Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. Downloaded from

Brit. J. industr. Med., I965, 23, i6

Farmer's Lung: A Review J. WATKINS-PITCHFORD Chief Medical Officer, Ministry of Pensions and National Insurance

Pulmonary disability among agricultural workers traced the responsible organism to thermophilic handling mouldy hay has been known for genera- actinomycetes which developed in damp hay as it tions and it seems probable that Ramazzini's became overheated due to moulding. Characteristic description in 17I3 of the Diseases of Sifters and precipitin reactions were obtained only from the Measurers of Grain included the condition now serum of subjects exposed to mouldy hay and from known as farmer's lung. However, it was first a high percentage of patients with the clinical described as a clinical entity by Campbell in 1932 features of farmer's lung. and by Fawcitt in I936. Both these authors col- lected their material from the North-west of Incidence England, an area of high rainfall, but it exists in other areas as well. In 1953 Fuller reported on 32 cases from the Devonshire area and Williams and The true incidence of farmer's lung must be Mulhall (I956) collected io cases in Radnor and largely conjectural. However, it is certainly not a Breconshire. In I96I Staines and Forman reported- rare condition in some parts of the country. A con- the results of a survey conducted on behalf of the sultant dealing with a Welsh rural population of copyright. College of General Practitioners; 444 cases had been 9o,ooo saw I95 cases in eight years. There is a reported to them but the criteria of diagnosis were marked regional variation, and the survey carried out defined broadly, and some of these cases may have by Staines and Forman on behalf of the College of been due to other pulmonary disabilities. This General Practitioners disclosed an incidence of IO-5 work demonstrated the difficulty of diagnosing the per ioo,ooo general population and I93 I per condition and also a correlation between the I00,000 farming population in Wales while the incidence of the disease and rainfall, both geo- figures for East Anglia were I -2 and I1-5 respectively. http://oem.bmj.com/ graphical and seasonal. Cases have also been The authors of this report put forward a 'specula- reported from Ireland, Iceland, Switzerland, Nor- tive incidence' in the British Isles of about I,000 way, Sweden, Finland, and New Zealand. In the cases a year. United States Dickie and Rankin (I958) examined Cases occur at any time of the year, with the 39 patients with farmer's lung and obtained lung exception of a few weeks in midsummer, but there biopsies in eight of them. Rankin, Jaeschke, Callies is a noticeable preponderance of cases diagnosed in and Dickie (I962) published a pathological and the early weeks of the year when stored hay is being physiological study on 34 additional subjects. used. A study of meteorological data shows an on September 25, 2021 by guest. Protected The relation of the disease to the inhalation of increase of cases following a summer of heavy rain- mouldy vegetable matter has never been questioned fall when hay has presumably been stored with too but the view that it was a true pulmonary mycosis high a moisture content leading to overheating, was challenged by Duncan in I945 and subse- moulding, and suitable conditions for the growth of quently by Fuller in 1958 and I962. In I962 Pepys, the incriminated actinomycetes. The evidence is Riddell, Citron, and Clayton, in a detailed report conflicting on whether the incidence of the disease dealing with the immunological investigations into is changing. It is reasonable to suppose that modem the agent in mouldy hay responsible for farmer's combine harvesters and drying facilities will do lung, demonstrated antigens in mouldy hay which much to reduce the risk as far as grain crops are seemed to be responsible for the disease, and in a concemed. On the other hand, it has been sug- further report the following year Pepys, Jenkins, gested that the practice of baling hay in the fields Festenstein, Gregory, Lacey, and Skinner (1963) may have the opposite effect. The ratio of males to females among reported Received for publication August i8, I965. cases is about 20:i, but this probably reflects the x6 Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. Downloaded from

