What can we learn from the five-year African swine fever epidemic in Asia?

Characterization of biosecurity practices and viral infections on pig farms in Hong Kong

The objectives of this study were to characterize the biosecurity practices implemented on pig farms in Hong Kong and determine the between-farm prevalence of economically important viral pathogens. All active pig farms in Hong Kong (n = 40) were invited to participate in an interview-based survey using a Biocheck-UGent™ questionnaire to evaluate their biosecurity practices. Pen-level oral fluid samples were collected by cotton ropes to detect six target viral pathogens using RT-PCR: porcine reproductive and respiratory virus (PRRSV), porcine circovirus type-2 (PCV-2), swine influenza virus (SIV), porcine delta-coronavirus (PDCoV), porcine epidemic diarrhea virus (PEDV), and transmissible gastroenteritis virus (TGEV). Eighteen farms (45 %) accepted our invitation and participated in this study. Biosecurity practices were found to be inadequate in many areas, with an average overall score of 50.1 ± 9.4 (mean ± SD). The study farms scored higher for external biosecurity (56.4 ± 8.6) than internal biosecurity practices (43.9 ± 12.1). Among external biosecurity subcategories, breeding pig and semen purchase scored highest (93.2), while visitors and farmworkers scored lowest (23.5). In internal biosecurity, the disease management subcategory received the highest score (66.7). Only two external biosecurity subcategories, breeding pig and semen purchase (93.2), and farm location (70) exceeded the global average scores. Key deficiencies were identified in biosecurity protocols for visitors and workers, hygiene standards for feed, water, and equipment supplies, and measures to prevent disease transmission between compartments (farrowing, nursery, and finishing units). Over 90 % of participating farms implemented vaccination programs for PRRSV, PCV-2, porcine parvovirus (PPV), pseudorabies virus (PRV), and classical swine fever virus (CSFV) while no farms vaccinated against SIV, and vaccination for swine coronaviruses was sporadic. All target viruses except TGEV were detected at the farm level. The between-farm prevalences among the 18 study farms were PRRSV-2 (94.4 %), PRRSV-1 (38.9 %), PCV-2 (83.3 %), SIV (55.6 %), PDCoV (16.7 %), and PEDV (5.6 %). We provided comprehensive baseline information on the biosecurity practices of pig farms for the first time in Hong Kong. We identified critical areas of biosecurity for improvement and offered tailored recommendations to help the producers implement more effective prevention and control strategies for infectious diseases within and between farms.

Reproductive Failure in Smallholder Pig Farms in East and Southeast Asia: A Systematic Review

Reproductive failure has significant socioeconomic impacts on smallholder pig farms. This systematic review was conducted to compile the types of reproductive failures and their underlying causes reported in smallholder pig farms from East and Southeast Asia and to identify relevant knowledge gaps. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 26 peer-reviewed studies met the eligibility criteria and were included in our synthesis. These studies were conducted in 11 countries, with Vietnam, China, and Thailand representing the highest share (53.8%). Only six studies (23%) investigated reproductive failure as their primary objective. Stillbirth, mummification, late-term abortion, and weak-born piglets were the predominant reproductive failures reported from smallholder pig farms across the region. The most frequently cited viral pathogens associated with these failures were porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV-2). Common non-infectious risk factors included extreme climate conditions (e.g., heat stress), poor diet and housing, and suboptimal boar management. Our synthesis highlighted a dearth of research focused on reproductive failure in smallholder pig farms in the region and emphasised the need for more targeted studies to clarify the biological, environmental, and managerial risk factors contributing to reproductive failure. This will facilitate the development of targeted prevention and control measures that account for the unique farming conditions and challenges smallholder farms face in East and Southeast Asia.

