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Bovine Viral Diarrhea (BVD) in Cattle


Introduction

Bovine Viral Diarrhea (BVD) is a globally significant viral disease of cattle characterized by a wide range of clinical manifestations, including reproductive failure, immunosuppression, respiratory disease, and gastrointestinal signs. The disease is particularly important due to the role of persistently infected (PI) animals in maintaining and spreading infection within herds.

Etiology
Causative Agent

BVD is caused by Bovine Viral Diarrhea Virus (BVDV), a member of the genus Pestivirus in the family Flaviviridae.

Virus Types
  • BVDV-1 and BVDV-2: Two major genotypes
  • Cytopathic (CP) strains: Cause visible cell damage in culture
  • Non-cytopathic (NCP) strains: Most common; responsible for persistent infections
Virus Characteristics
  • Enveloped, single-stranded positive-sense RNA virus
  • Moderately fragile in the environment
  • Inactivated by disinfectants and heat
Epidemiology
Species Affected
  • Cattle (primary host)
  • Other ruminants (sheep, goats, deer) may be infected
Transmission
  • Direct contact with infected animals
  • Exposure to secretions (nasal discharge, saliva, feces, urine)
  • Vertical (transplacental) transmission
  • Contaminated equipment, needles, and biological products
Persistently Infected (PI) Animals
  • Infected in utero with NCP strains during early gestation
  • Immunotolerant and shed virus continuously throughout life
  • Major source of infection in herds
Risk Factors
  • Introduction of PI animals
  • Poor biosecurity
  • Commingling of herds
  • Inadequate vaccination programs
Pathogenesis
Acute Infection

Following entry via the respiratory or oral route, the virus replicates in lymphoid tissues, leading to viremia and systemic spread.

Immunosuppression
  • Destruction of lymphoid tissue
  • Increased susceptibility to secondary infections
Persistent Infection
  • Occurs when fetus is infected between ~40–120 days of gestation
  • Fetus recognizes virus as “self” and fails to mount an immune response
Mucosal Disease
  • Occurs in PI animals infected with a CP strain or mutation of NCP strain
  • Severe, often fatal disease with erosive lesions
Clinical Signs
Subclinical Infection
  • Most infections are mild or inapparent
Acute BVD
  • Fever
  • Depression
  • Nasal discharge
  • Mild diarrhea
  • Reduced milk production
Reproductive Effects
  • Early embryonic death
  • Abortion
  • Congenital defects (e.g., cerebellar hypoplasia)
  • Birth of persistently infected calves
Mucosal Disease
  • Severe diarrhea (often bloody)
  • Oral and gastrointestinal erosions
  • Dehydration
  • High mortality
Respiratory Disease
  • Part of bovine respiratory disease complex (BRD)
  • Coughing and pneumonia due to secondary infections
Summary for Practitioners

BVD should be suspected in herds with reproductive failure, immunosuppression, or unexplained disease outbreaks. Identification of PI animals is critical for control.

Postmortem Findings
Gross Lesions
  • Erosions and ulcers in oral cavity and gastrointestinal tract
  • Petechial hemorrhages
  • Enlarged lymph nodes
  • Pneumonia (in secondary infections)
Microscopic Lesions
  • Lymphoid depletion
  • Necrosis of epithelial tissues
  • Inflammation in affected organs
Diagnosis
Clinical Diagnosis

Based on clinical signs, herd history, and reproductive problems.

Laboratory Diagnosis
  • PCR for viral RNA detection
  • Antigen-capture ELISA (especially for PI animals)
  • Virus isolation
  • Serology (paired samples)
Testing for PI Animals
  • Ear notch testing (ELISA or PCR)
  • Repeat testing to confirm persistent infection
Differential Diagnosis
  • Infectious Bovine Rhinotracheitis (IBR)
  • Parainfluenza-3 virus
  • Bacterial enteritis
  • Other causes of reproductive failure
Summary for Practitioners

Accurate diagnosis and identification of PI animals are essential for effective herd control programs.

Treatment
General Approach

No specific antiviral treatment is available.

Supportive Care
  • Fluid therapy
  • Management of secondary infections (antibiotics)
  • Nutritional support
Summary for Practitioners

Treatment is supportive. Prevention and herd-level control strategies are far more effective than individual treatment.

Control and Prevention
Identification and Removal of PI Animals
  • Test and cull PI animals
  • Prevent introduction into herd
Vaccination
  • Modified-live and inactivated vaccines available
  • Important for breeding animals
Biosecurity
  • Test new animals before introduction
  • Control movement of animals and equipment
  • Avoid shared needles and equipment
Reproductive Management
  • Protect pregnant animals from exposure
  • Implement herd health programs
Summary for Practitioners

Effective control requires a combination of testing, culling PI animals, vaccination, and strict biosecurity.

Zoonotic Importance

BVD is not zoonotic and does not infect humans.

Economic Importance

BVD causes significant economic losses due to reproductive failure, decreased productivity, treatment costs, and control program expenses.

Summary

Bovine Viral Diarrhea is a complex disease of cattle with diverse clinical manifestations. Persistent infection plays a central role in transmission, making identification and removal of PI animals essential for control.