Salivary gland thrombostasin isoforms differentially regulate blood uptake of horn flies fed on control- and thrombostasin-vaccinated cattle

Thrombostasin (TS) is an anticlotting protein found in saliva of Haematobia irritons (horn flies). The polymorphic nature of the ts gene was first associated with success of horn flies blood feeding on a laboratory host, New Zealand White rabbits. In this study, we report results of similar studies testing blood uptake of horn flies feeding on a natural host, cattle. These studies confirmed the association of ts genotype with blood uptake of horn flies and showed that it was host species specific. In contrast to rabbits, blood uptake volumes of homozygous ts10 horn flies were lower than those of other ts genotypes when fed on control (ovalbumin-vaccinated) cattle. Cattle vaccinated with recombinant protein isoforms, rTS9 or rTB8, resisted horn fly feeding by yielding lower blood volumes compared with flies feeding on control cattle. The specific impact of vaccination, however, varied by ts genotype of flies, Cattle vaccinated with isoform rTS9 resisted flies of ts2, ts9, and tb8 genotype. Vaccination with isoform rTB8 produced resistance to ts8, ts9, and tb8 genotype flies. Horn flies of genotype ts10 were not affected by vaccination with either TS isoform and fed as well on rTS9- and rTB8-vaccinated as on control-vaccinated cattle. These experimental results confirm the efficacy of vaccines targeting horn fly salivary proteins and provide new insight into the dynamics of horn fly-cattle interactions in nature. © 2010 Entomological Society of America

Salivary gland thrombostasin isoforms differentially regulate blood uptake of horn flies fed on New Zealand white rabbits

Thrombostasin (TS) is a previously characterized anticlotting protein with multiple isoforms found in the saliva of horn flies. In this report, the effect of TS isoforms on blood feeding was assessed using individual flies that carried corresponding ts allelles. Laboratory studies of horn fly blood feeding were conducted using colony-reared flies fed on New Zealand White (NZW) rabbits. After timed 20-min feeding periods, each fly was characterized for gender, blood volume uptake, and ts genotype. The results showed that mean blood volumes obtained by individual flies were not related to fly gender but were correlated to the ts genotype(s) carried by each fly. A fly having one or both ts alleles coding for the TS9 isoform took less blood than those possessing one or both ts alleles coding for the TS10 isoform. These results confirm the significant role that TS plays in horn fly feeding and highlight the differential impact of TS protein isoforms that vary by as few as three amino acids. © 2009 Entomological Society of America

Evaluation of a recombinant salivary gland protein (thrombostasin) as a vaccine candidate to disrupt blood-feeding by horn flies

The potential for controlling blood-feeding by the cattle pest, Haematobia irritans irritans (horn fly), was tested by vaccination against thrombostasin (TS), an inhibitor of mammalian thrombin that is released into skin during horn fly blood-feeding. The increase in blood meal size that occurred for flies feeding on sensitized non-vaccinated hosts was blocked and egg development in female flies was delayed when horn flies fed on rabbits and cattle immunized with recombinant TS. This demonstration of the impact of disrupting TS action by vaccination provides a novel approach toward control of this veterinary pest and offers a paradigm for limiting blood-feeding in other medically-important insect species. © 2003 Elsevier Ltd. All rights reserved