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Disinfection

(53) Disinfectants are substances that kill both harmless and disease producing organisms. They act either as bacterial poisons, coagulate bacterial protein or act as oxidising or reducing agents. Antiseptics normally prevent bacterial multiplication and are used for cleaning skin or wounds. Some disinfectants in a more dilute form may act as antiseptics.

Common antiseptics used include:

  • Chlorine based ones such as TCP.
  • Quaternary ammonium compounds such as cetrimide
  • Chloroxylenol (dettol).
  • 1% crystal violet.
  • Iodine.
  • Alcohol
  • 1% salt solutions.
  • Hydrogen peroxide.
Disinfectants have two prime functions. First to prevent infectious agents gaining access to the farm and second equally important to control those organisms already on the farm and that persist in large numbers in the environment. The process of disinfection can be considered in three stages.
  1. The removal of the gross contamination within the building, that is the dried faeces, slurry and dust, by pressure washing preferably with hot water.
  2. The use of detergents to assist in the final removal of the organic material. Only after completion of these two should a disinfectant be applied.
  3. The use of the disinfectant.

Remember that the cheapest methods of disinfection are the physical removal of contaminated material and final removal by water.

The effects of this are illustrated by a case of poor growth in finisher pigs. Two houses were involved, neither of which had been emptied or washed out for two and a half years. As an experiment groups of pigs were split into two on entry into the houses and weighed in and out again at point of slaughter. One of the houses was divided into sections and used on an all-in all-out basis. It was completely washed prior to the entry of each batch of pigs and the other house was used as a control with no changes. The growth curves of both groups were compared and by point of slaughter at 90kg there was approximately a nine days difference to the obvious advantage of the cleaned house. It is interesting in this case that only water and detergents were used without disinfectants. The all-in all-out procedures will also have contributed to the performance.

This phenomena of all-in all-out production associated with cleaning has been well known for a long time and yet on many farms it is still not practised. The reasons for the improved efficiencies are now better understood. In this study the pigs were no longer coming into an environment in which there was endemic disease. This was maintained by aerosol droplet infection from other pigs in the building and enteric organisms on floors and walls. The cleaned building was empty for periods of four days during and after the cleaning process and all the respiratory droplet organisms had time to be ventilated or precipitated from the air space. Whenever a pig enters an environment with older pigs already in the house, the large numbers of organisms present challenge the immune system of the incoming pigs and this process uses large amounts of protein and energy. This has effect of decreasing daily gain and food conversion efficiency whether serious specific diseases are present or not. This is a very important lesson to learn.

Colitis (inflammation of the large bowel) in growing pigs is now a common occurrence on pig farms. One of the major contributing factors is the continual use of pens, without washing and cleaning between batches.

Disciplines are almost invariably maintained in farrowing houses through all-in all-out procedures and by washing and disinfection. The same principles should apply equally across all pig buildings on the farm and in particular the mating area and the finishing houses. On many farms the mating pens have been in continual use for 25 years and we often wonder why reproductive performance has dropped gradually over intervening periods from farrowing rates of 90% to 80%. Other areas that require constant cleaning are foot dips and hands after handling diseased pigs. When a litter of young pigs have been treated for scour, the hands and clothing become heavily contaminated by as much as 15 to 20 billion organisms. (0.5m to 3 million will produce scour in the piglet).

Facilities for washing and disinfecting hands to prevent the spread of infection should become an important part of environmental control.

Properties of a good detergent

  • It should be efficient in removing organic material.
  • Acts well in pitted surfaces.
  • Has a good degreasing action.
  • Good penetration.
  • Quick acting.
  • Works in the presence of the disinfectant.
  • No residues are left.
  • Active with hard water.
  • Non toxic.
  • Does not make floors slippery.
A recommended routine for cleaning houses
  1. Remove all muck and empty all slurry channels, tanks and gulleys.
  2. Isolate the electricity supply.
  3. Disconnect all moveable equipment, feeders, lamps etc. and open all inaccessible areas e.g. channels, fan boxes etc.
  4. Brush down and sweep out the house.
  5. Soak the complete building, roof to floor with a farm detergent or water, for 24 hours if possible.
  6. Soak all moveable equipment and clean down.
  7. Drain and flush out the water system, bowls, nipples, water tanks etc. and fill with a detergent steriliser. Leave for two hours drain and then refill with water.
  8. Pressure wash the complete building using hot water or a steam cleaner.
  9. Visually check the building.
  10. Disinfect the complete house including all equipment and surrounds using a pressure washer or spray.
Follow this with fumigation using formalin gas where this is permitted with suitable precautions. Alternatively use a disinfectant such as Virkon S. (See Chapter 15) Place a disinfectant foot bath outside the house and use prior to entry.

Do not restock the house until dry. (A minimum of 48 hours). If you have to occupy the house before this then use a space heater to dry out the surfaces. You will see from the above there are three chemicals required for the cleaning process.

