Water-sensitive paper is a rigid paper (card) with a specially coated, yellow surface which will be stained dark blue by aqueous droplets impinging on it. It has been developed for the quick evaluation of spotting or for field use of low volume (LV) sprays. For droplet assessment aqueous sprays no longer need the addition of dye.
It helps to visualize droplet distributions, droplet densities and spotting quality.
Handling, Limitations and Storage
Water Sensitive Paper packed in its original high-quality sealed alubags can be stored for 10 years and more, provided the sealing remains undamaged. Water-sensitive papers must be stored before and after spray exposure under dry conditions in airtight bags or boxes. Exposed water-sensitive papers can also be protected with a colorless, thin adhesive foil. Avoid air pockets when applying the foil. Aerosol sprays of colorless, synthetic resin can also be used. The pH value of the resin must be in the range of 4.5 to 6.0. Observe instructions for use when spraying with an aerosol can.
Analysis and Evaluation Check the droplet pattern
For a quick estimate compare the exposed droplets with a known standard or examine the droplets either using a hand lens or an automatic image analyzer. Droplet counting by hand lens on WSP is limited to a maximum of around 200 droplets per cm2. For higher droplet densities use automatic image analyzer. Accurate drop size and pattern measurements with commercial imaging software can only be made if the drop density is low enough for the majority of droplets not to overlap each other.
WSP is produced under careful and rigid process control. To maintain this high quality standard, follow the instruction below.
Use always gloves (polyethylene or rubber) when handling the WSP to avoid any staining and contamination of the water-sensitive surface.
The WSP should be processed under clean conditions only. Dust particles may cause local alterations in the wetting characteristics of the slide surface, which result in depositing failures.
Since the yellow surface is sensitive, direct contact and any touch of the spotted slide surface must be avoided.
The WSP cannot be used at a relative humidity of more than 80 %. Although it turns light blue at a relative humidity of 80 % the stains produced by droplets still show sufficient contrast to allow visual control beyond this limit.
If you want to produce high-density arrays with a spot size smaller than 100 µm you should adjust the relative humidity to approximately 40 - 50 %. Pure water stains the water-sensitive paper in drop sizes as small as 50 μm even at temperatures of T=50°C and relative humidity of 20%.
WSP is not recommended for use at temperatures below 10 °C.
After spotting the WSP must be protected with a colourless, thin adhesive foil (e.g. scotch tape). Avoid air pockets while adhering the tape.
Monitoring Vaccine Spray Distribution Using Water-Sensitive Paper
Water-sensitive paper strips are widely used in agronomy to monitor the distribution of herbicide/pesticide spray in fields. The water-sensitive paper is a rigid paper with a special coated surface designed to stain blue when the paper is contacted with water droplets. The paper can be used to check the vaccine spray distribution within a caged flock. The droplet density at the target areas can be evaluated. Also, a rough visual estimate of the droplet size and the uniformity of the spray droplets can be evaluated. The strips need to be handled carefully after removing them from their package. Plastic gloves are helpful to prevent the moisture on fingertips from leaving marks upon the paper. Houses with high relative humidity can also affect the paper by diffusely changing the paper strips blue. The strips of paper should be retrieved as soon as the spray has dried and evaluated. The strips can be stored in a clear plastic folder to be examined later.
The procedure is to place strips of water-sensitive paper within empty cages at selected locations within the house. The paper can be woven between the wires of hung from the top of the cage. The selection of cages to be used during the evaluation can be random or according to a predesigned pattern. The important point is that cages at all levels (upper, middle, bottom) and positions within a cage row (front, middle, back) be evaluated. It is also advisable that the person actually spraying the vaccine not be aware of the exact position of the test cages to prevent an unintentional bias in the spray technique.
The examination of the paper strips can reveal if large sections of the cage row are being missed. The use of sprayers having multiple spray nozzles can be evaluated to establish if the spray nozzles are properly positioned at each cage level. The target area of a spray should be head level to the bird. It is common to find sprays that are directed too low and are spraying the legs and feet of the birds. Sprayers with a single want (back pack type sprayers) are easier to apply unevenly because the wand is hand held and the applicator may not consistently apply the spray in the same way.
Another common problem encountered is that the total numbers of vaccine doses are unevenly applied in the house. The last cage row sprayed is often the area shorted of vaccine. Simply adding more water to the remaining vaccine solution in order to finish the last cage row only dilutes the vaccine. And, in extreme cases, might dilute the vaccine below an immunizing dose. A remedy for this is to divide the total doses of vaccine and mix only the vaccine required for half of the house, and mix a fresh solution with the other half of the vaccine to finish the house. This approach would avoid large mistakes in vaccine distribution. There is also the advantage in keeping the vaccine solution fresh and high titered.
House lights should be dimmed to prevent the birds from avoiding the spray. It is not necessary to make the house completely dark, but dim the lights enough so that the birds stay evenly distributed within the cages. Birds under dim light conditions seem to be curious of the sound made by the sprayer and will hold their heads high and pointed toward the spray.
Doubling the spray volume to allow two passages of the spray over the flock would provide the most complete coverage. This method is not popular because of the extra time and labor involved, but might be considered when complete coverage is vital (revaccination in the fact of an outbreak with ILT vaccine).
High quality (distilled, bottled or known good quality) water should be used for mixing vaccine solution. Good quality water is particularly important for spray vaccination because dried skimmed milk cannot be used to protect the vaccine as is often used for drinking water vaccination. The water used should be free of chlorine or other substances, which might adversely affect the vaccine. The reconstituted vaccine solution should be used immediately within two hours. The vaccine titers of liable vaccines such as bronchitis and AE can deteriorate quickly after reconstitution in water.
In conclusion, spray administration of vaccine is not an exact science and it is often the proficiency and experience of the vaccinator and sprayer function which most determines success. Water-sensitive paper appears to be a useful tool to monitor the spray vaccination protocol.