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Applying science to disinfecting

The cleaning and disinfection process are critical steps in any biosecurity program in order to minimize the transmission of diseases. Washing is the most critical step of the entire process. This step will remove over 99% of the microorganisms.
Thursday 10 September 2009 (8 years 9 months 8 days ago)
joeust
The cleaning and disinfection process are critical steps in any biosecurity program in order to minimize the transmission of diseases. This process involves several steps we will evaluate as well as discuss their importance.

Cleaning

Although this seems to be very basic, it is a critical step. One must remove all dirt, bedding, large amounts of feces, leftover feed, and any other organic material from the area. Usually one must start by using brooms , shovels, scrapers, and tipping over feeders. Getting rid of the large organic matter will minimize water usage in the next step as well as minimize the dispersion of all this material with the high pressure water. With our modern facilities, this step is quite simple and usually involves dumping out all feeders as well as pulling the plugs in the pits or running the manure scraper system if applicable. The main goal of this step is to remove the most amount of contaminated material.

Washing

This is the most critical step of the entire process. This step will remove over 99% of the microorganisms. High pressure (e.g. 2,000 psi) hot water is the most effective in facilitating this process. Having higher volumes of water per minute (e.g. 4 gpm) is also important. For even better results, detergents can be used. Detergents are specially designed products that reduce surface tension and suspend particles from the surface facilitating the cleaning. Detergents can be cationic (positively charged), anionic (negatively charged, or non-ionic (no charge).


Picture 1. Fully cleaned and washed nursery ready to be disinfected.

Disinfection

The disinfection process will only be effective if the previous washing step was effective in removing all the organic materials. Most of the disinfectants are inactivated by organic material, or if still active, they do not have the power to penetrate large amount of organic material and thereby are unable to do their job (kill microorganisms). In the U.S. all disinfectants are resisted by the Environmental Protection Agency (EPA) as "antimicrobial peptides." It is a federal law violation to use a disinfectant in any way other than how they are labeled.


Picture 2. Foot bath freshly stocked with proper phenolic disinfectant.

To select the proper disinfectant one must know the target organism. Table 1 summarizes the general characteristics of each class of disinfectant. Table 2 summarizes the effectiveness of the different classes of disinfectants on different types of microorganisms. When a swine producer asks me "what disinfectant should I be using Doc?" My answer is always: "Well what are you trying to prevent?"

Table 1. General characteristics of different classes of disinfectants.
ADVANTAGES DISADVANTAGES
Acids (acetic acid, citric acid)
Destroy nucleic acid bonds Caustic
Precipitate proteins Can be toxic in air at high concentrations
Activity is pH dependant
Limited use
Alcohols (isopropyl and ethyl alcohol)
Denature proteins --> cell lysis Fire hazard
Non-corrosive Isopropanol is not effective against non-enveloped viruses
Effective at 70 - 90% concentrations
Aldehydes (formaldehyde, gluteraldehyde)
Denature proteins Formaldehyde is carcinogenic (gluteraldehyde is considered safe by EPA)
Disrupt nucleic acids Slight to moderately effective with organic matter
Non-corrosive
Slight residue activity
Alkalis (lye, ammonium hydorxide, quicklime)
Saponify lipids in enveloped organisms Slow activity that increases with temperature
Very corrosive
Sodium hydroxide (lye) is effective against FMD
Biguanides (chlorhexidine)
Alter cell permeability Easily deactivated by soaps, detergents, and hard water
Relatively non-irritating to skin Toxic to fish
Halogens (chlorine or iodine compounds)
Denature proteins Lose potency with time, organic matter, and sunlight
Household bleach is 5.25% Sodium hypochlorite Never mix hypochlorites with acids or ammonia
Inexpensive High concentrations can irritate skin
Oxidizing agents (hydrogen peroxide, peracitic acid)
Denature proteins May be irritating in high concentrations
Denature lipids Moderately corrosive
Phenols
Denature proteins Not effective against non-enveloped viruses
Alter cell wall permeability Concentrations over 2% can be highly toxic to animals especially cats
Good effectiveness with organic matter (foot baths – see Picture 2)
Have milky or white color when added to water
Maintain activity in hard water
Have residue after drying
Quaternary ammonium compounds (quats or QAC)
Denature proteins Not effective against non-enveloped viruses
Change cell permeability Inactivated by organic matter, detergents, soaps, and hard water
Toxic to fish

Table 2. General antimicrobial spectrum of disinfectants (adapted from CFSPH*).
Acids Alcohols Aldehydes Alkalis Biguanides Halogens Oxidizing agents Phenolic comp. Quaternary ammonia comp.
Mycoplasm. + ++ ++ ++ ++ ++ ++ ++ +
Bacteria + ++ ++ + ++ + + ++ +
Enveloped viruses
(e.g. PRRS)
+ + ++ + +/- + + + or +/- +/-
Non-enveloped viruses
(e.g. PCV2)
- - + +/- - +/- +/- - -
Spores +/- - + +/- - + - or + - -
Coccidia - - - - or + - - - - or + -
++Highly effective +Effective +/-Limited effectiveness -No activity NA Data not available
*Center for Food Security and Public Health at Iowa State University

There is a science to deciding which product you need to use. It is exactly the same process we use in antibiotic selection although in the case of disinfectants we can target both bacteria and viruses. There is no one product that will be effective against all swine pathogens. There is also no scientific evidence to support the idea of rotating disinfectants to prevent resistance building. Disinfectants work in completely different ways than antibiotics.

Disinfectant need to be applied to all surfaces in the proper concentration. Read your product label. Using higher concentrations does not necessarily increase the effectiveness of the product, but rather can double or more your cost of the process. Many disinfectants are now approved to be applied as foams. This process ensures that all surfaces are disinfected adequately and allow longer contact time.

It is critical to remember that all disinfectants need contact time to be effective. The industry standard is 10 minutes. This means that disinfectant need to be in contact with surfaces for at least 10 minutes for them to be effective.

Drying

All microorganisms are living organisms and therefore need water to survive. Allowing surfaces to completely dry is the last effective step in making sure we kill most of the remaining microorganisms. In swine production units this is always a hard step. Farrowing rooms are filled back in soon after the disinfection process has occurred and the room is still wet. On the other hand, nursery and finishing facilities usually are allowed to dry before restocking. In the farrowing house, even giving one day to totally dry two or three times a year may be all you need to help break that disease transmission cycle.

The objective of the cleaning and disinfection process is simple: minimize the bacterial/viral contamination to which pigs are exposed. This lower load of organisms can prevent infection or be low enough to allow the pig's immune system to better fight off the diseases.

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Victor17-Sep-2009 (8 years 9 months 1 days ago)

Very interesting article. Is the use of foot baths before going into the barn (nursery, farrowing) an effective method to prevent contamination. In this case, the contact time of the desinfectant is low. What are your recommendations

Alex Ramirez26-Sep-2009 (8 years 8 months 23 days ago)

Victor you are correct in your observation. Foot baths can be helpful if the boots are fully cleaned with water and scrub brush before being placed in the bath. The cleaning and washing is what helps the most with the disinfectant being a secondary backup. Contact time can be an issue, but for practical purposes we don't have a better option. Studies have shown that if you do not clean your boots, you can stand in the boot bath for 5 minutes and really have no impact on the bacterial load. So in summary, just having a hose and brush is a good option.

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