Genetic Profiles of Ten African Swine Fever Virus Strains from Outbreaks in Select Provinces of Luzon, Visayas, and Mindanao, Philippines, Between 2021 and 2023

An African Swine Fever (ASF) outbreak was first recorded in the Philippines in July 2019. Since then, the disease has spread across provinces in Luzon, Visayas, and Mindanao, causing severe economic consequences for the country's swine industry. Here, we report the genome sequencing of ASF virus strains from outbreaks in several provinces of the Philippines between 2021 and 2023, using a long-read tiled amplicon sequencing approach. The coding-complete genomes generated ranged from 187,609 to 189,540 bp in length, with GC contents of 38.4% to 38.5%. Notably, a strain from the Bataan province had a 1.9 kb deletion at the 5'-end, affecting several coding regions. The strains were characterized using 13 genes and regions; namely the B646L gene, the CD2v serogroup, the central variable region (CVR) of the B602L gene, the intergenic region (IGR) between the I73R and I329L genes, the IGR between A179L and A137R, O174L, K145R, Bt/Sj, J268L, and ECO2, the multigene family (MGF) 505-5R, and the MGF 505-9R and 10R regions. The ASFV strains were mostly related to Asian and European p72 genotype II strains. Genetic profiling provides valuable information on the diversity of local strains of ASFV in the Philippines, which are useful for epidemiology, diagnostics, and vaccine development.

African swine fever incursion risks in Latin America and the Caribbean: informal and legal import pathways

African swine fever (ASF) is a devastating hemorrhagic disease of swine with high mortality rates and severe socioeconomic impacts on affected pig industries. In 2021, ASF was reported in the Americas for the first time in 40 years, prompting risk assessments for its introduction and spread. This study evaluates ASF incursion risk across 40 territories in the Caribbean, Central America, North America, and northern South America. A structured, multi-step assessment synthesized peer-reviewed literature, government reports, gray literature, and epidemiological databases to classify two primary ASF incursion pathways: informal imports (e.g., traveler-carried pork, illegal migration, unregulated waste disposal) and legal imports (e.g., trade in live swine and pork products). Territories were categorized as "Probable," "Unlikely," or "Unknown," with certainty levels (Low, Medium, High) based on data robustness. Results indicate ASF incursion is "Probable" (Medium certainty) via informal or formal imports in the Bahamas, British Virgin Islands, Colombia, Cuba, Jamaica, Mexico, Panama, Puerto Rico, Venezuela, Turks and Caicos, and the U.S. Virgin Islands. In contrast, Barbados, Bermuda, Costa Rica, El Salvador, and Guyana were classified as "Unlikely" (Medium certainty) to experience an ASF outbreak under current conditions. Due to insufficient data, 24 territories were categorized as "Unknown" (Low certainty), highlighting critical knowledge gaps. These findings emphasize the need for enhanced surveillance, systematic data-sharing, and regional collaboration to improve risk assessments and implement effective ASF prevention measures in the Americas.

The effect of swine insurance participation on swine production efficiency: Evidence from China

How does swine insurance affect the swine production efficiency in China? We focus on micro-survey data from 582 swine farmers in Liaoning Province, and uses the propensity score matching method (PSM) and mediated effects model for the empirical examination. The results indicate that swine insurance positively impacts production efficiency, compared to uninsured farmers, those who participate in swine insurance exhibit a 4.7% improvement in production efficiency. Additionally, the estimations from the mediated effects models indicate that swine insurance significantly enhances swine production efficiency by influencing risk appetite, production decision and technology adoption. Furthermore, the heterogeneity analysis revealed that the positive effect of swine insurance on production efficiency becomes more pronounced as the scale of farmers' swine production expands. Apart from this, the correlation between swine insurance coverage level and production efficiency reveals a significant U-shaped curve. These findings provide valuable insights for improving the swine insurance system and fostering the growth of the swine industry.

First Outbreak of African Swine Fever in Wild Boar in Nepal

This case report documents the first confirmed outbreak of African swine fever (ASF) in a wild boar (Sus scrofa) in Nepal. The case was identified in a wild boar carcass found in Shuklaphanta National Park in February 2023. Post-mortem findings, including splenomegaly, haemorrhagic lymph nodes and congested organs, were suggestive of ASF, which was confirmed by real-time PCR. Epidemiological evidence indicates potential transmission from nearby ASF-infected domestic pigs. This case underscores the critical need for rigorous biosecurity protocols, comprehensive surveillance and targeted wildlife management strategies to prevent further transmission between domestic pig and wild boar populations.