First a detergent, which helps remove dirt and soiled material, second a detergent steriliser for cleaning and sterilising the water systems and finally a disinfectant to complete the cleaning process.

In houses where the floors are worn and in particularly farrowing pens it is good practice to brush the floor with lime wash (whitewash) after cleaning and disinfection. Carry out this procedure as follows:

  • Wear goggles and gloves when handling this material since it is very irritant.
  • Mix sufficient hydrated lime with water to produce a consistency of thin salad cream.
  • Cover the farrowing house floor with the whitewash, using a soft household brush.
  • Leave the surface for 48 hours to dry.
  • Do not move the sow into the crate whilst the lime wash is wet. If you have to move the sow in before this do not brush the floor area where the sows udder will make contact.
  • Lime wash can also be used on all concrete floors and can be of value in pens where, for example, greasy pig has become a problem. It is a very cheap disinfectant and its value can be enhanced by adding 30g of phenolic disinfectant to 4.5 litres of lime wash.
Guidelines for fumigation
Using potassium permanganate and formalin

Formaldehyde is a noxious and highly toxic gas and exposure for only a short period can cause respiratory distress and with severe exposure ultimately coma. (Its use is forbidden in some countries).

Whenever fumigation is undertaken, there should be two people available. One in the house and one at the door to provide assistance if required.

  • Wear protective goggles and a dampened face mask - these should be available to both persons.
  • Use rubber gloves.
  • Wet the house before fumigating and seal any openings.
  • Always add formaldehyde to the potassium permanganate. Have the exact quantities to be added ready in separate containers and add slowly.
  • Use high sided metal containers for mixing the compounds. Once the compounds are mixed vacate the house immediately.
  • Ensure no livestock will be exposed to fumes that might escape.
  • If the person in the house gets into difficulty, the person at the door should turn all fans on fully, open all doors and immediately pull the person out.
  • Distribute the metal containers evenly through the house.
  • Add 1000mls formaldehyde (40%) to 400grams of potassium permanganate per 1000m3 of air space.
  • Leave the building shut for 12 hours.
  • Open up and ventilate eight hours before use.
  • Place a notice on the door warning people "Fumigation in process".
  • Oxygenating disinfectants such as Virkon S or Kwikstart sprayed as a fine mist, can be used as an alternate to fumigation with formalin. They are much safer and easier to handle.
Washing hands
Disinfection of hands should always take place after handling livestock, particularly where there has been faeces or urine contact. This is not least for personal hygiene reasons. (See chapter 17 Step 5 - Zoonoses....).

Hands should be washed following meals and after frozen or defrosted meat products have been handled because of the risk of transmission of such diseases as FMD, SVD and CSF.

The importance of washing hands after handling diseased pigs has already been highlighted in the case of scour in the farrowing houses. There is often a bewildering array of disinfectants available, each with attractive claims made as to their effectiveness. To make the best cost effective decision a number of questions should be asked.

Key points to consider when selecting a disinfectant (Fig.2-23)

  • Always use a disinfectant that has been independently proven and has been shown to be effective against a wide range of infections but particularly those that are present on your farm. In many countries there are lists of approved disinfectants. Ask your veterinarian or supplier.
  • Dilution rate - always read carefully the instructions as to use and in particular the amounts to be added to water for general disinfectant purposes. Check also the amounts required for the highly infectious diseases such as transmissible gastro-enteritis, aujeszky's disease and PRRS. From the cost of the concentrated disinfectant work out the cost of diluted chemical. A disinfectant costing £56 per 25 litres but with a dilution rate of 1:300 can be a much better buy than a disinfectant costing £56 per 25 litres and a dilution rate of 1:100.
  • Time to act - there is always a minimum time before the disinfectant has killed micro organisms. Since most disinfectants are used at low temperatures always look at the killing time relative to this.
  • Effectiveness in the presence of organic matter - this is important when using disinfectants on the farm, because invariably under such conditions they are going to come into contact with large amounts of organic matter. Some disinfectants such as chlorine are very quickly neutralised in the present of such materials. Footbaths contain high levels of organic matter due to continual contamination.
  • Penetration - it is very important that the disinfectant has the ability to penetrate organic matter (detergency). In most cases however it is preferable to apply a detergent cleaner prior to the use of the disinfectant for more effective use.
Each group of disinfectants have their own special properties and an understanding of these will help you in your selection.



Detergents
These are cleansing agents which have good wetting powers and the properties of penetrating surfaces. Detergents can either be acid, alkaline or neutral. The neutral ones tend to be those such as soaps and liquids that are mainly used to remove soiled materials. They are often combined with the disinfectant to provide a dual action.

Disinfectants
The ideal disinfectant should be:

  • Active quickly against a wide range of viruses, bacteria and fungi.
  • Safe to handle.
  • Active in the presence of dust or organic matter.
  • Have a long period of activity.
  • Non irritant, non staining, non toxic and non corrosive.
  • Combined with a detergent or have such properties.
  • Capable of use as an aerosol.
  • Safe and effective when used in water systems.
  • Capable of use through pressure washers.
  • Coloured.
There are six classes of chemicals used for disinfection:
  1. Phenols.
  2. Chlorine based compounds.
  3. Iodine based compounds.
  4. Quaternary ammonia substances (QACs).
  5. Aldehydes.
  6. Peroxygen formulations.

