Hypersensitivity pneumonitis is a fancy way of saying allergic lung inflammation. The condition is not really one illness but a group of illnesses that share the same constellation of signs and symptoms with differing specific allergic causes. Based on the particular route of allergen entry into the body, hypersensitivity pneumonitis has been called by a variety of other names, including farmer's lung, ventilation pneumonitis, bird breeder's lung, and chemical worker's lung. In general, whatever the cause, the condition develops after months to years of strong exposure to the allergen.
Depending on whether allergenic exposure is of short duration or persistent, hypersensitivity pneumonitis may follow either an acute or a chronic course. In the acute (short-duration) variety, symptoms typically arise within a few hours of exposure and generally consist of cough, shortness of breath, and flulike symptoms such as fever, chills, muscle aches, and extreme tiredness that last for only one or two days. Progressive shortness of breath and increasing physical disability, however, characterize the chronic (long-term) variety.
Farmer's lung has been linked to exposure to moldy hay, which contains contaminant bacteria believed to be directly responsible for proyoking the allergic symptoms. In this condition the bacteria operate as allergens rather than as infective germs. In the same way ventilation pneumonitis is associated with bacterial and fungal contamination of the water in humidifiers and air conditioners. Here again the germs act as allergens rather than infection-producing agents. Bird breeder's lung is a potential hazard for those raising pigeons, parakeets, chickens, and turkeys. The problem is believed to result from breathing in the dried, powdery fecal material deposited by the birds. And in chemical worker's lung, the symptoms have been tied to inhalation of isocyanates, which are present in polyurethane foam, varnishes, and lacquers.
In most cases, hypersensitivity pneumonitis is a relatively mild illness. When exposure to the provocative allergen is short-lived, the chances for complete recovery are generally excellent. On the other hand, a history of repeated acute episodes presages a worse prognosis. The outcome is also poorer when the hypersensitivity pneumonitis is severe and long-term enough to cause persistently abnormal chest X-ray findings and lung function studies. Somewhat surprisingly, there is a tendency in chronic cases for the severity of symptoms to decrease over time.
The treatment of choice for hypersensitivity pneumonitis, as for most allergic disorders, is avoidance of the allergen. However, as many as 60 percent of farmers and an even greater percentage of bird breeders with the condition are financially unable to give up their work. At the very least these individuals must avoid baling or storing wet hay and should use filter masks or respirators whenever they are exposed. Two choices of filter masks include the disposable 3M model 8710 and the reusable model 7200. Storage driers to reduce moisture buildup and spraying with propionic acid are other effective methods of reducing the bacterial contamination responsible for the problem. Finally, short courses of antiinflammatory steroids such as prednisone may also be used to break the ongoing cycle.
Persons suffering with ventilation pneumonitis would do well to avoid standing water in air-conditioning and humidification units and to make certain that local reservoirs are properly treated to suppress bacterial overgrowth. Finally, chemical workers can reduce their overall exposure by not handling dusty materials within small, closed spaces and ensuring that all standards for proper ventilation are being adhered to in the workplace.
