The primary purpose of this research study was to determine if liquid microbicides commonly used in swine production facilities demonstrated virucidal efficacy against African swine fever virus (ASFV). In collaboration with National Pork Board (NPB) stakeholders, a list of common disinfectants was identified, and specific commercial off-the-shelf products were prioritized for testing. Commercially manufactured disinfectants evaluated in this study represented a wide range of chemically active ingredients and included VirkonTM
S (potassium peroxymonosulfate), Virocid® (quaternary ammonium/ glutaraldehyde), Synergize® (quaternary ammonium/glutaraldehyde), Tek-Trol® (phenol), and Intervention® (hydrogen peroxide). Additionally, reagent-grade solutions of both citric and acetic acid (organic acids) were tested.
Using a standardized quantitative carrier test method published by the International Organization for Economic Cooperation and Development (OECD, 2013), the reduction in infectious ASFV was determined after exposure to each test chemical and acid solution at the concentration and contact time specified on the product labels for use against viruses of veterinary importance in farm settings. Efficacy tests were conducted on non-porous stainless-steel discs and porous unpainted concrete test coupons using methods published by Gabbert, et al. (2020).
The U.S. Environmental Protection Agency (EPA) Antimicrobials Division requires demonstration of a minimum 3 log10 (99.9%) reduction in infectious viral titer to designate a disinfectant as efficacious for the purposes of product registration. Using this cutoff as our standard, and under the conditions tested, we determined that on non-porous stainless steel, VirkonTMS (1%), Virocid® (1:256), acetic acid (3%), and citric acid (3%) solutions met the minimum 3 log10 performance standard when ASFV was dried in a standardized soil load. Similar tests conducted on porous concrete demonstrated that Virocid® and VirkonTMS were capable of inactivating >3 log10 ASFV on that surface. These results suggest that some chemical disinfectants may require longer contact times or higher concentrations when used for the purpose of ASFV inactivation on porous concrete, and that acid solutions, while effective on non-porous stainless steel, have reduced efficacy when applied to concrete.
Of the 7 disinfectants evaluated in this study, only VirkonTMS and citric acid are registered by the EPA for use against ASFV and were included as internal benchmarks to validate the test method. Thus, completion of these efficacy tests resulted in the identification of two additional liquid disinfectants (Virocid® and acetic acid) which demonstrated virucidal efficacy by meeting the minimum 3 log10 reduction for ASFV inactivation.
Post-disinfection, sample eluates were analyzed by real-time polymerase chain reaction (RT-PCR) to determine whether exposure to the test chemicals resulted in an appreciable reduction in the ASFV DNA signal. In general, minimal changes in cycle threshold (Ct) values were observed after the 10-minute contact time. RT-PCR can detect very small segments of viral DNA, so while degradation of the ASFV nucleic acid genome may occur after contact with chemical disinfectants, it is insufficient to destroy DNA beyond the assay limit of detection.
In this report we provide efficacy data obtained via standardized test methods to allow industry stakeholders to proactively choose disinfectants that are effective against ASFV. Chemicals with similar active ingredients may vary in overall ability to inactivate virus, thus generalizations should not be made among products perceived to be similar in chemical formulation.