Blight is a common disease for many plants, including pansies, and is caused by fungus. Rainy weather contributes to this disease, although it can also occur if the atmosphere is simply very humid. Pansies with this disease may look wilted and have patches of grey or brown on their foliage and/or blooms. If the disease is left untreated, the flowers will eventually die. Curing blight on pansies is a several step process--good results depend on how early you catch the disease before it spreads.
Put on rubber gloves to keep your hands clean. Unless your garden gloves are washable, you shouldn't wear your regular gardening gloves while working with diseased plants, as you may later inadvertently contaminate healthy plants.
Pick off and discard all diseased flowers and leaves (those showing wilting or discoloration). If the entire plant appears to be infected, remove it and discard the plant. Cornell University's Plant Disease Diagnostic Clinic suggests doing this when plants are not wet, as there is a higher danger of cross-contamination when plants are wet. Also, dispose of diseased plant material in a paper bag so you can easily discard it with your household trash or burn the plants.
Remove organic debris from around the pansies. This includes leaves and mulches that could harbor disease spores. In addition, if your flower bed is very crowded, you should thin out the plants to provide more air flow.
Use a fungicide for flowering plants. You may need to purchase or borrow a garden sprayer to apply the fungicide. Follow directions carefully and apply it in the morning, and not in the heat of the afternoon sunlight (or you could accidentally burn the plants with the product).
Water pansies less frequently. The University of Georgia's Center for Urban Agriculture suggests letting the plants dry out in between watering, as well as removing dead lower leaves (especially those on or close to the ground).