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Disinfection in on-farm biosecurity procedures

by 5m Editor
25 May 2001, at 12:00am

By Dr. William Shulaw, Department of Veterinary Preventive Medicine, The Ohio State University - In recent weeks the appearance of foot-and-mouth disease (FMD) in Europe, and its possible introduction into the United States, has caused many livestock owners serious concern. So much so that many are now looking more closely at their biosecurity plans or their efforts to keep the disease out of their herds. This article provides some practical advice about disinfectants.

We have received many calls regarding which disinfectants to use on shoes, boots, tires, or other equipment in order to kill the foot-and-mouth disease virus.

Important points

A few important points about disinfection should be made before choosing a disinfectant for routine farm use. First, most disinfectants won't work if the surface to be disinfected isn't fairly clean before applying the disinfectant.
Activity
Organic materials such as soil, plant debris (such as straw), milk, blood, pus, and manure often inactivate some disinfectants or protect germs from the disinfectant's active ingredients. Chlorine-based disinfectants are an example of this problem. Chlorine, the active ingredient in bleach, is relatively quickly inactivated by organic debris such as manure, and even milk, at the concentrations usually used on clean surfaces. In addition, even "hard" water can reduce or destroy the activity of some disinfectants. Likewise, some disinfectant solutions are only active for a few days after mixing or preparing.
Keep fresh
Failure to make a fresh solution of disinfectant after it has been prepared longer than a few days, or after it has become visibly contaminated by organic material like manure, may result in using a product that doesn't really work. Even worse, it may give a false sense of security. It is true that sufficient concentration and contact time can overcome some of these problems with certain classes of disinfectants, but often increasing the concentration or contact time makes use of the product impractical, costly, or caustic.
Correct disinfectant
Disinfectants also vary considerably in their activity against the assorted germs (bacteria, viruses, fungi, and protozoa) that livestock producers are concerned about. For example, plain vinegar (4% acetic acid) will readily kill the foot-and-mouth disease virus, but it won't do much to Mycobacterium paratuberculosis, the cause of Johne's disease. Most commonly used disinfectants are not active against bacterial spores, the environmentally hardy life-form taken by the germs that cause tetanus, blackleg, botulism, and anthrax. Yes, formaldehyde is effective against most spores, but it is not really a practical disinfectant and is now considered a potential cancer-causing compound.
Selection
It is important to select a disinfectant that will be active across a wide spectrum of germs under the conditions in which it will usually be used; this includes hard water, contamination with organic material, and potential for toxicity or damage to environmental surfaces or skin and clothing. It is also important to keep solutions clean and freshly made as directed by the manufacturer.
Contact time
Lastly, disinfectants must have sufficient contact time with the surfaces to which they are applied in order to allow them to kill the germs with which we are concerned. Contact time needed varies with the product and the germ. A quick splash in a foot bath with a dirty boot is not likely to accomplish anything except to give a false sense of security.

Foot-and-mouth

The following chart of disinfectants has recently been made available by the USDA for field use in a foot-and-mouth disease outbreak **:

Product

Dilution

Mixing Instructions Notes
5.25% Sodium Hypochlorite
(NaOCl)
(household bleach)


3%
Add 3 gallons of chlorine bleach to 2 gallons of water, mix thoroughly.
Acetic acid*

4-5%

Add 6.5 ounces of glacial acetic acid to 1 gallon of water, mis thoroughly. Vinegar is a 4% solution of acetic acid
Potassium

Peroxymonosulfate and Sodium Chloride
(i.e. Virkon-S)

1%

Follow label directions. Virkon-S
Sodium Carbonate (soda ash)*

4%

Add 5.33 ounces of sodium carbonate to 1 gallon of hot water (or 1 pound to 3 gallons of hot water), mix thoroughly. The solution is mildly caustic, but can dull paint and varnished surfaces.


Sodium Hydroxide (NaOH)
(lye)*

2%

Add 1/3 cup of NaOH pellets (2.7 ounces of the lye) to 1 gallon of cold water, mix thoroughly. This solution is highly caustic, use protective rubber clothing, gloves and safety glasses.
WARNING: Always add the lye to the water. Never pour the water over the lye.
* Section 18 application submitted and EPA approval is pending.
**From National Emergency Response to a Highly Contagious Animal Disease, Executive Summary, March 30, 2001

As you can see above, common household bleach would be an effective disinfectant for the FMD virus, but the recommended concentration (3% sodium hypochlorite) is 60% of full strength as it comes from the bottle. This concentration would damage clothing, shoes, and rubber goods, and is mildly corrosive to steel surfaces. It can be used on an infected premise for FMD, but probably wouldn't be a good choice as a general purpose disinfectant for equipment and foot baths.

Vinegar will also kill the virus, but wouldn't be a good choice for general use because of its lack of effectiveness against many other important germs. Obviously, lye is too caustic for general use.

Next step

So, where do we go from here? On most farms, disinfectants will be used in foot baths or for cleaning equipment and livestock premises. The older quaternary ammonium compounds (Roccal DT) are good for some situations and relatively clean surfaces. They will not be particularly effective against FMD or M. paratuberculosis, the cause of Johne's disease, and have markedly reduced activity in the presence of organic material. Some of the newer quaternary ammonium preparations have improved activity. Chlorhexidine (NolvasanT) is a widely used disinfectant/antiseptic that is easy on skin surfaces but can be inactivated by organic debris and hard water. It is useful for clean surfaces and some instruments.

For foot baths, boots, and some equipment the phenolic-based compounds, such as One Stroke EnvironT, OsylT, and AmphylT, have good activity in hard water and in the presence of some organic material. They are considered active against the germs that cause tuberculosis and Johne's disease but are not very active against the FMD virus.

Virkon ST is an organic acid/surfactant combination, and it appears to have a wide spectrum of activity against many kinds of germs (including the FMD virus). It is relatively stable in the presence of some organic material. It has a pH of around 2.6, when mixed as directed, but is labeled as nonirritating to skin. It is advertised as useful on many kinds of equipment, including saddles, brushes, buckets, and etc. Again, the contact time needed for effective disinfection will vary with the product used and must be a consideration in your choice. Disinfectants are not to be applied to animals directly, and you should consult the label to make sure there are no warnings against using them around feeders and animal quarters.

In the event of a foreign animal disease outbreak, such as FMD, the type of disinfectant and procedures used in the cleanup of infected farms and for routine prevention activities will be selected by regulatory officials.

For routine use in biosecurity programs at the farm level, producers should consider the major risks they are concerned about, consider the type of surface they wish to disinfect, the conditions under which it will be used, and then select a disinfectant that best suits their needs.

Information about activity in hard water or in the presence of organic debris, contact time needed, what germs are reliably killed, human use and environmental concerns, and other details are usually on the label or can be obtained from the company. Web sites are often good sources of information about individual products. Above all, producers should remember that disinfection is just one aspect of their biosecurity program.

Further Information

For further information on disinfection and biosecurity
BROWSE or SEARCH our Pig Health Database

The following feature articles are also available on these topics:

Disinfection From Top to Bottom

Disinfection of Swine Barns

About Aerial Disinfection

Two Aerial Disinfection Programmes


2001