Characterization of Immune Function in Juvenile BVDV PI Alpacas (Part 1)

Principal investigators:

Bedenice D., Davis W., Hamilton MJ, Dubovi E, Costa L
Tufts Cummings School of Veterinary Medicine, Washington State University, Cornell Diagnostic Laboratory

Study objective: To characterize the clinical and immunological characteristics of persistent BVDV infection and determine its effect on in-vitro lymphocyte proliferation, circulating B and T cell populations, complete blood count and immunoglobulins in alpacas.

Animals: 12 persistently infected alpaca crias, identified via sequential PCR and virus isolation.

Results: The mortality of PI alpacas reached 58% by 6 months of age and was most consistently associated with marked weight loss. Flow cytometry on 9 different PI (sampled at multiple time points) vs. 35 age matched control alpacas demonstrated a significant monocytosis and T-cell depletion, with specific reduction in CD4 cells (T-helper cells). Monocyte infection is expected to reduce their capacity to stimulate T-cell proliferation, an integral component of both cell-mediated and antibody-mediated immunity against BVDV. Infected alpacas further suffered from significant anemia and hypoproteinemia, with a reduction in albumin and increased α2 globulin fraction on serum protein electrophoresis.

Prolonged viremia (chronic BVDV infection) vs. Persistent Infection: Since 2005, three crias with extended viremia (chronic infection) have been identified by the authors. These animals demonstrated prolonged viral shedding (>56 days, > 67 days and >250 days) following perinatal (n=1) as well as intra-uterine BVDV infection (n=2). In the presence of maternal BVDV antibodies, a definitive differentiation between chronic and persistent BVDV infection may not be possible until virus-specific humoral responses with production of neutralizing antibodies become apparent (at > 6 months in some chronically infected alpacas). Both PI and chronically infected alpacas show similar evidence of immune suppression, associated with T-cell depletion.

Daniela Bedenice, Dr. med. vet., Dipl. ACVIM, Dipl ACVECC, Assistant Professor, Cummings School of Veterinary Medicine at Tufts University. Daniela.bedenice@tufts.edu Tel: 508 839 7926, Fax: 508 839 7931