While vital research continues, veterinarians know quite a bit about the group of clinical diseases known as bovine viral diarrhea (BVD), the viruses that cause it and how to prevent or control it in beef and dairy herds. Despite research progress and widespread vaccination and testing BVD continues to cause substantial losses across the production chain.
Julia Ridpath, PhD, recently retired after studying BVDV and related pestiviruses at the USDA’s National Animal Disease Center (NADC) in Ames, Iowa. She has authored or co-authored over 200 research papers, mostly on BVD and related diseases in cattle. Ridpath co-edited the book "BVDV: Diagnosis, Management, and Control", and led a research project at NADC titled "Intervention Strategies to Control Viral Diseases of Cattle."
Ridpath says three species of pestiviruses cause BVD disease worldwide; bovine viral diarrhea type 1 BVDV1), BVDV2 and HoBi-like viruses. BVDV1 and BVDV2 are found nearly worldwide, while HoBi-like viruses occur primarily in Asia, South America and somewhat in Europe. While HoBi-like viruses have not been identified in U.S. herds, Ridpath encourages producers, veterinarians and diagnostic labs to monitor BVD cases for the causative agent.
Ridpath stresses that effective BVDV control requires three components: diagnosis, vaccination and biosecurity.
Diagnosis presents challenges because there is no single “typical” BVD presentation. Cases can be from mild to severe, and veterinarians cannot rely on herd history, clinical presentations or post-mortem exams alone to diagnose the disease. Accurate diagnosis requires laboratory testing, ideally on two samples submitted about three weeks apart.
Disease syndromes associated with BVD include immunosuppression, reproductive disease, mucosal disease, enteric disease and persistently infected (PI) calves, which sometimes show little or no clinical sign of disease.
PI calves occur when the dam is exposed to BVDV1, BVDV2 or HoBi-like viruses during the first trimester of gestation. Many are sickly and do not survive long, but some others show little or no signs of disease and shed the virus continuously, exposing the rest of the herd. Diagnosis, removal and isolation of PI cattle serves as a critical step in a BVDV-control program.
While BVD receives deserved attention as a reproductive disease, Ridpath expresses concern over the effect of infection on neonates. In exposed calves, the viruses that cause BVD can affect the thymus and disrupt maturation of the immune system, potentially with long-term health effects.
Note: This article originally appeared as a part of "BVD Control: Multi-pronged approach" in the March 2017 issue of Bovine Veterinarian.