|OLDS, CASSANDRA - Washington State University|
|MWAURA, STEPHEN - International Livestock Research Institute (ILRI) - The Netherlands|
|ODONGO, DAVID - International Livestock Research Institute (ILRI) - The Netherlands|
|BISHOP, RICHARD - International Livestock Research Institute (ILRI) - The Netherlands|
|DAUBENBERGER, CLAUDIA - Swiss Tropical Institute(STI)|
Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2016
Publication Date: 9/2/2016
Citation: Olds, C.L., Mwaura, S., Odongo, D., Scoles, G.A., Bishop, R., Daubenberger, C. 2016. Induction of humoral immune response to multiple recombinant rhipicephalus appendiculatus antigens and their effect on tick feeding success and pathogen transmission. Parasites & Vectors. 9(1):484.
Interpretive Summary: The Brown Ear tick, Rhipicephalus appendiculatus infests cattle throughout large parts of central and southern Africa. East Coast fever (ECF) is a devastating disease of cattle that causes very high mortality in sub-Saharan Africa. ECF is caused by a parasite known as Theileria parva that is transmited only R. appendiculatus ticks. This disease has been particularly difficult to control due to many factors including the presence of a wildlife reservoir (African buffalo), the expense of tick control, and the increasing incidence of acaricide resistance. There have been numerous efforts to control ECF by controlling the ticks that transmit it, however vaccines targeting the tick have not previously been tested as a possible control strategy. In this work we have attempted to interrupt tick feeding and in so doing interfere with transmission by vaccinating cattle with a vaccine consisting of several tick antigens involved in tick feeding as well as a parasite antigen that is located on the surface of the infective stage. We hypothesized that the combination of these antigens might reduce tick feeding success and block transmission of the parasite. Although we were able to induce strong immune responses to the vaccine antigens in the vaccinated cattle there was no significant effect on tick feeding success or transmission of T. parva. However, this was the first attempt to use a natural tick-parasite-host transmission model to test the efficacy of candidate vaccine antigens and may serve as a model for future vaccine challenge systems.
Technical Abstract: Background: Rhipicephalus appendiculatus is the primary vector of Theileria parva, the etiologic agent of East Coast fever (ECF), a devastating disease of cattle in sub-Saharan Africa. We hypothesized that a vaccine targeting tick proteins that are involved in attachment and feeding might affect feeding success and possibly reduce tick-borne transmission of T. parva. Here we report the evaluation of a multivalent vaccine cocktail of tick antigens for their ability to reduce R. appendiculatus feeding success and possibly reduce tick-transmission of T. parva in a natural host-tick-parasite challenge model. Methods: Cattle were inoculated with a multivalent antigen cocktail containing recombinant tick protective antigen subolesin as well as two additional R. appendiculatus saliva antigens: the cement protein TRP64, and three different histamine binding proteins. The cocktail also contained the T. parva sporozoite antigen p67C. The effect of vaccination on the feeding success of nymphal and adult R. appendiculatus ticks was evaluated together with the effect on transmission of T. parva using a tick challenge model. Results: This is the first evaluation of the anti-tick effects of these antigens in the natural host-tick-parasite combination. In spite of evidence of strong immune responses to all of the antigens in the cocktail, vaccination with this combination of tick and parasite antigens did not appear to effect tick feeding success or reduce transmission of T. parva. Conclusion: The results of this study highlight the importance of early evaluation of anti-tick vaccine candidates in biologically relevant challenge systems using the natural tick-host-parasite combination