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Summary

Each of 5 US-origin serotypes of bluetongue virus (btv) was inoculated into a separate pair of sheep. The duration of each animal's ensuing viremia was monitored, using a btv serogroup-specific nested polymerase chain reaction (pcr) method and an embryonating chicken egg (ece) inoculation procedure. Mean duration of viremia was 100 and 38 days for the pcr and ece methods, respectively. This difference was significant (P < 0.001) and documents a more prolonged viremia in virus-exposed sheep than has been reported. A dual internal oligonucleotide solution hybridization procedure was developed for the rapid (2 hours) colorimetric detection and identification of btv-specific pcr products. This enzyme-linked oligonucleotide sorbent assay (elosa) relied on annealing of separate biotinylated and fluores-ceinated probes to the amplified btv nucleic acid; these complexes were captured on streptavidin-coated microtitration wells and were detected, using a horseradish peroxidase-labeled antifluorescein antibody conjugate. End-point dilution analyses of pcr products indicated that the elosa was more sensitive than gel electrophoretic or comparable colorimetric slot-blot hybridization techniques. The btv pcr-elosa system represents a more sensitive and expeditious means of diagnosing btv-induced viremia than does the ece procedure currently used. The combination of elosa with pcr should facilitate practical application of nucleic acid technology to diagnostic veterinary medicine.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate herd-level risk factors for seropositive status of cattle to 1 or more bluetongue viruses.

Animals—110 herds of cattle in Nebraska, North Dakota, and South Dakota.

Procedure—Blood samples were collected before and after the vector season. Samples were tested for antibodies against bluetongue virus by use of a commercially available competitive ELISA. Factors evaluated included descriptors of geographic location and management practices. Trapping of insect vectors was conducted to evaluate vector status on a subset of 57 operations. A multivariable logistic regression model was constructed to evaluate associations.

Results—For the full data set, altitude and latitude were associated with risk of having seropositive cattle (an increase in altitude was associated with an increase in risk, and a more northerly location was associated with a decrease in risk of a premise having seropositive cattle). Import of cattle from selected states was associated with an increase in risk of having seropositive cattle. From the subset of herds with data on vector trapping, altitude and latitude were associated with risk of having seropositive cattle, similar to that for the full model. However, commingling with cattle from other herds was associated with a decrease in risk of seropositivity.

Conclusions and Clinical Relevance—Findings reported here may be useful in generating additional hypotheses regarding the ecologic characteristics of bluetongue viruses and other vector-borne diseases of livestock. Sentinel surveillance programs are useful for documenting regionalization zones for diseases, which can be beneficial when securing international markets for animals and animal products. (Am J Vet Res 2005;66:853–860)

Full access
in American Journal of Veterinary Research