Most disinfectants won't work if the surface to be disinfected isn't
clean before applying the disinfectant.
Steam and high-pressure washers can be very useful to clean porous surfaces.
Organic materials such as soil, plant debris (like straw), milk, blood, pus,
and manure often inactivate some disinfectants or protect germs from the
disinfectant's active ingredients. Chlorine-based disinfectants are
especially subject to 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. 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.
Disinfectants also vary considerably in their activity against the assorted
germs bacteria, viruses, fungi, and protozoa about which livestock producers
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
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.
These conditions include 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.
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 of
a dirty boot in a foot bath is not likely to accomplish anything except to
give a false sense of security.
Add 3 gallons of chlorine bleach to 2 gallons of water; mix thoroughly.
Add 6.5 ounces of glacial acetic acid to 1 gallon of water; mix thoroughly.
Vinegar is a 4% solution of acetic acid.
Peroxymonosulfate and Sodium Chloride (i.e., Virkon-S)
Follow label directions.
Sodium Carbonate (soda ash)*
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.
||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. <http://www.aphis.usda.gov/oa/pubs/fco412.pdf>
As you can see from the 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.
On most farms, disinfectants will be used in foot baths or for cleaning
equipment and livestock premises. The most commonly used disinfectants fall
into the following classes.
Quaternary ammonium. 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. Compounds in this class usually have some detergent
action; however, they are usually inactivated in contact with many soaps or
Phenol-based compounds. These compounds are coal-tar derivatives and often
have a strong pine-tar odor. They usually turn milky when added to water and
have good activity in hard water and in the presence of some organic
material. They are considered active against many bacteria, viruses, and
fungi, including the bacteria that cause tuberculosis and Johne's disease.
They are not especially active against the FMD virus; however, they are good
all-purpose disinfectants for farm use. Some examples of this class of
disinfectants include One Stroke Environ®, Osyl®, and Amphyl®.
Hypochlorites. Chlorine compounds are good disinfectants on clean surfaces
and have a broad spectrum of activity. They generally are more active in
warm water. They can be somewhat irritating and can be harmful to clothing,
rubber goods, and some metals. Some of the newer chlorine-based
disinfectants are complex molecules that are less irritating and more
effective than older ones such as bleach and Halazone®. Chlorine-based
disinfectants are generally compatible with soaps but should never be mixed
with acids. Their activity is strongly reduced by the presence of organic
matter. Many chlorine solutions are unstable and need to be frequently
replaced; read the label.
Iodophors. Iodine compounds have been used as antiseptics and disinfectants
for many years. The iodophors are combinations of iodine and another
molecule that makes them water-soluble. They are good disinfectants but are
also not as effective in the presence of organic debris. Iodophors are
generally less toxic than other disinfectants but can stain clothes and some
surfaces. They are inactivated in the presence of some metals and by
sunlight. They should not be mixed with quaternary ammonium disinfectants as
they will be inactivated. Some examples of this class are Betadine® and
Newer compounds. New disinfectants are being introduced regularly. Some of
these are oxidizing agents. Virkon S® is a peroxygen molecule/organic
acid/surfactant combination (surfactants reduce surface tension to help
water-based compounds penetrate). 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, etc. Another compound, based on peroxyacetic acid, is
Oxy-Sept 333®. It is now EPA-approved for foot-and-mouth disease virus and
is reportedly active against a broad spectrum of germs.
Remember, disinfectants are not to be applied to animals directly, unless
labeled for such use, and you should consult the label to make sure there
are no warnings against using them around feeders and in animal quarters. A
general recommendation is to rinse disinfectants off after the appropriate
amount of contact time if animals will have contact with the disinfected
surfaces. Label directions should be strictly followed, and different
classes of disinfectants should not be mixed.
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 the disinfectant
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.