Bovine viral diarrhea

Lore & Background

BVDV is a small, spherical, enveloped RNA virus of 40 to 60 nm in diameter. Its genome is a single linear positive-sense RNA molecule of about 12.3 kb, and RNA synthesis is catalyzed by a viral RNA-dependent RNA polymerase that can undergo template strand switching. Two genotypes are recognized based on the 5' untranslated region: BVDV-1 and BVDV-2, with BVDV-1 predominant worldwide and BVDV-2 representing a smaller proportion of cases in Europe (often less than 5%) and variable proportions in North America. Strains are further divided into cytopathic and non-cytopathic biotypes; the majority of field infections are caused by the non-cytopathic biotype.

Reader's Guide

Bovine viral diarrhea is considered one of the most significant infectious diseases in the livestock industry worldwide due to its high prevalence, persistence, and clinical consequences. In Europe, the prevalence of antibody-positive animals in countries without systematic control is between 60 and 80%. The disease causes a wide range of clinical signs including fertility issues, milk drop, pyrexia, diarrhea, and fetal infection, as well as immunosuppression that perpetuates other infectious diseases. The cornerstone of BVD's success is the persistently infected animal, which continuously sheds large quantities of virus. Countries that have failed to implement control or eradication programs have the highest PI prevalence. Diagnostic methods include antigen ELISA and rtPCR on ear tissue or serum samples, with repeat testing required to distinguish acute from persistent infection. Bulk tank milk testing can detect PI cows contributing to the tank.

Did You Know?

• PI animals shed a viral load one thousand times that of acutely infected animals.
• Estimates from specific studies suggest that around 20% of persistently infected animals survive to two years of age.
• Mucosal disease only develops in PI animals and is invariably fatal.
• BVDV can persist in the environment for more than two weeks.