Viral Diseases of Sheep and Goats

Sheep and goats are susceptible to a variety of viral diseases, many of which have significant economic and health implications.

1. Peste des Petits Ruminants (PPR)

• Causative Agent: Peste des petits ruminants virus (PPRV)
• Family: Paramyxoviridae
• Genus: Morbillivirus

Transmission

• Direct contact via respiratory droplets and secretions.
• Indirect via contaminated feed and water.

Replication Cycle

• Enters cells via fusion with host membrane.
• Replicates in cytoplasm.
• Produces infectious virions that bud off.

Pathogenesis

• Virus targets lymphoid tissues, epithelium of respiratory and gastrointestinal tracts.
• Causes immunosuppression and epithelial damage.

Clinical Signs

• Fever, nasal discharge, coughing.
• Oral ulcers, diarrhea, and dehydration.
• High morbidity and mortality.

Control

• Vaccination with live attenuated PPRV vaccine.
• Quarantine and movement restrictions.

2. Sheep and Goat Pox (SGP)

• Causative Agent: Sheep pox virus (SPPV) and Goat pox virus (GTPV)
• Family: Poxviridae
• Genus: Capripoxvirus

Transmission

• Direct contact with infected animals or scabs.
• Aerosols and fomites.

Replication Cycle

• Replicates in cytoplasm, forming intracytoplasmic inclusions.

Pathogenesis

• Virus replicates in skin and respiratory tissues, leading to viremia and systemic spread.

Clinical Signs

• Fever, skin lesions, and respiratory distress.
• High mortality in young animals.

Control

• Live attenuated vaccine.
• Biosecurity and insect control.

3. Bluetongue

• Causative Agent: Bluetongue virus (BTV)
• Family: Reoviridae
• Genus: Orbivirus

Transmission

• Biting midges (Culicoides spp.).

Replication Cycle

• Virus replicates in insect vector and host endothelial cells.

Pathogenesis

• Targets vascular endothelial cells, causing hemorrhage and edema.

Clinical Signs

• Fever, edema of the face and tongue.
• Coronary band lesions, lameness, cyanosis of tongue.

Control

• Vaccination with inactivated or live-attenuated vaccines.
• Vector control measures.

4. Foot-and-Mouth Disease (FMD)

• Causative Agent: Foot-and-mouth disease virus (FMDV)
• Family: Picornaviridae
• Genus: Aphthovirus

Transmission

• Direct contact with infected secretions.
• Aerosols and contaminated fomites.

Replication Cycle

• Cytoplasmic replication, lysis of host cells.

Pathogenesis

• Virus replicates in epithelium, causing vesicular lesions.

Clinical Signs

• Vesicles on mouth, feet, and udder.
• Lameness and salivation.

Control

• Routine vaccination.
• Quarantine and disinfection.

5. Orf (Contagious Ecthyma)

• Causative Agent: Orf virus
• Family: Poxviridae
• Genus: Parapoxvirus

Transmission

• Direct contact with lesions or scabs.
• Contaminated environments.

Replication Cycle

• Replicates in cytoplasm, forming intracytoplasmic inclusions.

Pathogenesis

• Virus infects epithelial cells, causing proliferative and pustular lesions.

Clinical Signs

• Crusty lesions around lips, nostrils, and udder.

Control

• Vaccination with live virus vaccine.
• Disinfection of affected areas.

6. Maedi-Visna (Ovine Progressive Pneumonia)

• Causative Agent: Maedi-visna virus
• Family: Retroviridae
• Genus: Lentivirus

Transmission

• Colostrum, milk, and respiratory secretions.

Replication Cycle

• Reverse transcription of viral RNA in host cells.

Pathogenesis

• Persistent infection causing chronic inflammation in lungs and nervous system.

Clinical Signs

• Chronic respiratory distress, wasting.
• Neurological signs.

Control

• No vaccine; manage by culling infected animals.
• Regular serological testing.

7. Caprine Arthritis-Encephalitis (CAE)

• Causative Agent: Caprine arthritis-encephalitis virus (CAEV)
• Family: Retroviridae
• Genus: Lentivirus

Transmission

• Colostrum, milk, and contact with infected fluids.

Replication Cycle

• Reverse transcription and integration into host DNA.

Pathogenesis

• Chronic inflammation in joints and nervous tissues.

Clinical Signs

• Arthritis in adults, encephalitis in kids.

Control

• Test-and-cull programs.
• Feed heat-treated colostrum and pasteurized milk.

General Prevention and Control Strategies

1. Vaccination:
   • Administer vaccines specific to the virus.
2. Biosecurity:
   • Isolate new or sick animals.
   • Disinfect equipment and facilities.
3. Quarantine:
   • Restrict animal movements during outbreaks.
4. Vector Control:
   • Manage biting insects and ticks.
5. Education:
   • Train farmers in early detection and reporting.

A combined approach focusing on vaccination, surveillance, and good management practices is key to controlling viral diseases in sheep and goats.