Viral Diseases of Cattle

Cattle are susceptible to various viral diseases that significantly affect their health, productivity, and the economy.

1. Foot-and-Mouth Disease (FMD)

• Causative Agent: Foot-and-mouth disease virus (FMDV)
• Family: Picornaviridae
• Genus: Aphthovirus
• Transmission
  • Direct contact: Saliva, milk, or vesicular fluid.
  • Aerosolized droplets over long distances.
  • Contaminated equipment or personnel.
• Replication Cycle
  • Entry through mucosal surfaces → Replicates in the cytoplasm → Rapid lysis of host cells → Virus release.
• Pathogenesis
  • Virus infects epithelial cells of the mouth, feet, and udder → Vesicle formation → Rupture leads to ulceration.
• Clinical Signs
  • Fever, vesicles in the mouth, interdigital space, and teats, lameness, and salivation.
• Control
  • Vaccination, movement control, and strict biosecurity.

2. Bovine Viral Diarrhea (BVD)

• Causative Agent: Bovine viral diarrhea virus (BVDV)
• Family: Flaviviridae
• Genus: Pestivirus
• Transmission:
  • Direct contact: Nasal or oral secretions, milk, or semen.
  • Transplacental infection.
• Replication Cycle
  • Cytoplasmic replication; virion assembly occurs in the endoplasmic reticulum.
• Pathogenesis
  • Acute infection → Immunosuppression → Secondary infections; persistent infection in calves if transplacentally infected.
• Clinical Signs
  • Diarrhea, fever, oral ulcers, immunosuppression, and poor growth.
• Control
  • Vaccination, culling persistently infected animals, and biosecurity.

3. Infectious Bovine Rhinotracheitis (IBR)

• Causative Agent: Bovine herpesvirus-1 (BHV-1)
• Family: Herpesviridae
• Genus: Varicellovirus
• Transmission:
  • Aerosol droplets, direct contact, and genital secretions.
• Replication Cycle
  • Nuclear replication with latency in sensory ganglia.
• Pathogenesis
  • Infects respiratory and genital mucosa → Local inflammation → Immunosuppression.
• Clinical Signs
  • Fever, nasal discharge, conjunctivitis, dyspnea, and abortions.
• Control
  • Modified live or killed vaccines and biosecurity.

4. Bovine Respiratory Syncytial Virus (BRSV)

• Causative Agent: Bovine respiratory syncytial virus (BRSV)
• Family: Paramyxoviridae
• Genus: Orthopneumovirus
• Transmission
  • Aerosolized droplets and direct contact.
• Replication Cycle:
  • Cytoplasmic replication; formation of syncytial cells.
• Pathogenesis:
  • Infects respiratory epithelial cells → Syncytia formation → Interstitial pneumonia.
• Clinical Signs:
  • Cough, nasal discharge, dyspnea, and fever.
• Control:
  • Vaccination and good management practices.

5. Bovine Leukemia (Enzootic Bovine Leukosis)

• Causative Agent: Bovine leukemia virus (BLV)
• Family: Retroviridae
• Genus: Deltaretrovirus
• Transmission:
  • Direct blood contact, needles, and colostrum.
• Replication Cycle
  • Reverse transcription integrates viral genome into the host DNA.
• Pathogenesis
  • Infects B lymphocytes → Persistent infection → Tumor development.
• Clinical Signs
  • Enlarged lymph nodes, weight loss, and decreased production.
• Control
  • Test and cull infected animals; avoid blood contamination.

6. Rift Valley Fever (RVF)

• Causative Agent: Rift Valley fever virus (RVFV)
• Family: Phenuiviridae
• Genus: Phlebovirus
• Transmission
  • Mosquito vectors and contact with infected tissues.
• Replication Cycle:
  • Cytoplasmic replication; budding into Golgi vesicles.
• Pathogenesis
  • Viremia → Liver and spleen necrosis → Hemorrhagic disease.
• Clinical Signs
  • Fever, abortions, hemorrhages, and high mortality in young calves.
• Control
  • Vaccination, vector control, and movement restrictions.

7. Lumpy Skin Disease (LSD)

• Causative Agent: Lumpy skin disease virus (LSDV)
• Family: Poxviridae
• Genus: Capripoxvirus
• Transmission
  • Biting insects (flies, mosquitoes), direct contact, and fomites.
• Replication Cycle
  • Cytoplasmic replication; virions released by budding.
• Pathogenesis
  • Virus invades lymph nodes → Viremia → Skin and organ lesions.
• Clinical Signs
  • Skin nodules, fever, lameness, and reduced milk yield.
• Control
  • Vaccination and vector control.

General Control Measures for Viral Diseases in Cattle

1. Vaccination
   • Regular immunization based on disease prevalence.
2. Biosecurity
   • Limit animal movement, maintain farm hygiene, and isolate new or sick animals.
3. Vector Control
   • Use insecticides and manage breeding sites.
4. Surveillance and Testing
   • Monitor for disease outbreaks and test animals regularly.
5. Education
   • Train farmers and workers on recognizing signs and maintaining biosecurity.