Vaccination with recombinant tick antigens for the control of Ixodes scapularis adult infestations.

Antigens protective against Ixodes scapularis infestations were identified by cDNA expression library immunization (ELI) and analysis of expressed sequenced tags (EST). Three cDNAs protective against larval tick infestations, 4F8, with homology to a nucleotidase, and 4D8 and 4E6 of unknown function, were characterized and obtained as recombinant proteins for immunization studies. Vaccination trials with recombinant proteins demonstrated an effect of these antigens against I. scapularis larvae in a mouse model. Herein, we evaluated the effect of recombinant antigens on I. scapularis adult infestations on immunized sheep. Vaccination with recombinant 4D8, 4F8, 4E6 and the combination of all three antigens reduced adult tick infestations by 58, 12, 20, and 16%, respectively, when compared to the control group but was statistically significant for 4D8 and 4F8 only. Oviposition was reduced by 22-49% in all groups immunized with recombinant tick antigens (P<0.05). The overall efficacy of vaccine formulations considering the effect on tick infestations and oviposition averaged 33-71%. These antigens, and especially 4D8, appear to be good candidates for continued development of a vaccine for control of tick infestations.