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Title: Thrombostasin isoform frequency in a Central Texas field population of the horn fly, Haematobia irritans

item Olafson, Pia
item Pruett Jr, John
item Atteberry, Heather

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2006
Publication Date: 12/20/2006
Citation: Olafson, P.U., Pruett Jr, J.H., Atteberry, H.N., Steelman, C.D. 2006. Thrombostasin isoform frequency in a Central Texas field population of the horn fly, Haematobia irritans. Veterinary Parasitology. 142:359-366.

Interpretive Summary: The horn fly remains the leading economically important insect pest of cattle, costing an estimated loss of $800 million annually to North American producers. The horn fly is a blood-feeding parasite that utilizes a factor in the saliva that prevents coagulation of host blood by inhibiting thrombin, an important factor in the blood coagulation cascade. That factor has been identified and is called thrombostasin. Blocking of thrombostasin activity with a vaccine has been proposed as a novel, non-chemical control strategy. We have analyzed the occurrence of various forms of thrombostasin in a population of horn flies collected from Camp Stanley, Texas in an effort to describe potential differences in thrombostasin from horn flies of different geographic regions, which may affect vaccine efficacy. In addition, a difference in the distribution of TS forms was found in flies from bull calves that were characterized as high- or low-carriers of horn flies. This may suggest that there is an association between a particular TS form and the host thrombin molecule. Future studies of thrombin variants from high- and low-carriers may define those associations and, in fact, may identify a host genetic marker for selective breeding of cattle that are low-carriers for horn flies.

Technical Abstract: Thrombostasin is an anti-thrombin factor that plays a role in successful feeding of the horn fly, Haematobia irritans. It has been isolated and characterized from saliva, and polymorphisms in the gene coding sequence have been previously reported. In the present study, the TS gene was analyzed from 104, field-collected flies from Camp Stanley, Texas (CS-TX) and the allele and genotype frequencies were compared with previously published data for an Alabama field collection and an in vitro colony-reared collection. Significant differences in genotype frequency and extent of genotypic diversity between these three populations were observed, and may be attributable to host genetic differences. In addition, differences in genotype distribution were observed between flies collected from bull calves that were either high- or low-carriers of horn flies, supporting a possible explanation for horn fly host selection behavior.