Don’t rely on disinfectant
Disinfectant use is essential but not a panacea for all ills or a magic cure on its own. Cleanness of surfaces to be disinfected and application methods employed rather than the actual chemical disinfectant used will usually determine whether a disease free house is achieved.
Dirt and organic matter such as dried and hardened faeces, mucous, feathers and spilt feed will inhibit disinfectant action because there must be direct contact between the biocide and the pathogen.
Modern disinfectants are put through stringent laboratory tests such as the Kelsey Sykes Test that simulates real working conditions in the poultry house. These assess biocidal activity in the face of repeated ‘challenge’ by organic matter and effect of hard water caused by high levels of calcium or magnesium salts.
Many chemicals including strong acids and bases, chlorine generators, phenols, aldehydes, quaternary ammonium compounds, iodophors and peroxygen compounds possess disinfectant action. Some such as iodine based compounds have a long history of use but limited action and a relatively narrow range of kill. Others like formaldehyde though widely used in the past are now largely avoided for reasons of safety to both birds and poultry workers.
Modern disinfectants are potent biocides with broad-spectrum activity and a long contact time in which to kill pathogenic microbes. For instance, peroxygen compounds that disrupt and destroy microbes through oxidation reactions will destroy most types of pathogenic microbe. These include bacteria (e.g. Salmonella typhimurium and Escherichia coli) viruses (e.g. avian influenza and infectious bronchitis) and fungi (e.g. Aspergillus fumigatus and Canida albicans). Contact time is increased by the addition of a surfactant. Surfactants are surface-active chemicals that lower the surface tension of the diluted disinfectant mixture to increase penetration and spreading power of water-based biocides.
Facts about fogging
Power washing with detergent will remove dirt and organic matter from accessible surfaces and leave them clean and ready for disinfectant action by ‘wet’ spraying. But poultry houses are typically riddled with ‘nooks and crannies’ – fan shafts, ducts and other areas inaccessible to standard cleaning and disinfectant spray programmes. These out of the way areas can only be ‘covered’ by space spraying using droplets small enough to penetrate into the smallest crack and corner. ‘Dry’ application of disinfectant by thermal (hot) fogging is the only application method that can realistically achieve this goal.
Thermal foggers operate by vapourising the liquid disinfectant mixture that subsequently issues through the fogging pipe as mixture of hot gases. On contact with cold air it condenses into a mass of tiny droplets which form the fog.
Benefits of hot fogging disinfectant arise from two basic laws of physics that relate droplet number to droplet size, and suspension time with droplet size:
The number of droplets generated from a given volume of spray liquid is inversely related to the cube of the droplet diameter (Table 1). .
The smaller its size (diameter), and therefore it’s mass, the longer a droplet will be suspended in the air (Table 2).
Hot foggers produce droplets of 5-25μ in diameter. The larger droplets cover the walls, floor and ceilings to provide residual disinfection. The smaller droplets stay suspended in the air for space disinfection, thus acting against airborne spores and dust-borne infections. Disinfectants with a relatively high vapour pressure perform best during hot fogging, although fog-enhancing chemicals are available to improve performance of a wide range of disinfectants. Disinfection by hot fogging may be achieved at very low volume application rates of 20 litres/1000 cubic metres.
Fogging may also be used to control insect pests and pathogenic microbes in bagged/sacked feed storage areas. Ideally it should be carried out when the store is empty. But it can also be used as an emergency measure when the store is full, provided the biocide is cleared for such use and the bags/sacks are stacked with ample space.
Thermal foggers can be operated in the hand-carried mode, in a stand-alone mode within the building, or from outside by fogging through ports in the walls. If hand-carried the operator should start at the far end of the building and retreat carefully to the exit as he/she fogs. Full protective clothing including a respirator must be worn.