Kemin Industries

Yee Wong

A. Severity of the ASF disease and economic impact

African swine fever (ASF) is a hemorrhagic disease affecting all ages of domestic and wild pigs, with very high mortality during infection with virulent strains, caused by a double-stranded DNA virus. Since the outbreak reported in China in August 2018, ASF has spread rapidly to 14 Asian countries including Indonesia, Vietnam, Cambodia, Mongolia and Laos. Infected products have also been found in South Korea, Japan, Taiwan and Australia. Approximately more than 120 million pigs from these countries have died due to ASF. A study done by Asian Development Bank estimated that the ASF would cost Asia between US$55 billion to US$130 billion. Major pork producers from Asia suffered severe losses and the burden is affecting many smallholder farmers, exacerbating poverty and food insecurity in the region. ASF has escalated the prices of pork and other food supplies, and negatively impacting human health, environment and trade.

The disease can easily be transmitted by many vectors such as mosquitoes, ticks, or other arthropods. Recent studies have shown that contaminated feeds and drinking water can be a potential route for ASF virus (ASFV) transmission to domestic pigs through the consumption of contaminated feed and liquid.

ASFV replicates in mononuclear phagocytic cells and reticuloendothelial cells. This highly pathogenic disease causes symptoms such as sustained high fever, reduced feed intake to anorexia, vomiting, watery to bloody diarrhea, conjunctivitis, respiratory distress, reddened skin, cyanosis, severe depression, huddling, and incoordination. The domestic pigs and wild boars mostly develop severe clinical manifestations after virus invasion and present a mortality rate up to 100%.

The mode of action of how the ASFV induces these clinical and pathological symptoms remains to be fully elucidated. Early studies focusing on hemorrhagic lesions, the major acute pathological characteristic correlated these observations with virus replication, disseminated intravascular coagulation, and massive destruction of macrophages. Currently it is generally accepted that secretion of cytokines by the infected monocyte-macrophage system that is considered as the major target of ASFV and secondarily activated lymphocytes is strongly applied in the biological processes. Research has also shown that ASFV infection significantly altered host gene profiles and that can interfere with the host immune response leading to excessive production of proinflammatory cytokines, which is a major primary causative factor in ASF pathogenesis. The differential expression of genes also indicates that ASFV could evade both the innate and adaptive immune responses.

B. How do we contain the ASF outbreak? What are the current biosecurity measures?

ASFV consists of a complex multi-layered structure, with a lipid membrane between an inner core shell and an outer capsid. An outer lipid envelope surrounds the capsid and the virus is robust in many environments. The virus has an incubation period of approximately 4-19 days and pigs that survive mild infection can shed the virus for at least 70 days.

Biosecurity remains a critical and direct measure in ensuring disease-free farms, regions, and countries. Its adoption during an ASF outbreak not only reduces the risk of disease introduction but will also abate further financial losses. A series of management practices that prevent the spread of infectious agents between animal groups in a farm or handling practices designed to prevent the infectious agent from leaving the farm would be important measures to take. Suggested control measures include using animal identification and tracking systems, quarantine facilities, disallowing free range pig movement, banning of swill feeding, implementing ban on illegal import of pork and pork products, and introducing surveillance system in farms. Most of the time the only way to contain the virus in case of an outbreak is to either quarantine the pig population, where possible, or cull the animals.

The World Organisation for Animal Health (WOAH) also provides recommendations for disinfectant agents against ASFV such as sodium hydroxide, hypochlorite, formalin and iodine compounds. The United States Department of Agriculture (USDA) maintains a list of disinfectants approved for use against ASFV in farm applications. The Environmental Protection Agency (EPA) has approved commercial products based on chlorine, hydrogen peroxide, and potassium peroxy-monosulphate (Virkon-S). Only if a commercially approved preparation is not available it is then permitted to use sodium hypochlorite (0.3%) or citric acid (3%) with exposure times after cleaning of 15 or 30 min on non-porous and porous surfaces respectively.

