Comprehensive Review on Key Points for African Swine Fever Prevention and Control During the Rainy Season

Laizhi^1,2, Liujunwei², Gaojunfeng¹, Panjinhua², Majingjing^1，2, Hanxiangmi¹

1、Shanghai Chuanghong  Bio-tech Ltd Co., 2、Lookup (suzhou) Bio-Engineering Ltd Co.,

 

Introduction

African Swine Fever (ASF) is a highly contagious viral disease affecting pigs, with significant economic impacts on the swine industry. The rainy season poses additional challenges for ASF prevention and control due to increased environmental risks and the potential for virus spread. This review outlines the key strategies for ASF prevention and control during the rainy season, focusing on biosafety measures, early detection, and precise elimination techniques.

 

Evolution of African Swine Fever Virus in China

Since the first report of African swine fever virus in China in August 2018, by 2023, African swine fever had evolved into multiple strains, including the classical highly virulent strain of genotype II, the classical strain of genotype I, the attenuated strain of genotype II, the gene-deleted strain, and the recombinant strain. These variants present unique challenges:

-Gene-Deleted/Recombinant Strains: Large contamination areas, asymptomatic infections, limited airborne transmission, intermittent viral shedding, long incubation periods, and increased difficulty in precise elimination.

-Type I and II Strains: Classical and emerging strains that complicate detection and control efforts.

 

Characteristics of ASF Transmission Risks During the Rainy Season

The rainy season exacerbates several risk factors for ASF transmission:

-Environmental Risks: Flooding, landslides, and waterlogging reduce the efficiency of disinfection.

-Operational Challenges: Difficulty in controlling rain gear for personnel, low efficiency of vehicle, materials disinfection, and increased risks during pig sales and transfers.

-Biological Vectors: Increased populations of mosquitoes, flies, mouse, and other insects that can carry the virus.

-Health Risks: High humidity in pig pens leads to decreased immunity and sub-health in pigs, while feed mold contamination further compromises pig health.

 

Biosafety Upgrades for Rainy Season

Infrastructure Improvements:

- Modify pig pathways to prevent water backflow.

- Frequently change disinfection basins and preferably change shoes.

- Disinfect areas after rain stops and build shelters over pig loading areas.

 

Management Strategies:

- Monitor weather forecasts and organize flood prevention teams.

- Check water sources and electrical circuits to prevent fires.

- Suspend vacations to ensure sufficient manpower and reduce personnel movement during typhoon warnings.

 

Early Detection: Frontline Whistleblowers

Early detection is crucial for controlling ASF. Training frontline staff as whistleblowers can enhance early identification of ASF symptoms:

- Clinical Symptoms:

  -Boars: Refusal to eat or eat slowly, vomiting, death, bloody stool, bloody urine (hematuria), prolonged bleeding after needle withdrawal.

  -Sows: Refusal to eat or eat slowly, vomiting, death, abortion, red ears, bloody stool, bloody urine, skin bleeding, skin necrosis plaques, black blood spots, prolonged bleeding after needle withdrawal.

   -Farrowing Pigs: Diarrhea, swollen eyes, stillbirths, abortions, mummified fetuses.

-Nursery Pigs: Refusal to eat, elevated temperature, red skin, skin necrosis plaques, red ears, bloody stool, bloody urine, huddling, diarrhea, death.

  -Fatting Pigs: Refusal to eat, vomiting, bloody stool, bloody urine, red ears, skin bleeding, skin necrosis plaques, reddening, whitening, and yellowing of the skins observed in one pig pens,  prolonged bleeding after needle withdrawal.

 

Upgrading Detection Methods

Laboratory Importance:

-Timeliness: Results within 4 hours after sampling.

-Early Warning: Testers also act as whistleblowers.

 

Laboratory Detection Upgrade Points:

- Building the Diagnosis to Doors labs: This laboratory is located near the pig farm and monitors whether personnel, vehicles, supplies, feed, and pigs entering the farm carry the African swine fever virus using PCR technology.

-Sampling Plan Upgrade for Rainy Season:

  - High-risk areas: Focus on environmental and personnel samples, with abnormal pigs as supplementary.

  - High-risk pig groups: Use three-swab method sows (The Three Swab Method: one oral-nasal swab, one tail-root blood swab, and one environmental swab from the pig pen railing), cotton rope for nursery or fattening pigs, and internal environmental samples for abnormal pigs.

  - Sampling frequency:

-Highly risk pigs: environmental (dry areas), oral/nasal, saliva swabs, blood swabs are collected once a day for three consecutive days.

-Medium risk pigs: environmental (dry areas), oral/nasal, saliva swabs are collected once a day for three consecutive days. Blood swabs are only collected from abnormal pigs.

-Low risk pigs: environmental (dry areas), oral/nasal, saliva swabs are collected once every 7 days. Blood swabs are only collected from abnormal pigs.

Detection System Upgrade:

- PCR Diagnostic Sensitivity Upgrade: Primer design must match ASFV virus variations, prepare dual and triple PCR kits, upgrade PCR detection equipment.

-Antigen Rapid Test Kit: It is used for oral/nasal, saliva, blood swabs collected from abnormal pigs, Results are available in 10 minutes.

- Antibody Detection Upgrade: Use P54/P72, P30, and CD2v antibody ELISA detection kits.

- Antibody Rapid Test Kit: It is used for blood swabs collected from abnormal pigs, and results are available in 10 minutes.

 

Precise Elimination and Purification During the Rainy Season

Culling System Upgrade:

- Ensure drainage in pig pathways and follow terrain for pig movement.

- Disinfect and incinerate protective clothing, disposable gloves, and colored cloth.

- Change shoes, disposable gloves, and protective clothing before entering pig pens.

- Increase disinfectant concentration and control humidity in pig pens.

- Prefer high-temperature treatment or soaking for material entry and control flies, mosquitoes, and rats.

 

Case Studies

Case 1: Northwest, Gansu Farm

- Pre-Rain: Check drainage, disinfect production, living, and external areas, bulk purchase and disinfect materials, check electrical safety, empty sewage pools, form flood prevention teams.

- During Rain: Flood prevention teams patrol, avoid pig transfers and sales.

-Post-Rain: Sample rainwater-rich areas, add anti-stress additives to pigs, conduct biosafety sampling, repair leaks.

 

Case 2: Southern, Guangdong Farm

- Pre-Rain: Check drainage, disinfect production, living, and external areas, bulk purchase and disinfect materials, check electrical safety, empty sewage pools, form flood prevention teams, trim tall shrubs, eliminate scavengers.

-During Rain: Flood prevention teams patrol, avoid pig transfers and sales.

-Post-Rain: Sample rainwater-rich areas, add anti-stress drugs to pigs, conduct biosafety sampling, repair leaks.

 

Conclusion

Effective ASF prevention and control during the rainy season require a comprehensive approach that includes infrastructure improvements, management strategies, early detection, and precise elimination techniques. Training frontline staff as whistleblowers and upgrading laboratory detection methods are crucial for early identification and control of ASF. By implementing these strategies, the swine industry can mitigate the risks associated with ASF during the rainy season and protect pig health and productivity.