Minimizing ASF spread via proper disinfection

Without an ASF vaccine, the only way to fight the virus is to practice stringent biosecurity in farms. Disinfection plays a key role. MELIYANA writes how disinfectants, and their proper use, can help in preventing ASF spread in the future.

Biosecurity is critical because it is an effective weapon against ASF and other infectious diseases.

Fernando Robert Yu

Fernando Robert Yu, Animal Health Product Manager East and Southeast Asia of Evans Vanodine International plc told Asian Agribiz that biosecurity is an integrated approach with three principles: segregation, cleaning, and disinfection.

Segregation creates and maintain barriers to limit opportunities for infected animals and contaminated materials to enter an uninfected site. Cleaning removes interfering organic material that affects the efficacy of disinfectants. Finally, disinfection should kill and inactivate pathogens like the ASF virus on contaminated surfaces.

Not so simple

Disinfectants are chemical agents designed to inactivate or destroy microorganisms on inert surfaces.

Dr Yu said there are several families of disinfectants, each with a mode of action versus microorganisms. The most commonly used are halogens (eg iodine, chlorine), aldehydes (eg formaldehyde, glutaraldehyde), peroxygens (eg hydrogen peroxide, peracetic acid), and quaternary ammonium compounds (eg benzalkonium chloride).

But simply using these agents guarantees failure. Unlike in household environments, “there are several interfering factors present in a farm that will neutralize these chemicals.”

He explained that a disinfectant must be properly formulated for farm use by adding other ingredients that can help overcome these interfering factors.

An example of a well-designed vehicle disinfection shed. Photo courtesy of Evans Vanodine International plc.
A wrong way to disinfect a vehicle. Photo courtesy of Evans Vanodine International plc.

International approval

Dr Yu remarked that when it comes to a disease like ASF, the use of a “generic” disinfectant formula is not enough to contain the virus. A disinfectant’s efficacy can only be assured when it has been tested in at least one of the international reference labs for ASF. These include the OVI in South Africa, CIS-INIA in Spain, and the Pirbright Institute in the UK.

“The test protocols in these labs attempt to replicate the interfering factors found on a farm. Under such conditions, the disinfectant must achieve at least a log 4 (99.99%) kill to pass. This gives it international recognition as being able to kill ASF in farm conditions,” he explained.

Characteristics of disinfectant

While disinfectants may seem a silver bullet against ASF and other swine diseases, there are also risks and circumstances where their use is not optimized.

Dr Yu said disinfectants are chemicals designed to kill organisms. Chemicals that are safer for humans and animals (such as quaternary ammonium compounds) tend to have a narrower spectrum of kill. Those with a stronger chemical activity kill a wider range of pathogens but are either corrosive (like peroxygens) or harmful if exposure is too much (like formaldehyde).

Betty Yuriko

“If we use disinfectants properly, we can protect the herd from ASF and other pathogens, achieve optimal performance, and spare customers from economic losses,” Betty Yuriko, Senior Technical Manager of Zoetis Animal Health Indonesia told Asian Agribiz.

Correct use is critical

But why do some farmers continue to have problems despite the use of disinfectants? Waranee Prakatthagomol, Senior Technical Advisor of Better Pharma Co Ltd revealed that correct concentration and contact time are critical for disinfectants to work.

She explained that three factors lead to disease: susceptible host (susceptible animal), pathogens, and environment. Disinfectants address only the pathogens, so if problems continue with the animal and the environment, diseases can reoccur.

Dr Betty said it is important to select the disinfectant with good efficacy and apply them correctly.

“The proper use of disinfectants requires users to wet surfaces, such as walls, floors, etc. The most common problem is that not all surfaces are ‘touched’ by disinfectants, so some areas are still contaminated,” she added.

Waranee Prakatthagomol

Dr Waranee explained that in her experience, “farmworkers think all disinfectants are the same, but this is not so. [They must] use the disinfectant with the correct concentration.”

She said the FAO and OIE-recommended contact time to kill the ASF virus with disinfectants is 30 minutes. Shorter contact time will allow “some viruses to survive and these can infect susceptible pigs.”

Disinfection methods

Among the popular ways to apply disinfectants is liquid spraying using a pressure washer and wide-angle nozzle, and dipping of footwear and tires. Foaming of nonabsorbable surfaces is also becoming more popular in order to increase contact time.

“The key is to expose entire surfaces for as long as possible so the disinfectant has time to kill the virus,” Dr Yu said, adding that “this is something some farms take for granted leading to infection breaks and failure in biosecurity.”

One of the most important risk factors identified in ASF spread is vehicles, as these often visit several farms. Simply spraying disinfectants on the outer rim of tires or the use of poorly maintained wheel disinfection baths fail in preventing infection on the farm.

Disinfectants used must be safe for humans and animals. Photo courtesy of Evans Vanodine International plc.

“Many operations in Asia have therefore invested in dedicated vehicle disinfection centers to ensure that the vehicles’ entire surfaces are properly cleaned and disinfected. This has helped in curbing the spread of ASF to these farms,” he explained.

Dr Waranee said that organic matter reduces the efficacy of disinfectants, so cleaning vehicles before disinfecting is highly recommend. Dry clean and wet clean can remove the organic matter, thus enhancing the ability of disinfectant to kill the virus.

After identifying the critical control points in the operations, devising a plan, and selecting appropriate cleaning and disinfectant to use, the final step for farms is to document everything into an auditable program to ensure compliance with the procedure.

“Disinfectant is only one piece in the jigsaw puzzle that is biosecurity. Therefore, you need to consider all biosecurity procedures, not only the disinfectant,” Dr Waranee added.

Farmers must be educated about the proper use of disinfectants to ensure successful use. Photo courtesy of Evans Vanodine International plc.