Vaccination offers a highly promising strategy to prevent and control the ASF epidemic. Different approaches have been attempted by various experts such as inactivated vaccines, live attenuated vaccines and genetically-engineered vaccines (subunit vaccines, DNA vaccines, vector vaccines), but each comes with its own challenges. Since inactivated ASFV vaccines have poor immune protection and there are insufficient cell lines for efficient in vitro ASFV replication, producing an ASF vaccine with high immune-protective potential remains a limitation.Unfortunately, the inactivated vaccines have been proven to be ineffective against ASF. Most of the experiments have confirmed that inactivated vaccines led to further expansion of the epidemic and live attenuated vaccines caused a persistent infection, detoxification, and side effects in immunized pigs.

One of the live attenuated vaccines, ASFV-G-ΔI177L in Vietnam, is the first commercial ASF vaccine. Safety of attenuated vaccines, the occurrence of post-viral shedding and post-vaccination complications with a lack of biosecurity protection of immune-compromised pigs, have resulted in the limited large-scale adoption as governments remain cautious. Live attenuated vaccine development is also associated with high costs, long cycles, and instability, which restrict further development. Researchers are currently moving to genetically engineered vaccines; while most experiments were limited to immunogenicity assays, more new data is required from challenge trials to validate efficacy and safety.

Kemin’s 3D Program to help farmers – Our solutions

With the increasing prevalence of the ASF in the region, Kemin Industries acted swiftly in response to the ASF threat by introducing the 3D Approach program. This program encompasses three core dimensions, focusing on farm biosecurity, pathogen reduction in feed and enhancing gut immunity. The 3D Approach program serves as a comprehensive guide for pig producers, equipping them with the necessary tools to manage biosecurity risks and minimize the transmission of ASFV.

Within the 3D Approach program, Kemin incorporates two key solutions: Sal CURB® and Aleta®. Sal CURB® effectively deactivates ASFV in feed, while Aleta® strengthens overall pig immunity. Significant findings from our in-feed assay studies revealed the inhibitory effect of Kemin's antimicrobial formulations, Sal CURB RM E Liquid and Sal CURB K+ Liquid, on ASFV replication. These results indicate that antimicrobial compounds have the potential to serve as antiviral feed or water mitigants for ASFV infection. Notably, Kemin achieved a major milestone in 2020 by acquiring a U.S. Patent Application for an effective ASFV control solution in feed. Furthermore, a new patent has recently been filed for a formaldehyde-free formulation, Sal CURB K+ Liquid. Kemin collaborates with the National Institute of Veterinary Research (NIVR) in Vietnam and Kansas State University (KSU) in the United States to conduct research on the effectiveness in controlling ASFV in feed.

The adoption of the 3D Approach program and Kemin's solutions by key industry players has contained the spread of ASF in the region. This program has not only benefited farmers but also enabled Kemin to collaborate with local authorities and media partners to raise awareness about ASF and educate the industry on pig safeguarding measures.

Complementary to the current 3D program, Kemin's new Bio-Cide product, containing stabilized chlorine dioxide, is another valuable alternative for controlling ASFV spread. Independent studies have demonstrated that chlorine dioxide, with its broad-spectrum antibacterial activity and absence of drug resistance inhibits ASFV by blocking viral attachment and destroying viral nucleic acids and proteins.

In conclusion, the 3D Approach program, coupled with Kemin's Bio-Cide solution, offers industry players clear and effective strategies to mitigate ASF threats. This program can also be adapted to manage other infectious diseases caused by livestock pathogens, such as Porcine Epidemic Diarrhea (PED). The key principle is still to identify biosecurity threats and transmission routes and implement measures to minimize virus transmission risks. All these measures are critical to enable affected swine farms to repopulate and restore its operations to minimize further food insecurity challenges in this region.