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Disinfectants: The Rotation Myth

by 5m Editor
24 July 2006, at 12:00am

By Luc Ledoux, CID LINES nv - Forget the old myth is that you need different disinfectants for different applications and that they should be rotated regularly. Rotation is not only unnecessary with modern disinfection products, it also leads to a logistics nightmare and increases the chances of human error.

CID Lines

The rotation myth comes from the days when pig producers used single, often unformulated raw ingredients for their pen hygiene routines. They were advised to rotate the disinfectant in other words, change to another type from time to time because of a risk of resistance. Using ingredients that did not kill the full spectrum of microbes raised the possibility that some bugs could remain after disinfection and develop a tolerance to the cleaning agent employed against them.

This could occur, for example, from the use of iodine alone as a disinfectant. Iodine does not kill all types of viruses, so they would be able to proliferate unchecked. Pure quaternary ammonia or phenols when used on their own will allow naked viruses and spore-forming bacteria to survive.

But the carefully formulated, synergistic combination products of today are very different. A good broad-spectrum disinfectant will not need to be rotated, provided that it is designed to work in the circumstances of a typical pig house.

What criteria must a disinfection product meet, to be suitable for pig-unit application and to rule out rotation? I would list the requirements as a full spectrum of activity that has been verified independently, a synergy of components, good buffering, versatility, a residual action and guaranteed composition.

Activity against a full spectrum of potential health challenges means the disinfectant should kill all types of micro-organism. So it has to be a bactericide, a virucide, a fungicide and a sporicide. Furthermore, its range of activity must include the most difficult microbes to kill (fungi such as Candida albicans and spore-forming bacteria like Clostridia).

Viruses present the major threat to pig health, so a proven virucidal action is an obvious necessity. Suppliers' claims for their disinfectant should be backed by scientific evidence that it kills some harsh viruses, whether these are encapsulated or 'naked'. Examples of a virus that has its own protective capsule include the agents of Aujeszky/pseudorabies and classical swine fever/hog cholera, whereas foot-and-mouth disease and others of the Picornaviridae group come in the non-capsule category.

Generally the naked viruses are more difficult to eliminate, so they should figure on the claim! A most important requirement, given the topical importance of circovirus-related diseases, is that the disinfectant acts against the PCV2 porcine circovirus. Not all products do this because it is extremely difficult to kill.

On the question of proof, different testing methods are used to verify a claim. Virtually every country has its own system, most often identified by a set of initials. In France there is AFNOR, the British have DEFRA, the Germans DVG, the Americans AOAC, while the European Union refers to a European Norm or EN. Some of the national tests (like the UK's) are done in rather in vitro situations at a laboratory. Others, like the Association Of American Chemicals or AOAC test in the United States, require very harsh conditions in terms of organic load (> 5%) and water hardness (> 400ppm) which are closer to the circumstances met in practice inside pig housing.

Synergy means that the total effect is greater than the sum of the parts. It can be achieved by combining certain ingredient types in a certain ratio. A good example is a well balanced combination of alcohol, quaternary ammonia and aldehydes. In the case of bacteria, the alcohol helps to remove the fat and organics from the cellular wall. The quaternary ammonia then penetrates better through that wall, opening the way for a non-carcinogenic aldehyde like glutaraldehyde to move inside the cell and kill the nucleus. Possibilities exist to create an internal synergy for further impact within this overall scheme by combining single-chain and twin-chain quaternary ammonia sources.

Buffering may seem a strange term, but the great secret of disinfectants is how to buffer them so their active ingredients are not affected by antagonistic chemistry. Plain chlorine is an example of a non-buffered ingredient: it becomes inactivated by organic matter (which is why swimming pools need to add chlorine continuously). The necessary buffering can be obtained by chelating agents. Some other buffers inhibit corrosion. However, the active ingredient of a disinfectant can corrode metal equipment or a concrete floor if it is very acid or extremely alkaline.

Good disinfectants work equally well even in hard water, not being neutralised by calcium carbonate and other minerals. For this property they contain sequestering agents. Also make sure your product contains wetting agents or surfactants to give them enough penetration power, especially through residues of organic matter or if the surface is still wet. It remains true nevertheless that the better the cleaning job done before disinfection, the better the disinfectant will work. Buying both cleaning agents and disinfectants from the same supplier ensures they are compatible.

The shelf life of a product should be sufficient to keep it in stock for at least 2 years. Products like chlorine are very volatile and have a limited shelf life: bleach will not last longer than 6 months. Where bleach is used in disinfecting, therefore, stocks would need to be rotated to ensure the chemical was still effective.

Versatility in effect means the disinfectant is ready to use for different applications. A versatile disinfectant should be applicable by spraying, by foaming (requiring a foam lance) and by fogging. The addition of a special carrier would be required for application by thermo-fogging, however, which raises the possibility of human error in adding it correctly. It should be the job of the manufacturer to formulate chemicals, not of the end-user!

Mixing wrong chemicals can be dangerous. The only thing the end-user should do is dilute a product with water. Remember that liquids mix easier with water than powders. Check the dilution rate with the label and against the product concentration: the higher amount of (synergistic) ingredients in grams per litre, the lower the dilution.

Residual action means that the product should last a certain time, preventing microbiological recontamination. In the case of fumigation with formaline the residual action is close to none. But a well formulated product should last for several days after being used to fog a house.

Guarantees given by the manufacturer refer to certain certifications such as ISO and GMP (Good Manufacturing Practice). These oblige the manufacturer to "do as he says and say as he does". It guarantees that the claims are genuine and that what is on the label is also inside the drum.

The disinfectant of choice for a pig unit has all the above mentioned characteristics and, on top of that, it is not corrosive. It can be used not only to disinfect rooms, pens and equipment, but also to ensure trucks are clean and in dips for wheels and boots.

Furthermore, a good disinfectant with a full spectrum of activity (well proven by scientific tests) completely dispels the rotation myth described at the start of this report. Resistant or tolerant bugs are not an issue with such a product so there is no need to rotate it. That has to be good news for the management of any herd. Using one universal disinfectant will simplify the herd's logistics of chemical storage and minimise the risk of human error.

Source: CID LINES - June 2006