Farmer's Lung I7 preponderance of males over females in the dustier illness may be short and a rapid and permanent agricultural jobs. recovery made. It is probable that the majority of The majority of cases so far reported have arisen patients with these acute symptoms never seek within the agricultural industry and ancillary occu- medical help, and, among those who do, the transi- pations. However, it appears probable that the tory nature of the disability tends to result in the disease can be caused by the inhalation of dust from correct diagnosis being overlooked. a variety of organic substances provided they have If the acute attack is severe, or if exposure to the been stored for a sufficient time under conditions antigen is continued, the illness may merge into the favourable to the development of the thermophilic subacute stage characterized by severe dyspnoea and actinomycetes or similar organisms. The condition which may then become productive. Slight known as bagassosis, first recognized in Louisiana haemoptysis has been reported. may be in 1937 and described by Hunter and Perry in I946 present, and fine crepitations are audible over the following an outbreak in England, presents a clinical lung bases with weak breath sounds. The radio- picture very similar to that of farmer's lung. logical appearances may show a fine mottling, Bagasse is the residue of sugar cane after the sugar usually more marked in the lower lung fields. Head- has been extracted. The residue is baled and used ache, loss of appetite, and evening pyrexia are for making insulating board for the building trade. common, but the symptom that drives the patient The outbreak described by Hunter and Perry to seek medical advice is usually the dyspnoea which followed the introduction of a shredding machine to may be out of all proportion to the clinical signs. break up the bales. Before the introduction of this Provided there is no further exposure to the antigen, machine the bales were opened under water and so this subacute phase may last for up to six months gave rise to no dust and no pulmonary disability. A and, although there may be some residual pul- larger outbreak occurred more recently in a newly monary dysfunction, complete recovery may be opened paper mill in Puerto Rico (Buechner, I96I). expected in the majority of cases. However, each Pulmonary disability following the inhalation of attack requires a longer period of recovery until the grain dust has already been mentioned, and similar chronic third stage is reached. From this stage no conditions have been described in workers engaged recovery is to be expected since it is characterized copyright. in the now obsolete process of splitting the dried by a fine interstitial fibrosis frequently accompanied pods of the paprika plant and in the use of a size by a honeycomb type of bronchiectasis. derived from tamarind seed in the textile industry (Murray, Dingwall-Fordyce, and Lane, I957). The Radiological Appearances serology of these conditions has not as yet been explored and their relation to farmer's lung is un-

Radiology can provide useful supporting but not http://oem.bmj.com/ certain. It has been suggested that the disease conclusive evidence. In the subacute stage many known as 'broken wind' in horses is of the same cases of farmer's lung show a mottling-generally nature as farmer's lung. This condition appears to fine-most prominent in the middle and lower lung be more common during the winter months and is fields. This mottling tends to clear as the reaction confined to stabled horses, but the post-mortem subsides but there may be no radiological change at findings suggest hypertrophic emphysema without all. A similar picture may be seen in pulmonary an interstitial fibrosis. However, 'fog fever' in cattle , miliary tuberculosis, and some pneumo- is probably identical with farmer's lung. conioses. In the more chronic stages the radio- on September 25, 2021 by guest. Protected graphic findings are similar to those seen in inter- Symptoms and Signs stitial fibrosis of whatever aetiology. Acute, subacute, and chronic stages of the disease have been distinguished, but one stage may merge Pathology imperceptibly into the next. In about half the cases there is no clearly defined acute stage and the disease The histological appearance of the lung after a develops insidiously following repeated exposure to recent attack is essentially of sarcoid-like granulo- the dust of mouldy vegetable matter (Pepys and mata with epithelioid cells, macrophages, multi- Jenkins, I965). Acute attacks begin some hours nucleated giant cells, and occasional eosinophils. after exposure and are characterized by distressing There is also a diffuse mononuclear infiltration. , fever, malaise, and cough which The more chronic cases show a diffuse interstitial is usually unproductive. Moist sounds may be heard fibrosis frequently associated with cystic honey- in the chest, but there may be no radiological signs combing. The fibrosis has no characteristics to at this stage. If there is no further exposure the distinguish it from any other interstitial fibrosis. Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. Downloaded from