1. Phenols
These are organic compounds that may or may not be combined with chlorine. They are usually effective in the present of organic matter but do not normally have a high detergent action. They are not however corrosive to metal but they can cause damage to plastic and rubber compounds. There action is moderately slow. Tar acids may be combined with other organic acids such as acetic and sulphuric acids to increase efficiency (e.g. Antec farm fluid S) to improve their effects against viruses.

Key facts about phenolic based disinfectants

  • They are active in the present of organic matter.
  • Their activity persists for a long period of time.
  • They are ideal for vehicle dips and concrete floors.
  • They have no detergent activity.
  • Their rate of activity is slow two to twelve hours.
  • They can be toxic and damage tissues.
  • They are usually very effective against bacteria but not so good against viruses or spore producing bacteria.
  • They are usually quite cheap.
  • Some phenols such as chlorxylenols contain chlorine which adds properties of quick action.
  • They taint milk and processed meat.
2. Chlorine based compounds
The chlorine based compounds can be considered in two groups. Those without organic compounds such as the hypochlorites which depend on the liberation of chlorine for their disinfection action and those that contain organic substances. Chlorine disinfectants have a very quick action but are very quickly neutralised in the presence of dirt or organic matter.

Key facts about the chlorine based disinfectants

  • They can be very corrosive.
  • They have a very quick action.
  • They are inactivated by organic matter and hard waters.
  • They do not persist for very long periods of time.
  • They have no detergent activity.
  • They are very active against viruses and bacteria.
  • They may cause taint.
  • They may be ozone unfriendly.
  • They are very cheap.
3. Iodine based compounds
This group of disinfectants include substances called iodophors where the iodine is dissolved in a surface active agent and then phosphoric acid is added. Iodine substances are very safe, have low toxicity with almost no smell. When phosphoric acid however is added to the iodophors the disinfectant becomes a little more irritant and corrosive.

Key factors about iodine disinfectants (iodophors)

  • Usually they have a high detergent activity.
  • They are ideal for foot baths.
  • They are brown in colour when very active becoming straw coloured when loosing their activity (used in footbaths for this reason).
  • They are very quick in action.
  • They are very effective against viruses and bacteria.
  • They are moderately active in the present of organic matter.
  • They tend to be more expensive.
>4. Quaternary ammonia compounds (QACs)
These compounds may be used for cleaning and sterilising water systems and equipment and they are very efficient, particularly if the organic matter has been removed. They are not usually suitable for the disinfection of premises on their own because of the large amounts of organic materials present that immediately neutralise them. QACs are not compatible with soaps and they should not be mixed with other detergents. Some are used as antiseptics. They are more active against gram positive organisms.

Key factors about (QACs)

  • They usually have littler or no effect against fungi and bacterial spores.
  • Inactive in the presence of organic matter.
  • Inactivated by soaps and disinfectants.
  • No activity against viruses.
  • Suitable for cleaning water systems and smooth surfaces.
5. Aldehydes
These substances such as formaldehyde, are very toxic but are good disinfectants in aerosol form. There are now alternate products available that are equally effective and much safer to use (e.g. Virkon S).

6. Peroxygen compounds
These are the new broad spectrum disinfectants that are highly active against most micro-organisms. They are based on combinations of peroxyacetic acids or other derivatives, hydrogen peroxide, organic acids and anionic detergents. They are powerful oxygenating agents.

Precautions to be taken when using disinfectants

Always:

  • Follow the manufacturers instructions carefully.
  • Wear gloves and eye protectors when handling the concentrate.
  • Wash concentrate off the skin immediately.
  • Ensure the dilution is correct for the purpose being used.
  • If there is contact with eyes wash immediately with copious amounts of water and seek medical help.
  • Where foot baths are used ensure that these are cleaned and replenished regularly.
  • Store in original container, tightly enclosed.
  • Keep away from children.
What should you use on the farm
  • This would obviously depend on availability but the following should be considered:
  • Foot baths - use an iodine based one.
  • General disinfection of houses - use a phenol or organic acid based one.
  • Water - use a QAC or chlorine based one.
  • Concrete surfaces - use a phenol or organic acid based one.
  • Broken floor surfaces not easily cleaned - use an oil based phenol type.
  • Virus infections - use iodophors or peroxygen complexes (Virkon S). (Formalin fumigation is also effective).
  • Bacterial problems - use iodophors or peroxygen complexes.
  • Hands - use QAC compounds or soaps.
  • Loading ramps - use a government approved disinfectant that is highly active against the major notifiable and transmissible diseases in your country.
  • Aerosols - use formalin, chlorine, iodine or oxidising agents preferably the latter.

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