Prevalence, outcome, and health consequences associated with persistent infection with bovine viral diarrhea virus in feedlot cattle.

OBJECTIVE: To estimate prevalence of cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) at arrival at a feedlot, prevalence of chronically ill and dead PI cattle, and the magnitude of excess disease attributable to a PI animal.
DESIGN: Cross-sectional and cohort studies. ANIMALS: 2,000 cattle at the time they arrived at a feedlot, 1,383 chronically ill cattle from 7 feedlots, and 1,585 dead cattle from a single feedlot. PROCEDURE: Skin biopsy specimens were collected and evaluated via immunohistochemistry. Cattle were characterized as either PI or not PI with BVDV on the basis of characteristic immunostaining. Follow-up was obtained for the 2,000 cattle from which samples were collected at arrival, and health outcomes were determined for cattle exposed and not exposed to a PI animal.
RESULTS: Prevalence of PI cattle was 0.3% at arrival, 2.6% in chronically ill cattle, and 2.5% in dead cattle. Risk of initial treatment for respiratory tract disease was 43% greater in cattle exposed to a PI animal, compared with those not exposed to a PI animal. Overall, 15.9% of initial respiratory tract disease events were attributable to exposure to a PI animal. CONCLUSIONS AND CLINICAL RELEVANCE: Relatively few PI cattle arrive at feedlots. However, those cattle are more likely to require treatment for respiratory tract disease and either become chronically ill or die than cattle that are not PI. In addition, they are associated with an increase in the incidence of respiratory tract disease of in-contact cattle.