I8iJ. Watkins-Pitchford Diagnosis conditions as in farmer's lung the main feature is the replacement of normal lung by granulation The farming community is subject to the various tissue and subsequently by fibrosis, thus reducing pulmonary diseases that occur in the general com- the distensibility of the lung and the area of the munity. Pulmonary disability in a farmer is not alveolar capillary membrane available for the ex- necessarily farmer's lung. In the early stages of the change of gas. This reduction in functional area of disease it may be possible to diagnose the condition the membrane is associated with a reduction in the in some cases with tolerable certainty on the history diffusing capacity of the lungs, especially the and clinical examination alone, but it must be diffusing capacity of the alveolar capillary mem- remembered that the condition is most likely to be brane, and the condition is sometimes referred to as met in the early months of the year, a time when 'alveolar capillary block'. Pulmonary function acute respiratory infections are most common. A studies demonstrating a reduction in the diffusing short-lived episode of fever, and cough with capacity of the alveolar capillary membrane in inter- dyspnoea out of all proportion to the clinical signs, stitial pulmonary disease such as farmer's lung are coming on about six hours after known exposure to distinguishable from those obtained in cases of the dust of mouldy hay or similar mouldy vegetable obstructive lung disease. Obstructive lung disease matter, possibly with a history of previous similar is characterized by a persistent rise in airways episodes that can be related to similar exposures, is resistance due to a narrowing of the lung airways, highly suggestive of farmer's lung. This clear-cut, their premature collapse on expiration, and also typical picture is seldom seen in practice as the maldistribution of ventilation. There is, of course, sufferer frequently does not seek medical advice and no reason why a reduction in the diffusing capacity recovers within a few days. The subacute and of the alveolar capillary membrane should not exist chronic stages of the disease are likely to present together with obstructive lung disease, and a farmer much greater difficulty, particularly when the with chronic demonstrating obstructive sufferer is a middle-aged person with a pulmonary lung disease may also have a superimposed inter- disability which may be due to farmer's lung, stitial pulmonary fibrosis due to farmer's lung with chronic bronchitis, or both conditions simul- a consequent reduction in the diffusing capacity ofcopyright. taneously. Farmer's lung may develop insidiously, the alveolar capillary membrane. Indeed it is this and even the history of previous typical attacks combination that is likely to cause the most difficulty following exposure to mouldy hay may be absent. in diagnosis. In these cases, which may well prove very common, a clinical examination alone is unlikely to prove Inhalation Tests Williams (I963) described sufficient to establish the diagnosis. Fortunately inhalation tests for the diagnosis of farmer's lung. there are aids to diagnosis available. Aerosols of mouldy hay extracts provoked reactions http://oem.bmj.com/ in I2 out of IS patients allegedly suffering from Skin Tests Skin tests with extracts of mouldy farmer's lung, while no reaction occurred in 20 hay are of little diagnostic value. No immediate controls. Reactions were characterized by a delay hypersensitivity reaction occurs except in patients of several hours when typical acute attacks of who have a superimposed allergic . Most farmer's lung occurred with a fall in pulmonary hay extracts give rise to a non-specific irritant effect diffusing capacity but no evidence of airways and are therefore unsuitable for skin testing. How- obstruction reversible by isoprenaline. Similarly ever, skin tests with other extracts may have a place designed tests on 38 allergic asthmatics using appro- on September 25, 2021 by guest. Protected in the differential diagnosis of conditions such as priate antigens resulted in the immediate onset of asthma and pulmonary aspergillosis which might be bronchospasm. The inhalation of extracts of clean confused with farmer's lung. hay or extracts of the fungi of mouldy hay caused no reactions, and it was concluded that the respon- Lung Function Tests The assessment of lung sible antigen was neither in the hay itself nor the function is of major importance in the diagnosis of contaminating fungi and bacteria but was a product the disease. Cases of farmer's lung exhibit the of the interaction of the two. Subsequent to this changes in lung function that are associated with investigation it was shown by Pepys et al. (I963), as interstitial pulmonary disease. These changes also has previously been mentioned, that the source of occur in pulmonary sarcoidosis, and the responsible antigen was certain thermophilic other granulomatous conditions of the lungs, the actinomycetes, and inhalation tests with the most Hamman-Rich syndrome, cystic fibrosis, alveolar important of these, Thermopolyspora polyspora, have proteinosis, and alveolar calcification, and they may produced farmer's lung reactions in affected also be found in asbestosis and bagassosis. In these subjects. Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. Downloaded from

