Dry Disinfectant Effective Against PRRSv For Internal Biosecurity

Researchers at the University of Minnesota wanted to test a specific dry disinfectant powder, as an alternative to a liquid disinfectant boot bath, for the deactivation of PRRSv under various temperatures and in the presence or absence of fecal matter. The main objective was to evaluate this type of product in an internal biosecurity program.

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Trial 1 involved clean, dry rubber boots that were randomly assigned to treatments of boot baths containing either dry disinfectant powder or a quaternary ammonia/glutaraledehyde liquid disinfectant. The bottom of each boot was sampled at environmental temperatures of both 85°F and 8°F and analyzed by PCR to verify the absence of virus. Reconstituted commercial PRRS MLV vaccine was applied to the bottom of each boot at a dilution that was equivalent to a typical infectious dose of PRRSv via oral and intranasal routes. The inoculated boot was then sampled and tested by PCR to confirm presence of the PRRSv. PRRSv inoculated boots were then placed in either the dry or liquid boot bath in order to simulate on farm conditions. The boots were sampled and tested by PCR at 1 minute post-disinfection. The sensitivity of PRRSv PCR testing at this dilution of vaccine plus neutralizing broth and method of collection were validated by submission of 5 positive inoculated samples to two independent diagnostic laboratories.

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Trial 2 involved mixing 2 mL of commercial PRRS MLV vaccine of the same dilution into a quarter cup of confirmed PCR negative fecal matter. Fecal matter was then applied to the bottom of each boot, sampled, and tested by PCR to confirm the presence of the virus. The PRRSv inoculated boots were consecutively placed in each boot bath per treatment group and the bottoms of the boots were sampled and tested by PCR 1 minute post-disinfection. This trial (with and without fecal matter) was then repeated with sampling after 3 min. and 5 min post-disinfection. A sample of each boot bath was taken at the completion of each treatment group and tested by PCR.

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In trials 1 and 2, neither of the products tested resulted in 100% PRRSv PCR negative results under all conditions. Increasing exposure time did not improve the effectiveness of either disinfectant. The presence of fecal matter significantly reduced the effectiveness of liquid quaternary ammonium/glutaraldehyde liquid disinfectant but had no significant effect on the dry disinfectant powder. In the absence of fecal matter, the liquid quaternary ammonium/glutaraldehyde liquid disinfectant appeared to be more effective compared to the drying powder.  At 8°F and 85°F the drying powder showed no significant difference in effectiveness with or without fecal matter with an average of 95.8% and 86.2% PCR negative samples respectively, under the conditions tested at both temperatures. The liquid disinfectant was frozen at 8°F making it ineffective at deactivating PRRSv under the conditions tested at that temperature. At 85°F the liquid disinfectant generated an average of 97.3% PCR negative samples without fecal matter and only 28 % PCR negative samples with fecal matter present respectively, under the conditions tested at that temperature.

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Take Home Message:

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1. Danish entry protocol with change of boots between positive and negative populations continues to be the most consistently method to reduce the spread of PRRSv.
2. The liquid quaternary ammonium / glutaraldehyde disinfectant was the most consistently effective disinfectant when fecal matter was removed and where temperatures were ideal.
3. The dry disinfectant powder, however , was demonstrated to be a viable alternative to the liquid disinfectant as a disinfectant boot bath and offers advantages to liquid disinfectant boot baths where fecal matter and freezing temperatures are an issue. The dry disinfectant powder boot bath can be considered for use in internal biosecurity programs such as McRebel where boot changes are not practical.

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Ref:  An evaluation of Stalosan  F powder for deactivation of PRRSv AASV 2012   Annual Meeting: Integrating Science, Welfare and Economics in Practice Rabbe C.; Murray D.,  Sponheim A.