Bovine viral diarrhea

Bovine Viral Diarrhea (BVD) is a contagious disease affecting cattle worldwide. It is caused by the Bovine Viral Diarrhea Virus (BVDV), which belongs to the genus Pestivirus within the family Flaviviridae. The disease manifests in various forms, ranging from subclinical to acute and severe, and can lead to significant economic losses in the cattle industry due to decreased milk production, reproductive disorders, and increased mortality rates.

Etiology

BVD is caused by two biotypes of the virus: the noncytopathic and the cytopathic. These biotypes differ in their effect on infected cells but both can cause disease in cattle. The virus is highly variable, with two main genotypes identified: BVDV-1 and BVDV-2, each comprising several subtypes.

Transmission

The primary mode of transmission is through direct contact with infected animals. The virus can be found in various bodily fluids such as blood, saliva, milk, and semen, facilitating its spread within herds. Indirect transmission can occur via contaminated equipment, clothing, and through the use of biological products derived from infected animals. Additionally, the virus can cross the placenta, infecting the fetus and leading to the birth of persistently infected (PI) calves, which serve as a major reservoir for the virus.

Clinical Signs

The clinical signs of BVD vary widely. Acutely infected animals may exhibit fever, lethargy, decreased appetite, nasal and ocular discharges, diarrhea, and, in severe cases, death. Reproductive issues such as abortion, congenital abnormalities, and infertility can also occur. PI animals may appear normal or show signs of poor growth and chronic ill health.

Diagnosis

Diagnosis of BVD involves a combination of clinical signs, virus isolation, and serological tests. Polymerase Chain Reaction (PCR) and Enzyme-Linked Immunosorbent Assay (ELISA) are commonly used to detect the presence of the virus or antibodies against it. Identifying PI animals is crucial for controlling the spread of the disease within herds.

Prevention and Control

Effective control of BVD requires a comprehensive approach, including biosecurity measures, vaccination, and the identification and removal of PI animals from the herd. Vaccines are available and widely used to prevent BVD; however, vaccination alone cannot eliminate the disease without additional management practices. Regular testing and maintaining a closed herd are also important strategies in preventing the introduction and spread of BVD.

Economic Impact

The economic impact of BVD on the cattle industry is significant, with losses stemming from decreased productivity, increased veterinary costs, and the need for additional labor to manage outbreaks. The cost of preventive measures, although substantial, is generally considered to be lower than the losses associated with the disease.