A Novel and Rapid Selective Viral Genome Amplification and Sequencing Method for African Swine Fever Virus

African swine fever virus (ASFV) is the etiological agent of African swine fever, a highly contagious hemorrhagic disease affecting both wild boars and domestic pigs with lethality rates up to 100%. Until now, the most effective measure to prevent an outbreak of ASFV was early detection. In this situation, whole genome sequencing (WGS) allows the gathering of detailed information about the identity and epidemiology of the virus. However, due to the large genome size and complex genome ends, WGS is challenging. Current WGS workflows require either elaborate enrichment methods or are based on tiled PCR approaches, which are susceptible to genetic differences between ASFV strains. To overcome this, we developed a novel approach for WGS of ASFV, using the Phi29 DNA polymerase-based multiple displacement amplification in combination with only seven primers. Furthermore, we applied an alkaline-based DNA denaturation step to significantly increase the number of viral reads, which resolves the near-full genome of ASFV. This novel isothermal WGS approach can be used in authorized laboratories for the genomic epidemiological analysis of ASFV outbreaks caused by different genotypes.

Genotype II Live-Attenuated ASFV Vaccine Strains Unable to Completely Protect Pigs against the Emerging Recombinant ASFV Genotype I/II Strain in Vietnam

Background: African swine fever virus (ASFV) continues to spread globally, causing severe economic losses to pig farmers. Vietnam licensed two live attenuated vaccines based on the ASFV strains ASFV-G-ΔI177L and ASFV-G-ΔMGF to control the ongoing ASF outbreaks. In 2023, newly emerging highly virulent recombinant ASF viruses (rASFV I/II) containing genetic elements from both p72 genotype I and II ASF viruses were reported from Northern Vietnam. Objective: This study evaluated whether the two vaccine strains were able to protect the pigs against the emerging rASFV I/II strain VNUA/rASFV/TN1/23. Results: Pigs vaccinated with ASFV-G-ΔMGF or ASFV-G-ΔI177L, when challenged with rASFV I/II, succumbed to the infection, or developed signs of chronic ASF. Conclusions: The findings from this study show that both vaccine strains that are licensed and used in Vietnam are unlikely to protect pigs from the emerging highly virulent rASFV I/II. This complicates the ongoing efforts to control ASF in Asia and globally and emphasizes the urgent need for a novel vaccine that can effectively protect pigs from the rASFV I/II.

Multiplex PCR Approach for Rapid African Swine Fever Virus Genotyping

African swine fever virus (ASFV) has been spreading through Europe, Asia, and the Caribbean after its introduction in Georgia in 2007 and, due to its particularly high mortality rate, poses a continuous threat to the pig industry. The golden standard to trace back the ASFV is whole genome sequencing, but it is a cost and time-intensive methodology. A more efficient way of tracing the virus is to amplify only specific genomic regions relevant for genotyping. This is mainly accomplished by amplifying single amplicons by PCR followed by Sanger sequencing. To reduce costs and processivity time, we evaluated a multiplex PCR based on the four primer sets routinely used for ASFV genotyping (B646L, E183L, B602L, and intergenic I73R-I329L), which was followed by Nanopore ligation-based amplicon sequencing. We show that with this protocol, we can genotype ASFV DNA originating from different biological matrices and correctly classify multiple genotypes and strains using a single PCR reaction. Further optimization of this method can be accomplished by adding or swapping the primer sets used for amplification based on the needs of a specific country or region, making it a versatile tool that can speed up the processing time and lower the costs of genotyping during ASFV outbreaks.

The Comparative Full-Length Genome Characterization of African Swine Fever Virus Detected in Thailand

African swine fever virus (ASFV) has been responsible for the globally devastating epidemics in wild and domesticated pigs. Of the 24 identified ASFV genotypes, genotype II is the primary cause for the pandemic occurring in Europe and Asia since its emergence in Georgia in 2007. The current study aimed to characterize the full-length genomic pattern of the ASFV strain from Thailand, TH1_22/CR (Accession No. PP915735), which was then compared with genomic diversity across other Asian isolates using Georgia 2007/1 (Accession No. FR682468) as the reference. Viral DNA was isolated from the pig spleen sample following library preparation and paired-end sequencing using the MiSeq Illumina platform. The sequenced TH1_22/CR isolate spanned 189,395 nucleotides encoding 193 open reading frames (ORFs), exhibiting maximum nucleotide similarity (99.99%) with Georgian (Georgia 2007/1) and Chinese (Wuhan 2019-1 and China HLJ) isolates. Based on phylogenetic analysis, the TH1_22/CR isolate (Accession No. PP915735) was characterized as genotype II, serogroup 8, and IGR-II due to the presence of three tandem repeat sequences (TRSs). Genetic variations including SNPs and single and polynucleotide indels were identified in TH1_22/CR in agreement with other Asian isolates. For comprehensive analysis, the genome was divided into four regions (I-IV) based on gene location. Overall, the TH1_22/CR isolate demonstrated eight SNPs and indels in its genome. Two unique SNPs were reported in the coding regions of the TH1_22/CR isolate, out of which, a C-591-T substitution was seen in MGF 360-4L and a C-297-T was found in A238L, and four unique SNPs were reported in non-coding regions (NCRs). Furthermore, a 29 bp deletion was observed in the IGR between MGF 110-13La and MGF 110-13Lb, as well as 52 bp deletion in the ASFV G ACD 00350 gene. This comparative analysis establishes the foundational information for future studies on the diversity and phylogeography of this regionally significant genetic sub-group of ASFV.

