Association between the strength of serologic recognition of bovine leukosis virus and lymphocyte count in bovine leukosis virus-infected cows

Dusty W. Nagy Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802.

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 DVM, MS, DACVIM
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Jeff W. Tyler Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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Aaron Stoker Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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Steven B. Kleiboeker Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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 DVM, PhD, DACVM

Abstract

Objective—To determine whether strength of serologic recognition of bovine leukosis virus (BLV) by use of ELISA is associated with blood lymphocyte counts.

Design—Prospective study.

Animals—161 cows with positive results of ELISA for BLV.

Procedure—Sample-to-positive ratio (S:P), which is the ratio between the test sample and a positive control sample, was compared among lymphocytotic and nonlymphocytotic cows. A regression model was constructed to evaluate the association between blood lymphocyte concentration and S:P, age, and the interaction of these terms.

Results—Mean S:P differed significantly between lymphocytotic (2.58 ± 0.36) and nonlymphocytotic (2.38 ± 0.39) cows. Age and S:P were significantly associated with lymphocyte count.

Conclusions and Clinical Relevance—Sample-topositive ratio and lymphocyte count were related; however, cows with high S:P were not always lymphocytotic. Culling cows on the basis of S:P will reduce the herd load of infectious virus faster than random culling of ELISA-positive cows; however, culling on the basis of lymphocyte count will eliminate a greater proportion of the reservoir of infection. (J Am Vet Med Assoc 2002;220:1681–1684)

Abstract

Objective—To determine whether strength of serologic recognition of bovine leukosis virus (BLV) by use of ELISA is associated with blood lymphocyte counts.

Design—Prospective study.

Animals—161 cows with positive results of ELISA for BLV.

Procedure—Sample-to-positive ratio (S:P), which is the ratio between the test sample and a positive control sample, was compared among lymphocytotic and nonlymphocytotic cows. A regression model was constructed to evaluate the association between blood lymphocyte concentration and S:P, age, and the interaction of these terms.

Results—Mean S:P differed significantly between lymphocytotic (2.58 ± 0.36) and nonlymphocytotic (2.38 ± 0.39) cows. Age and S:P were significantly associated with lymphocyte count.

Conclusions and Clinical Relevance—Sample-topositive ratio and lymphocyte count were related; however, cows with high S:P were not always lymphocytotic. Culling cows on the basis of S:P will reduce the herd load of infectious virus faster than random culling of ELISA-positive cows; however, culling on the basis of lymphocyte count will eliminate a greater proportion of the reservoir of infection. (J Am Vet Med Assoc 2002;220:1681–1684)

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