Lesson 4: Viral diseases of pigs

1. Classical Swine Fever (CSF)

• Causative Agent: Classical Swine Fever Virus (CSFV)
• Family: Flaviviridae
• Genus: Pestivirus

Transmission

• Direct contact: Infected pigs, secretions, and excretions.
• Indirect contact: Contaminated fomites, feed, or water.
• Vertical transmission: From sow to offspring.

Replication Cycle

• Virus replicates in host cells’ cytoplasm, primarily targeting monocytes and lymphocytes.

Pathogenesis

• Immunosuppression, lymphoid necrosis, and endothelial damage leading to hemorrhages.

Clinical Signs

• Fever, anorexia, cyanosis, diarrhea, conjunctivitis, and petechial hemorrhages.
• Chronic cases: Hairy appearance, stunted growth, and secondary infections.

Control

• Vaccination with live attenuated vaccines.
• Strict biosecurity and culling of infected animals.

2. African Swine Fever (ASF)

• Causative Agent: African Swine Fever Virus (ASFV)
• Family: Asfarviridae
• Genus: Asfivirus

Transmission

• Direct contact: Infected pigs, blood, and tissues.
• Indirect contact: Contaminated feed, fomites, or ticks (Ornithodoros spp.).

Replication Cycle

• Replicates in the cytoplasm of monocytes/macrophages.

Pathogenesis

• Severe endothelial damage, apoptosis of lymphocytes, and systemic hemorrhages.

Clinical Signs

• High fever, anorexia, cyanosis, petechiae, bloody diarrhea, and sudden death.
• Chronic: Emaciation, joint swelling, and respiratory distress.

Control

• No vaccine available.
• Quarantine, biosecurity, and culling of affected animals.

3. Porcine Reproductive and Respiratory Syndrome (PRRS)

• Causative Agent: PRRS Virus (PRRSV)
• Family: Arteriviridae
• Genus: Betaarterivirus

Transmission

• Direct: Contact with infected pigs’ saliva, semen, or milk.
• Aerosol: Viral particles in respiratory secretions.

Replication Cycle

• Targets macrophages, replicating in cytoplasm.

Pathogenesis

• Immunosuppression, lymphoid depletion, and respiratory distress.

Clinical Signs

• Reproductive phase: Abortions, stillbirths, mummified fetuses.
• Respiratory phase: Fever, dyspnea, coughing, and poor growth.

Control

• Vaccination, strict biosecurity, and isolation of infected herds.

4. Swine Influenza (SI)

• Causative Agent: Swine Influenza Virus (H1N1, H3N2, etc.)
• Family: Orthomyxoviridae
• Genus: Influenzavirus A

Transmission

• Direct: Nasal secretions, aerosols from infected pigs.
• Indirect: Contaminated feed or equipment.

Replication Cycle

• Virus attaches to host respiratory epithelial cells, replicating in the nucleus.

Pathogenesis

• Epithelial damage in the respiratory tract, leading to secondary infections.

Clinical Signs

• Fever, coughing, nasal discharge, lethargy, and reduced appetite.

Control

• Vaccination, biosecurity, and proper management during outbreaks.

5. Porcine Epidemic Diarrhea (PED)

• Causative Agent: Porcine Epidemic Diarrhea Virus (PEDV)
• Family: Coronaviridae
• Genus: Alphacoronavirus

Transmission

• Fecal-oral route through contaminated feed, water, or surfaces.

Replication Cycle

• Replicates in the cytoplasm of intestinal epithelial cells.

Pathogenesis

• Villous atrophy in the small intestine, leading to diarrhea and dehydration.

Clinical Signs

• Watery diarrhea, vomiting, dehydration, and high mortality in piglets.

Control:

• Vaccination, strict hygiene, and isolation of affected herds.

6. Foot-and-Mouth Disease (FMD)

• Causative Agent: Foot-and-Mouth Disease Virus (FMDV)
• Family: Picornaviridae
• Genus: Aphthovirus

Transmission

• Aerosol: Viral particles in the air.
• Direct contact: Infected animals, secretions, and excretions.

Replication Cycle

• Virus replicates in the cytoplasm, especially in epithelial cells.

Pathogenesis

• Vesicle formation on epithelial surfaces, leading to ulceration.

Clinical Signs

• Vesicles on the snout, mouth, tongue, and hooves.
• Fever, lameness, salivation, and reduced feed intake.

Control

• Vaccination, biosecurity, and slaughter of infected animals.

7. Pseudorabies (Aujeszky’s Disease)

• Causative Agent: Pseudorabies Virus (PRV)
• Family: Herpesviridae
• Genus: Varicellovirus

Transmission

• Direct: Nasal or oral contact.
• Indirect: Contaminated equipment or feed.

Replication Cycle

• Replicates in the nucleus of epithelial and neuronal cells.

Pathogenesis

• Encephalitis, respiratory distress, and systemic infection.

Clinical Signs

• Neurological signs, respiratory symptoms, and reproductive failure.

Control

• Vaccination, biosecurity, and management of latent carriers.

General Control Measures for Viral Pig Diseases

1. Biosecurity
   • Isolate new or sick animals.
   • Disinfect equipment and vehicles.
2. Vaccination
   • Utilize vaccines specific to the prevalent viral diseases.
3. Surveillance
   • Regular health checks and monitoring of herds.
4. Hygiene
   • Maintain clean and dry housing conditions.
5. Culling
   • Immediate removal of infected or high-risk animals.

By integrating vaccination, biosecurity, and good management practices, the impact of viral diseases in pigs can be minimized.