weeks 0, 4, and 7, followed by boosters every six months [22-24]. This method showed its effectiveness in the induction of high antibody titers in bovines in spite of their race, sex, or reproductive category [25]. However, this regimen demands an arduous manipulation of cattle herds in the first two months since treatment is performed. Therefore, the implementation of a different schedule that allows a reduction of manipulation and vaccine costs constitutes a desirable fact for both practical and commercial points of view. The Bm86 antigen contained in Gavac is obtained in a highly particulated form, with high homogeneity and reproducibility in P. pastoris yeast [26], under strict controls of a well-recognized biotechnology industry [8,27]. Taking into consideration that this antigen is immunogenically superior with regard to the monomeric form of the protein [28], this fact prompted us to investigate the capacity of two doses of the vaccine to elicit immune responses and tick damage similar to those achieved with the use of three inoculations. In this work, we demonstrated that the generation of specific antibodies and the physical damage caused to female ticks engorging on cattle immunized under production conditions remained invariable after reducing in one dose the number of initial administrations of the Gavac vaccine.