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.