Biochemical, immunological identification, characterization and localization of protective antigens, derived from the midgut of the tick amblyomma variegatum

Abstract

Tick infestation is a major problem in livestock industry. Ticks are vectors of parasites that cause devastating, often fatal diseases in livestock. In addition to diseases they transmit, ticks cause severe damage due to failure of cattle to achieve expected weight gains and damage to hides to be used for leather. Estimates of economic losses due to ticks and tick-borne diseases are in the billion of dollars worldwide. In Afiica, ticks and tick-borne diseases (TTBD) are particularly important and they are considered the greatest animal disease problem Tick control is heavily dependent upon chemical toxicants (acaricides). To date, some tick strains have become resistant to the available acaricides and the high cost of developing acaricides is prohibitive to the emergence of new ones. Immunization against ticks offers promising opportunities for tick control without the dangers inherent in the use of toxicants. This project investigated the possibility of identifying vaccine candidate( s) (antigens) that would protect the immunized animals against tick infestation. Midgut membrane proteins were isolated from the tick A. variegatum by use of a detergent (TX-114). Three protein fractions were obtained namely, proteins within the cytosol of'the disruptured cell (SOL fraction), DET fraction (integral proteins) and AQ fraction (peripheral proteins). The DET and the AQ fractions were used in this study to immunize rabbits in order to investigate their efficacy as vaccine candidates in immune protection againstA. variegatum. On SDS-PAGE (5-20%) and lmmunoblot analysis, 3 proteins with M,. 95,86 and 28 kDs from the DET fraction and two proteins witlrM, 66.5. and 53 kDs from the AQ fraction were found to be immunogenic. These proteins (except the 86,kDs protein) were also established as glycoproteins since they bound to con A affinity column. On immunoblots of2-Dimensional gel electrophoretic analysis of theAQandDET fractions, the immunogenic proteins were found to be acidic in nature. When DET fractionwas loaded on immunoaffinity column prepared using purified IgG from the anti-DET sera, the 3 proteinsmentioned above with M, 95,86 and 28 kDs were bound. This study has named these immunogenicproteins as Av-D95, Av-D86 and Av-D28 from the DET fraction and Av-A66.5 and Av-A53from the AQ fraction. A Comparison of the tick midgut protein fractions from the field strains with the laboratory strainderivedfractions using SDS-PAGE (5-20%) showed some differences in both the SOL and AQ fractionswhile the DET fractions appeared to have the same protein composition. By immunoblot analysis,most of the immunogenic proteins were shared between the strains. The level of protection of the immunized rabbits was assessed by measuring the engorgement weights of female adults, egg batch weights and percentage hatchability (viability). Female engorgementweights were reduced by 25% and 20% when fed on rabbits immunized with DET phase and AQ phase respectively. The percent hatchability of the eggs laid by ticks infested on rabbits immunizedwith DET phase antigens was 14.29% while that of eggs laid by ticks infested on rabbits immunizedwith AQ phase antigens.was 33.04 %. Eggs from the control gave percentage hatchability of 62.64 %., By considering all the assessed parameters, the reproductive capacity of the ticks was foundto be reduced by 77% and 48% when the DET and AQ fractions were used to immunize rabbits respectively. Therefore, this study was able to establish t6at its possible to immunize animals against the tick A. variegatum. However, more work is imperative for the full development of the vaccine againstthe tick species.