Farmer's Lung I9 Corticosteroid therapy suppressed the reaction to pulmonary disability will require further investiga- the inhalation of the antigen in susceptible subjects tion. and this observation may be of value in the manage- It will be apparent that, although a negative ment of the disease. precipitin reaction does not support a diagnosis of Deliberate challenge with antigens to which the farmer's lung, it does not absolutely exclude it, and subject may be susceptible is not without danger a positive reaction, though strongly suggestive, is and should be attempted with caution in the elderly not by itself conclusive evidence. or respiratory cripple. Differential Diagnosis Serological Tests The demonstration of precipitins against extracts of mouldy hay in the Chronic Bronchitis and Emphysema The sera of patients suffering from farmer's lung by typical physiological, radiological, and pathological Pepys et al. (I962) has not only provided valuable features of farmer's lung are absent in these condi- supporting evidence for the diagnosis of the disease tions. The usual auscultatory findings are rhonchi but has also made it possible to identify the source which are not typical of farmer's lung. Precipitation of the antigens responsible. However, the authors tests with sera will, in the majority of cases, show point out that the investigations are at an early no reaction to the prepared farmer's lung antigens, stage, and refinements of technique are still being and'inhalation tests will not show a reaction delayed developed. by a few hours and culminating in an acute farmer's The method now being used is the immuno- lung episode with a fall in pulmonary diffusing electrophoretic test in which the antigens of the test capacity. Furthermore, the history of the illness extracts are diffused throughout the agar-gel by will not suggest any special relation to exposure to electrophoresis and are then allowed to react with mouldy hay. the test sera. This test has shown a characteristic It has previously been pointed out that there is no precipitation pattern with the sera of most of the reason why the disease of farmer's lung should not typical cases of farmer's lung. The main source of be superimposed on a case of chronic bronchitis, the antigens responsible has been shown to be and it is these patients who are likely to cause most copyright. Thermopolyspora polyspora and to a lesser degree difficulty. Microspora vulgaris. Certain other actinomycetes and streptomycetes may occasionally be involved, Asthma Asthma is a common condition in the but they have not as yet been identified with general population and, although a farmer may well certainty. A characteristic precipitin pattern is develop this as a result of occupational exposure to obtained with about 90% of sera from cases believed an allergen to which he is hypersensitive, there to be of farmer's lung. The remaining io% may be should be no difficulty in distinguishing uncom- http://oem.bmj.com/ explained either as examples of an incorrect initial plicated asthma from farmer's lung since the two diagnosis or more probably as due to the responsible disorders differ strikingly. antigen being one of the actinomycetes or strepto- An attack of asthma develops within minutes of mycetes awaiting identification. It is already exposure to the offending substance. An attack of evident that the final figure of positive reactions will farmer's lung develops some hours after handling be above 90% when the tests are performed with an mouldy hay. Exposure to mouldy hay followed by adequate series of antigens. an immediate hypersensitivity reaction suggests Sera from patients who have been exposed to asthma since this type of allergic response is un- on September 25, 2021 by guest. Protected mouldy hay and have either no pulmonary disability common in cases of farmer's lung. Asthma results or who are suffering from bronchitis, asthma or in tightness of the chest, wheezing, prolonged ex- other pulmonary disorders give precipitin reactions piration, and rhonchi quite distinct from the to extracts of mouldy hay in about 20% of cases. dyspnoea of farmer's lung which is out of all pro- These cases are the ones most likely to present portion to the auscultatory findings. There are no difficulty when one is deciding how much