Evaluation of Selective Culling as a Containment Strategy for African Swine Fever at a Vietnamese Sow Farm

Selective culling, also known as the "tooth extraction approach", is a strategy for controlling African swine fever (ASF) by removing only sick and suspect animals instead of the entire herd in Vietnam. This method prioritizes preserving healthy animals, particularly valuable breeding pigs. Despite its implementation in various forms, no standardized protocol based on scientific principles has been established. Farms typically adapt this strategy based on their understanding, which can vary significantly. In implementing of selective culling that is not based on scientific principles, there is a significant risk of spreading the disease. The aim of this study is to evaluate the consequences of selective culling as currently implemented in Vietnam. Our analysis on a large sow farm revealed that current practices rely heavily on clinical observations without laboratory confirmations. This approach allows ASF-infected animals to remain on the farm longer, potentially exacerbating the spread of the virus. Thus, selective culling poses a substantial risk by potentially exacerbating the spread of disease. Our findings emphasize that early diagnosis of ASF and systematic removal of infected pigs are critical components for the effective implementation of selective culling strategies and that a high level of fragmentation to minimize contact between animals plays a key role. The optimal approach is to test conspicuous animals and separate them. Under no circumstances should suspect animals be left in the herd for several days before they become severely ill and succumb to the disease.

- Invited Review - Current status, challenges and prospects for pig production in Asia

Asia is not only the primary region for global pig production but also the largest consumer of pork worldwide. Although the pig production in Asia has made great progress in the past, it still is confronted with numerous challenges. These challenges include: inadequate land and feed resources, a substantial number of small-scale pig farms, escalating pressure to ensure environmental conservation, control of devastating infectious diseases, as well as coping with high temperatures and high humidity. To solve these problems, important investments of human and financial capital are required to promote large-scale production systems, exploit alternative feed resources, implement precision feeding, and focus on preventive medicine and vaccines as alternatives to antibiotics, improve pig breeding, and increase manure recycling. Implementation of these techniques and management practices will facilitate development of more environmentally-friendly and economically sustainable pig production systems in Asia, ultimately providing consumers with healthy pork products around the world.

Disease Course of Korean African Swine Fever Virus in Domestic Pigs Exposed Intraorally, Intranasally, Intramuscularly, and by Direct Contact with Infected Pigs

African swine fever (ASF) is a fatal contagious disease affecting swine. The first Korean ASF virus (ASFV) isolate (Korea/Pig/Paju1/2019) was used to compare the disease course of ASFV in pigs inoculated via the four routes. In the challenge experiment, domestic pigs were infected via the intraoral (IO) and intranasal (IN) routes with a 106 50% hemadsorbing dose (HAD50) and an intramuscular (IM) injection of 103 HAD50. In the direct contact (DC) group, five naïve pigs were brought into direct contact with two IM-ASFV-infected pigs. IO-, IN-, and IM-inoculated pigs showed similar disease courses, whereas DC pigs had comparable ASF syndrome after a 7-day latent period. The disease course in the DC route, one of the most common routes of infection, was not significantly different from that in the IO and IN routes. IM and DC groups differed in terms of the severity of fever and hemorrhagic lesions in the lymph nodes and spleen, indicating that the IM route, suitable for early vaccine development trials, is not appropriate for studying the ASFV infection mechanism, including early stage of infection, and IO and IN challenges with a designated dose can be alternatives in trials for assessing ASFV pathogenicity and vaccine efficacy investigations.