Addressing ASF and strategies to mitigate its impact

The ASF virus is unique due to its large and highly complex DNA structure. (Photo credit US Dept of Homeland Security)

Even as pig industries around the region recover, the threat of ASF looms, and producers continue to look for ways to address it and minimize the impact on operations. Toward this end, APC has been organizing the ‘ASF Expert Series’ webinar to share the global status of ASF and explore some of the strategies to mitigate its impact, writes ISA Q TAN.

In the series’ second installment held in August, Sandra Blome, Head of the German National Reference Laboratories for African and Classical swine fever, updated participants on the properties of ASF and the current global situation. She also discussed the virus transmission pathways through different matrices.

ASF characteristics

Sandra Blome

“The ASF virus (ASFv) is unique due to its large and complex DNA structure, and most of its functionalities are still unknown,” Dr Blome said.

She explained that the virus replicates in macrophages, thus it can avoid the immune system. Being an arthropod-borne virus, infectivity is bound to blood transmission. Without ticks, contagiousness is considered moderate; however, the infected animals usually die.

After four days of infection, the most common symptoms are high fever, reluctance to move, conjunctivitis, vomiting, diarrhea, somnolence, disorientation, seizures, and hemorrhages, which usually lead to death.

Under favorable conditions, moist and cool, the ASFv can survive up to 10 days in feces. It can also survive 70 days in blood at room temperature, 15 weeks in cooled ham, and years in frozen carcasses and pork. The virus is stable at a pH range of 4-11.

Commercial disinfectants, organic acids, hypochlorite, iodine, quaternary ammonium compounds, and lime slurry are considered effective against the enveloped ASFv. Heat treatment at 70℃ for 20 minutes or at 60℃ for 30 minutes inactivates the virus. The combined application of drying, heating, and lowering of pH is an effective control measure.

While pig industries in the region are now recovering, the threat of ASF still looms.

Transmission pathways

Despite some confusion, it is important to note that ASF has no zoonotic potential. Its natural hosts are domestic pigs and Eurasian wild boars. Other hosts, such as African wild suids and soft ticks, are also causes of concern.

The transmission pathway in the ASFv’s sylvatic cycle is maintained by a cycle of infection involving warthogs and the soft tick vector. Ticks become infected by feeding on young warthogs, which develop transient viremia.

Once introduced into the domestic pig population, direct contacts and indirect contacts (swill feeding, feed matrices, bedding materials) are the main risk factors and poor biosecurity favor transmission.

Oral infection through feed is not easy but possible at a high virus concentration. Freshly cut grass and feed grains could be contaminated with slurry from affected holdings and wild boar carcass in the area.

Dietary strategies

Javier Polo, APC’s Senior Vice-President for Global R&D, discussed the biosafety of spray-dried plasma (SDP) and dietary strategies to maximize the efficacy of pig production.

Javier Polo

Dr Polo explained that the spray-dried plasma produced by APC is functional, safe, and effective for use in animal feeds due to its stringent blood collection, testing, and multiple inactivation processes.

Spray-drying to achieve a minimum of 80℃ throughout the substance is a recognized inactivation step for viruses, including ASFv. This is a validated method to eliminate certain animal health risks in meat and milk for human consumption.

Post-drying heat treatment and an extended holding period at a minimum of 20℃ for 14 days has been shown to inactivate several viruses, including ASFv. These combined multiple processing steps is the most effective strategy to reduce and eliminate potential pathogens, compared to the sum of individual steps.

To further enhance the safety of SDP, the liquid plasma undergoes UV-C radiation before spray drying. It is a redundant safety step but is worth taking as UV-C light targets nucleic acids and inactivates multiple classifications of bacteria and enveloped or non-enveloped viruses.

Studies have shown that UV-C treatment of liquid plasma resulted in a log10 reduction of PRRSV (>5.2), PEDV (>4.0), ASFV (>4.5), and the most heat-stable virus, PPV (>4.0). In theory, a combined treatment of spray-drying, UV-C, and storage at 20℃ for 14 days could achieve >10 log10 virus reduction.

For related stories, please see:
Spray-dried plasma boosts gut health, slows down ASFv infections
Research shows feed a low risk for transmitting ASFv
Gut health and immunity play a role in ASF prevention
Ensuring ASF-free spray-dried plasma

Editor, Asian Pork Magazine, Manila, Philippines. Isa is the in-house expert on African swine fever, as her deep knowledge on the subject is imbued in articles such as, ‘Strategic testing and extraction help farms survive ASF’.