Objective—To estimate seroprevalence of antibodies against bovine viral diarrhea virus (BVDV) and incidence of seroconversion in alpacas in the United States during 2006 to 2007 and to evaluate associations between BVDV seropositive status and potential risk factors for exposure to BVDV.

Design—Cross-sectional and longitudinal cohort study.

Sample—Blood samples from 192 alpacas > 6 months old in 39 herds from 20 states; 40 owners who completed questionnaires.

Procedures—550 US alpaca owners, stratified by state and randomly selected from a list of approximately 4,300 owners, were mailed a study description, voluntary participation request, and questionnaire. Thirty-nine owners submitted blood samples from up to 6 alpacas > 6 months old; 27 of 39 owners submitted another blood sample from the same alpacas > 1 month later. Samples were tested for serum virus-neutralizing antibodies against BVDV. Seropositive status was used to indicate BVDV exposure. Associations between seropositive status and potential risk factors for BVDV exposure described in questionnaires were evaluated by use of a Fisher exact test.

Results—8 of 192 (4.2%) alpacas in 3 of 39 (7.7%) herds were seropositive. Larger herds had a greater percentage of seropositive alpacas than did smaller herds. No alpaca from which a second blood sample was obtained seroconverted during 292 to 1,460 alpaca-days (mean, 740 alpaca-days) of potential exposure.

Conclusions and Clinical Relevance—Results contributed to information on assessment of BVDV prevalence, risk factors for exposure, and alpaca industry practices in 2006 to 2007 during the emergence of BVDV as a major disease in alpacas.