Virucidal Efficacy of Four New Disinfectants
Virucidal efficacy was evaluated for four recently available disinfectants: chlorine dioxide, potassium peroxymonosulfate, a quaternary ammonium compound, and citricidal (grapefruit extract). Sodium hypochlorite (3%) and tap water were used as positive and negative controls respectively. Feline herpesvirus, feline calicivirus, and feline parvovirus were exposed to the manufacturers’ recommended dilutions of the evaluated disinfectants. Both chlorine dioxide and potassium peroxymonosulfate completely inactivated the three viruses used in this study. These disinfectants can aid in controlling nosocomial transmission of viruses with less of the deleterious effects of sodium hypochlorite. The quaternary ammonium compound evaluated in this study and citricidal were not effective against feline calicivirus and feline parvovirus.
Introduction
Nosocomial transmission of viruses at animal facilities contributes to spread of disease and increased veterinary medical costs.1–3 Enveloped viruses are efficiently inactivated by lipophilic disinfectants such as detergents and the quaternary ammonium compounds (QAC).3 Hydrophilic, nonenveloped viruses such as parvoviruses are resistant to most common disinfectants.1245 The halogens and aldehyde disinfectants efficiently inactivate these resistant viruses, but they are corrosive and toxic.13 Although many QAC have claimed broad-spectrum virucidal activity, several studies have indicated poor efficacy against certain nonenveloped viruses.15 In this study, the authors investigated the virucidal efficacy of four new disinfectants: chlorine dioxide, potassium peroxymonosulfate, one of the QAC, and citricidal. These disinfectants have been marketed for general use in veterinary clinics or aviaries. Most have claimed broad antimicrobial specificity. Feline herpesvirus, feline calicivirus, and feline parvovirus were used because of their graded resistance to disinfectants (from susceptible to highly resistant, respectively).
Materials and Methods
Viruses
Field isolates of feline herpesvirus, feline calicivirus, and feline parvovirus were obtained from the Clinical Virology Laboratory, College of Veterinary Medicine, University of Tennessee. The viruses were propagated on Crandel feline kidney cells (CRFK)a using DMEMb supplemented with 5% fetal bovine serum.c Virus inocula were prepared by rapid freezing and thawing of infected cell culture suspension, followed by centrifugation for 15 minutes at 2,000 × g to remove cellular debris. The supernatant was removed and stored at −80°C. Titration of each of the three viruses was done according to standard methods.6 The original titers of feline herpesvirus, feline calicivirus, and feline parvovirus stock solutions were 5 × 105, 5 × 106, and 5 × 104/mL cell culture infectious doses (CCID50), respectively.
Disinfectants
Four disinfectants including chlorine dioxide (A),d potassium peroxymonosulfate (B),e QAC (C),f and citricidal (D)g were used for evaluation of their virucidal efficacy [Table 1]. Tap water was used as a negative control and 3% sodium hypochloriteh as a positive control. Table 2 represents efficacy of the used disinfectants according to manufacturers’ claims.
Experimental Procedure
Solutions of disinfectants were prepared by dilution with tap water to twice (2×) the manufacturers’ recommended concentration for disinfection. For D, the authors followed the manufacturer’s recommendations for usage as an all-purpose cleaner. Each disinfectant dilution (2×) was mixed with an equal amount of each virus stock, resulting in the recommended concentration of each disinfectant (1×). Mixtures of equal parts of virus stock and tap water were used as negative controls of the experiment. These mixtures were held for 10 minutes at room temperature5 and then transferred into dialysis tubing.i Dialysis against five changes of Hank’s balanced salt solutionj with sodium bicarbonatej was done for 48 hours at 4°C to eliminate the possible toxic effect of disinfectants on cell culture used for virus titration.5 Tenfold serial dilutions of the preparations were made and then filtered through 0.2-μm membrane filters to remove any possible bacterial contamination and stored at −80°C. Virus titers (CCID50) of these dilutions were measured according to the standard method.6 Cytopathic effect on cell culture followed by confirmation with immunofluorescence test3 was used for virus detection. Four replicates of each virus/disinfectant dilution were performed.
Results
The residual virus titers (CCID50) following exposure to disinfectants and dialysis are shown in Table 3. Exposure of the viruses to tap water (the negative control) had no detectable effect on the virus titer, indicating that the experimental design itself did not affect virus viability. Sodium hypochlorite completely inactivated the three viruses used in this study. Both A and B completely inactivated feline herpesvirus, feline calicivirus, and feline parvovirus. Disinfectant C partially inactivated feline parvovirus and did not affect feline calicivirus. Disinfectant D only inactivated feline herpesvirus and had no effect on feline calicivirus and feline parvovirus.
Discussion
Previous studies indicate that nonenveloped viruses (parvoviruses in particular) are resistant to most commonly used disinfectants.1245 The results of this study indicate that disinfectant C partially inactivated feline parvovirus and had no effect on feline calicivirus. This data is similar to the results of a previous study on the virucidal efficacy of QAC disinfectants.5 Disinfectants A and B were effective for inactivation of both feline calicivirus and feline parvovirus used as models of nonenveloped viruses. Their efficacy against these viruses was the same as that of sodium hypochlorite. However, disinfectants C and D were not effective for disinfection of feline calicivirus and feline parvovirus. In considering the two effective disinfectants, A is nontoxic, hypoallergenic, and less corrosive for steel instruments and surfaces according to the manufacturer.d For disinfectant B, a 1% working solution is not corrosive for good-quality medical instruments but is corrosive for low-quality instruments according to the manufacturer.e Manufacturers’ directions for using A and C for disinfection of nonporous, hard surfaces require 10 minutes at least as a contact time, while directions for disinfectant B do not specify a contact time. Therefore, the authors used 10 minutes as a contact time for each disinfectant in this experiment. However, this 10 minutes contact time may be longer than what actually occurs in some applications of disinfectants, as in cage cleaning. Also, the presence of organic materials such as blood and feces may affect the degree of contact between disinfectants and microorganisms.
Conclusion
Disinfectants A (chlorine dioxide) and B (potassium peroxy-monosulfate) can aid in controlling nosocomial viral infections, when following manufacturers’ directions, and in decreasing veterinary medical costs with less of the deleterious effects of sodium hypochlorite. However, disinfectants C (QAC) and D (citricidal) were not effective for that purpose.
American Type Culture Collection, Rockville, MD
Dulbecco’s Modified Eagle’s Medium; Bio-Whittaker, Walkersville, MD
Gibco-BRL, Gaithersburg, MD
Dentagen; Oxyfresh Worldwide, Inc., Spokane, WA
Trifectant; Antec International Limited, distributed by Veterinary Products Laboratories, Phoenix, AZ
A33; Airkem Professional Products, Division of ECOLAB, Inc., St. Paul, MN
Nutribiotic; Nutribiotic Co., Lakeport, CA
By dilution with water
Nominal MW Co., 12,000-14,000; Fisher Scientific, Pittsburgh, PA
Mediatech Inc., VA, AK, HI
