Common complaints: Bird fancier's lung

BIRD fancier's lung is an allergic lung disease which is quite distinct from asthma. It is due to sensitivity developing to inhaled dust from the feathers and droppings of birds such as budgerigars, parrots and

pigeons. Bird fancier's lung is only one of a group of conditions known as hypersensitivity pneumonitis, which are due to inhalation of dusts composed of organic materials.

Probably the most common of these is farmer's lung, due to inhalation of mouldy hay; but the occupations in which dust inhalation may cause illness include mushroom growing, cheese-washing, coffee growing, fishmeal manufacturing and the fur trade. Even office workers are not exempt. The condition of humidifier fever or air-conditioner lung is due to inhalation of air contaminated by moulds growing in the humidifier water tanks. In each of these occupational or recreational settings only a small fraction of those exposed to the dust become ill, and prolonged exposure to large amounts seems to be necessary.

Once sensitivity to the dust has developed, symptoms occur whenever it is inhaled - with a time-lag of around four hours. The most obvious features are shortness of breath and coughing, but a raised temperature and attacks of shivering may suggest an infectious illness. Wheezing is unusual - and, indeed, asthmatics rarely develop this type of sensitivity, being unable to tolerate the amount of dust necessary for the condition to become established. In the early stages all the symptoms disappear within a few hours if the victim stops breathing the dust.

Recognition of these disorders should be obvious enough; people exposed to dust at their workplace are typically free of any problems with their breathing at weekends. The connection between the illness and dust exposure may not be made, however, especially by bird fanciers and by small farmers - two categories likely to come into contact with the trigger dust every day. Their doctors may be slow to make the connection, since the symptoms will rarely be present on the day that the sufferer stays away from work to attend the surgery. If the diagnosis is missed the disease become progressive, causing loss of weight, fatigue and increasing difficulty in breathing which may eventually be crippling.

X-rays of the chest, and lung function tests, may be normal at first but, in people with chronic disease, they show that the lungs have become stiff and fibrotic. Blood tests will show that antibodies have developed against the dust responsible. A similar condition - cryptogenic alveolitis - does sometimes occur with no dust trigger.

Treatment of hypersensitivity pneumonitis is straightforward if further exposure to the dust can be prevented. Otherwise, control of dust levels will help, and masks are available for farm workers. In some occupational dust disorders the key to control is to prevent moulds from growing on the material people are working with.

Drug treatment with corticosteroids will relieve the symptoms, and this may sometimes be useful; but avoidance of the dust is essential if the disease is not to progress. This collection of conditions with bizarre names, often still poorly understood, requires the oldest of medical skills - careful interrogation. 'Listen to the patient,' said the famous physician Sir William Osler to his students. 'He is telling you the diagnosis.'