weight typical radiographic findings in asthma, and pul- can be placed on the serological results in deter- monary function studies show an airways obstruc- mining a diagnosis of farmer's lung; the final deci- tion, reversible with antispasmodics and not a sion must rest on the information that accrues from reduction in the diffusing capacity of the lungs the other aids in diagnosis. However, it must be unaffected by antispasmodics. Skin sensitivity tests remembered that sufferers from some other pul- using extracts of the responsible allergen show an monary disorders may also be suffering from super- immediate weal reaction in cases of asthma. The imposed farmer's lung. The presence of positive allergen may be contained in mouldy hay, and in precipitin reactions in a few farmers without obvious these instances a hypersensitivity to fungal extracts Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. 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20 J. Watkins-Pitchford may be found. No such immediate weal reaction of limited value since, disregarding the saprophytic occurs in cases of farmer's lung. Inhalation tests type of infection, normal people inhale and expec- using extracts of the relevant allergen give im- torate these widely dispersed spores without mediate reactions reversible by antispasmodics in suffering any disability. asthmatics whereas in similar tests on patients with Chronic Diffuse Interstitial Fibrosis of the farmer's lung a delayed reaction unaffected by anti- Lungs This comparatively rare disease of un- spasmodics occurs. known aetiology was first described by Hamman and Precipitin reactions in asthmatics are negative Rich (I944). The condition became known as the since the antibodies responsible for the immediate Hamman-Rich syndrome but the disease, as hypersensitivity reaction are non-precipitating. described by these authors, covered only a small Patients suffering from farmer's lung have circu- variant of the much wider condition now accepted lating precipitins and the test is therefore positive. as a single clinical entity. A compromise is fre- Pulmonary Aspergilosis The pathogenic quently used whereby the disease is known as member of the species is usually Aspergillus fumi- chronic diffuse interstitial fibrosis of the Hamman- gatus, although exceptionally other members may Rich type. Fibrosing alveolitis has recently been be responsible for the disease. The fungus pro- suggested. liferates on dead organic matter and it is not The outstanding clinical features are progressive infrequently a saprophytic invader complicating dyspnoea, unproductive cough, rales at the bases of existing pulmonary disease such as carcinoma, the lungs, clubbing of the fingers, and loss of weight. tuberculosis, lung abscess, unresolved pneumonia, The early radiographic changes are not unlike those and pneumoconiosis. The differential diagnosis in seen in farmer's lung with a fine mottling starting in these instances will be that of the underlying condi- the lower zones and spreading upwards as the tion. There is, however, an allergic variety of disease progresses. The mottling becomes coarser pulmonary aspergillosis in which inhalation of the and more confluent and may show cystic spaces fungal spores gives rise to episodes of asthma and usually noticeable first at the bases. fever accompanied by areas of pulmonary consolida- The pathology is essentially an oedematous copyright. tion and collapse, but the radiographic picture is thickening of the alveolar walls followed by an entirely different from that of farmer's lung. exudate in the alveolar spaces which appears to Sufferers may in fact be chronic asthmatics who, on retract and become organized with the oedematous exposure to the fungal spores, suffer episodic thickening as a fibrosis of the alveolar walls. aggravation of their asthma. The attacks usually A clear-cut case of this disease will not provide resolve within a few days but exceptionally they may the history of exposure to mouldy hay followed by go on for months. the episodes typical of farmer's lung. However, http://oem.bmj.com/ In these chronic cases an interstitial pulmonary difficulty may be encountered in differentiating fibrosis may result. The contains tenacious those cases of farmer's lung with an insidious onset. plugs incorporating filaments of the fungus and Pulmonary function tests will show a reduced eosinophil cells. There is also an eosinophilia in the distensibility of the lung with a reduction in the peripheral blood. Pulmonary function tests show diffusing capacity ofthe alveolar capillary membrane the airways obstruction observed in asthmatics and in both diseases. Serum precipitin reactions are of not a diminution of diffusing capacity except in great value, and a positive result provides presump- those rare