Model Answer
0 min readIntroduction
Swine Fever (SF), also known as Classical Swine Fever (CSF), is a highly contagious viral disease affecting domestic and wild pigs. Initially recognized in Spain in 1819, it remains a significant threat to the global swine industry, causing substantial economic losses due to mortality, trade restrictions, and control measures. The causative agent is the Classical Swine Fever Virus (CSFV), a single-stranded RNA virus belonging to the *Flaviviridae* family. While not a zoonotic disease (not transmissible to humans), its impact on pig farming necessitates stringent biosecurity and control protocols. The recent outbreaks in various countries highlight the need for continued vigilance and research.
Etiology
Classical Swine Fever Virus (CSFV) is the etiological agent. It is an enveloped, single-stranded RNA virus. There are several genotypes of CSFVs, classified into subtypes based on genomic analysis. These subtypes vary in virulence, influencing disease severity. The virus is resistant to many common disinfectants, contributing to its persistence in the environment. Transmission primarily occurs through direct contact with infected pigs, contaminated feed or water, or through biological vectors like ticks (though this is less common now).
Pathogenesis
Following infection, CSFVs replicate rapidly in macrophages and other cells of the monocyte-macrophage lineage. This immune cell tropism allows the virus to spread systemically. The virus initially infects the tonsils and lymphoid tissues, then disseminates via the bloodstream to the liver, kidneys, spleen, and lungs. The pathogenesis involves a complex interplay between viral replication and the host's immune response. The immune response is often inadequate, particularly in younger pigs, leading to widespread viral replication and tissue damage. The virus suppresses interferon production, further hindering the immune system's ability to control the infection.
Symptoms
Clinical signs vary depending on the virus strain, pig age, and immune status.
- Young Pigs (under 3 weeks): Often die without showing any signs.
- Older Pigs: Symptoms include:
- Fever (often sudden onset)
- Loss of appetite
- Lethargy
- Depression
- Skin erythema (redness), particularly on the ears, abdomen, and legs
- Jaundice
- Diarrhea (often bloody)
- Respiratory distress
- Neurological signs (e.g., incoordination, seizures)
The disease progresses rapidly, and mortality rates can be high, particularly in naive pig populations.
Post-Mortem (PM) Lesions
PM examination reveals characteristic lesions:
- Skin: Erythema, petechial hemorrhages (small, pinpoint hemorrhages)
- Lymphoid tissues: Enlarged, hyperemic (red and congested) spleen and lymph nodes.
- Liver: Mottled appearance (patchy yellow and dark red), hemorrhages, and necrosis.
- Kidneys: Uremic (darkened) appearance.
- Heart: Epicardial hemorrhages.
These lesions are diagnostic but can be variable depending on the stage of infection.
Diagnosis
Diagnosis relies on a combination of clinical signs, PM findings, and laboratory tests:
- Clinical suspicion: Based on signs and history.
- Virus isolation: From blood or tissue samples (gold standard but requires biosafety level 3 facilities).
- RT-PCR (Reverse Transcription Polymerase Chain Reaction): Highly sensitive and specific for detecting CSF viral RNA.
- ELISA (Enzyme-Linked Immunosorbent Assay): Detects viral antigens or antibodies.
- Immunohistochemistry: Detects viral antigens in tissue sections.
- Differential diagnosis: Rule out other diseases with similar signs, like Porcine Reproductive and Respiratory Syndrome (PRRS) and Porcine Circoviral Disease (PCV).
Control
Control measures are crucial to prevent and contain CSF outbreaks:
- Strict Biosecurity: Restricting access to farms, controlling movement of pigs and people, and implementing disinfection protocols.
- Vaccination: Live attenuated vaccines are available, providing good protection but requiring regular boosters. Vaccination is often mandated in areas with endemic disease.
- Movement Restrictions: Quarantine of infected farms and restrictions on pig movement.
- Culling: Destruction of infected and in-contact pigs is often necessary to eradicate the virus.
- Surveillance: Regular testing of pig populations to detect the virus early.
- Improved Pig Husbandry: Reducing stress and improving overall health of pigs to enhance their resilience to infection.
- National Swine Fever Eradication Program: Countries like Japan have successfully eradicated CSF through a combination of stringent control measures and surveillance.
| Method | Advantages | Disadvantages |
|---|---|---|
| Vaccination | Reduces mortality and morbidity | Requires regular boosters, potential for vaccine-induced immunity interference |
| Culling | Effective for eradication | Significant economic losses, ethical concerns |
Conclusion
Swine Fever remains a significant threat to global swine production, demanding constant vigilance and robust control strategies. Understanding the disease's etiology, pathogenesis, clinical signs, and diagnostic methods is paramount for effective prevention and management. A combination of stringent biosecurity measures, vaccination programs, and rapid response protocols is essential to minimize its impact and work towards its eventual eradication. Continued research into improved diagnostics and vaccines is also critical for long-term disease control.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.