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Diseases due to work in hay dust have long been known in Iceland and the first written records of them appear in the beginning of the 17th century. At the end of the 18th century, a district doctor alleges that they cause many deaths in the country. In the latter part of the 20th century, research was started to investigate the causes and nature of hay diseases in Iceland. Studies of allergens showed high levels of storage mites in hay. Highest levels were of Tarsonemus sp., Acarus farris and Lepidoglyphus destructor. A several micro-fungi were also found, most commonly Rhizopus sp., Penicillium sp. and Aspergillus sp. Micropolyspora faeni was also found in all hay samples.

A study was done on people aged 6-50 years in two districts in Iceland. In one district farmers used almost exclusively dry hay and in the other they used 80-90% silage. There was no difference in IgE-mediated allergy between the provinces, but most had positive skin tests for L. destructor and cattle.  Those with symptoms connected with hay dust most often reported nasal symptoms (79%), eye symptoms (63%), cough (41%), dyspnea (32%) and fever (21%). Those who had positive skin reaction complained most often of nose and eye symptoms.

A study was also conducted on subjects aged 16-87 years from the same regions investigating precipitin tests for M. faeni, Thermoactinomyces vulgaris and Aspergillus fumigatus. Pulmonary symptoms and lung function were also investigated. Precipitin tests were almost exclusively positive for M. faeni, and 5 individuals were positive for A. fumigatus and none for T. vulgaris. The precipitin tests were significantly more often positive in those working almost exclusively with dry hay (72.9% vs. 23.9%). They had also more commonly obstructive pulmonary disease (FEV1/FVC%<70: 24.8% vs. 9.5%) as well as dyspnea when walking on level ground. There was a positive correlation between positive precipitin tests for M. faeni and dyspnea walking on level ground.

The sensitivity and specificity of positive precipitin tests for M. faeni were investigated to detect farmer’s lung. The sensitivity was 82% and specificity was only 49%. A survey of emphysema in patients in the only Pulmonary Clinic in the country showed that farmers had more often emphysema than the rest of the country population, and 58% of farmers with emphysema had smoked compared to 94% of other emphysema patients.