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About Aerial Disinfection

by 5m Editor
27 April 2001, at 12:00am

Further to recent news reports about the possible benefits of aerial disinfection we have conducted some investigations and Antec International have provided the following article prepared by A. E. J. Waddilove MA VetMB, MRCVS. Aerial disinfection is an important part of the Biosecurity Programme on any farm and can have a major part to play in preventing or controlling disease. Essentially Aerial disinfection is the process of disinfecting suspended particles in the air for a period of time. This article refers in the main to pigs but the could be similarly applied to other animals.

Why should we do it?

Basically there are two main reasons:

Firstly:
As part of a terminal disinfection programme between batches or when depopulating all or part of a farm. In this role it is usually done after the main disinfection is completed, and after moveable items and bedding have been returned. The purpose is threefold:

  1. To control any contamination that might have been re-introduced with these articles.
  2. To disinfect areas which are inaccessible to normal procedures, either by virtue of their position or proximity to electrical supply or similar.
  3. To help reduce any dust etc. which has been created.
It should be stressed that this is part of the complete programme and does not replace the normal disinfection in that programme.

Secondly:
While the building is still populated with pigs. Here there are 3 main reasons for doing it:

  1. To reduce the airborne spread of pathogens and other micro-organisms.
  2. To reduce levels of dust.
  3. And hence to reduce the levels of airborne challenge to the pigs by endotoxins (toxins produced by certain bacteria which can be carried on dust - they have significant effects on productivity and disease).

In this role aerial disinfection can be carried out daily or even more frequently, and can be highly effective.

The importance of aerial disinfection while pigs are in the building can be seen from a keynote paper at IPVS 1998 by Poul Baekbo (Proc. IPVS 1998, 1, 135). He concludes that dust and endotoxins contribute to the development of respiratory disease in pigs and allowed a smaller dose of pathogen than normal to cause clinical pneumonia. Thus if we reduce pathogens, dust and endotoxins in the air by aerial disinfection we can expect to help control pneumonia - especially in herds with existing problems.

How can we achieve Aerial Disinfection?

There are 4 main ways of suspending disinfectant particles in the air of a pig building.
  1. By spraying - using a knapsack sprayer or pressure washer. This produces relatively large particles, which have a higher wetting capacity, but stay in the air for less time.
  2. By misting - (This is also known as cold fogging.) Done by using a mechanical mister (e.g. those produced by Stihl & Curtis Dyna-Fog Limited). This produces smaller particles that have increased penetration and uniformity.
  3. By fumigation - the combination of 2 or more chemicals producing a vaporised form of the disinfectant. This is really only used with Formaldehyde and related products.
  4. By thermal fogging - similar to misting but involving heating of the disinfectant to produce a fine vapour. The small particle gives the best penetration and suspension.

What Disinfectants can be used?

Various products can be used for aerial disinfection:

  • Formaldehyde - used for fumigation and theoretically other methods. Cheap and quite effective, but carries major health risks for animals and operatives. (In humans these can include skin and mucosal irritation, respiratory problems, asthma, sensitisation and possible carcinogenic effects). Importantly residues on walls can be released several days later. Effects can be cumulative. In view of modern concerns for health and safety the use of this chemical should be strongly questioned. Obviously it cannot be used in the presence of pigs.
  • Glutaraldehyde - very similar to formaldehyde and burdened with the same risks. One extra danger is the absence of an unpleasant smell.
  • Glutaraldehyde-QAC Ammonium mixtures - these have a lower efficacy than Glutaraldehyde but still have significant health risks. Not efficient enough or safe enough for common use.
  • Virkon S - a powdered peroxygen which is made up into solution. Has proven high levels of activity against a wide range of common pig pathogens. It is safe in use for both operators and pigs. As a result it can be used in terminal disinfection programmes or while pigs are still in the buildings.

UK MAFF Approved Efficacy Table

The table below show the results of efficacy tests conducted by MAFF. As the table indicates Virkon S provides the highest efficacy level (effectiveness) of the products tested.

Product / Disease Foot & Mouth Disease Swine Vesicular Disease
Formaldehyde 1:9 1:9
Glutaraldehyde / QAC 1:80 Not Approved
Virkon S 1:1300 1:200

Which is the best method?

This is really a question of horses for courses. The different methods all have their ideal applications.
  • Spraying is ideal for small rooms or buildings, perhaps especially where dust is more of a problem. It can be done in the presence of pigs.
  • Misting is better for larger buildings and tall buildings. The lower particle size means the disinfectant is suspended for longer. Again it is safe for use while pigs are in the building.
  • Fumigation can only be used on an empty building. It provides good penetration of disinfectant for a lower price. The major disadvantage is the significant health hazard of the products used. (e.g. Formaldehyde).
  • Thermal fogging is ideal for very large houses or moving around larger operations. The level of disinfection spread is good, but the noise of the machine can be disturbing to pigs. Interestingly this method is commonly used in the poultry industry - and how often has this set the standards for pigs?

Further Information

The following feature articles are also available on this topics:

Two Methods of aerial disinfection

Additional information is also available on the DAHS web site

Written by A. E. J. WADDILOVE MA VetMB, MRCVS - 2001


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