Virus-Dependent Relative Contributions of Citric Acid and Benzalkonium Chloride to the Virucidal Efficacy of Combination Disinfectants

Chemical disinfectants used in livestock production commonly combine citric acid (CA) and benzalkonium chloride (BZK), yet the respective contributions of these active ingredients to virucidal efficacy remain poorly understood. This study quantified the relative contributions of CA and BZK against the non-enveloped foot-and-mouth disease virus (FMDV) and the enveloped avian influenza virus (AIV). Virucidal efficacy was evaluated using a full-factorial design comprising six CA concentrations and six BZK concentrations at contact times of 3 and 30 min. Log reduction values (LRVs) were analyzed by two-way ANOVA and multiple linear regression, and the relative importance of each predictor was estimated using the Lindeman–Merenda–Gold (LMG) method. FMDV inactivation was primarily determined by CA, which accounted for 99.99% and 99.87% of the explained variance at 3 and 30 min, respectively, whereas BZK and the interaction term contributed minimally. In contrast, BZK was the dominant determinant of AIV inactivation, explaining 69.79% and 78.02% of the variance at 3 and 30 min, respectively, while CA made a smaller contribution. These findings demonstrate that the dominant active ingredient in CA–BZK combination disinfectants differed markedly between the FMDV and AIV models examined. Quantifying the relative contribution of individual components provides a basis for the rational formulation and optimization of veterinary disinfectants for different target viruses.