This reaction is typical of Farmer's Lung. Certain types of white blood cells move into the lungs to attack the antigens. Then, other types of white blood cells move into the lungs, releasing chemicals and poisons that increase blood flow and kill lung tissue close to the antigens. This response causes swelling, inflammation and damage to lung tissue, resulting in noticeable breathing problems. There is little information on the exact number of people with Farmer's Lung in Canada.
Studies show that incidence varies from place to place.
The disease seems to occur in about 2 to 10 percent of farm workers, depending on the region. In some areas, blood tests have shown that 20 to 40 percent of farm workers have antibodies that react with antigens responsible for Farmer's Lung. This test indicates that people have had at least an initial exposure to moldy dust. The disease is most common in regions with wet weather at harvest time. Farmer's Lung is also more common on dairy farms, especially those not equipped with automated equipment for handling hay or feed.