cases where the disease has progressed to tive evidence that the interstitial fibrosis is in fact a on September 25, 2021 by guest. Protected interstitial fibrosis. Skin tests with appropriate late sequela of farmer's lung. If any doubt remains, extracts of A. fumigatus are positive giving an inhalation tests using extracts of mouldy hay should immediate weal reaction followed by a nodule, clinch the diagnosis. biopsy of which shows the cellular reaction to be Silo-filler's Disease This puzzling disease is eosinophilic. The trial inhalation of extracts of A. as yet uncommon in this country but it is worth fumigatus provokes immediate asthmatic reactions, bearing in mind since it is an acute respiratory reversible by antispasmodics. Sera from these disease of the agricultural community and is there- patients do not show precipitin reactions to the fore to be distinguished from farmer's lung. The appropriate antigens of farmer's lung. However, disease was described by Lowry and Schuman in sera from patients with farmer's lung may react with 1956 and is believed to be due to the inhalation of extracts of A. fumigatus but these reactions can be nitrogen dioxide given off during the early stages of distinguished from those due to the farmer's lung fermentation of silage. It is alleged that the use of antigen. artificial nitrogenous fertilizers and drought condi- The recovery of A. fumigatus from the sputum is tions at the time the silo is filled increase the danger. Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. Downloaded from

Farnwr's Lung 21 The typical history is one of being in a silo, or in hands, can distinguish the two conditions in a high the vicinity of one, from two hours to six days after percentage of cases. A typical farmer's lung re- it has been filled. Immediate cough, dyspnoea with action to test inhalation of extracts of mouldy hay a sensation of , and severe weakness are would be conclusive. noted, and these symptoms do not entirely clear up for the following two to three weeks. At the end of Other Pulmonary Diseases The fibrotic this period there is an acute illness accompanied by stage of farmer's lung may be confused with other fever, rapidly progressive dyspnoea, cyanosis, and pulmonary diseases giving rise to fibrosis. Further cough. Clinical findings consist of moist inspiratory conditions to be borne in mind are miliary tubercu- rales heard over both lungs. There is a marked losis, unresolved pneumonia, the collagen diseases, neutrophil leucocytosis, and the radiographic picture histoplasmosis, pneumoconiosis, and byssinosis. shows scattered, small, discrete opacities throughout The occupational pneumoconioses present as an both lung fields, very similar to those seen in miliary alternative diagnosis more frequently than might tuberculosis. The lungs in fatal cases contain very be expected since it is not uncommon for farming numerous uniformly distributed nodules of miliary and agricultural work to be a part-time or retired size which on histological examination are seen to be occupation in mining and industrial districts. bronchioles filled with a cellular fibrinous exudate with ingrowth of fibroblasts, from the bronchiole' Conclusions walls. The pathological picture is similar to that of the condition known as bronchiolitis fibrosa The disease of farmer's lung is probably as old as obliterans. the settled agrarian civilizations of temperate It is reasonable to suppose that, if this condition climates and has probably been responsible for is due to the inhalation of nitrogen dioxide, the serious ill-health through the ages. That it may be above description will vary according to the degree a serious disease is beyond question. Staines and ofexposure, and the inhalation of more concentrated Forman (I96I) recorded the length of illness in gas may well result in the more familiar picture of iii cases; in 44 of these there was more than three 'nitrous fume' poisoning. Delaney, Schmidt, and months' incapacity, and five patients were still in- copyright. Stroebel (I956) reported two patients with silo- capacitated after a year. The assessment of the final filler's disease, one ofwhom died in acute pulmonary disability after recovery from the illness showed that, oedema 36 hours after exposure to the fumes. out of I21 cases, 35 were judged to have a moderate or severe disability in following their regular Pulmonary Sarcoidosis The epithelioid-cell occupations and Io in doing other jobs. Only 5I pulmonary granuloma, characteristic of sarcoidosis, were judged to have been left with no disability at is found as a response to a variety of agents, and it all. If the 'speculative incidence' in the British Isles http://oem.bmj.com/ may well be that the disease is a non-specific host- of about i,ooo cases a year put forward by these tissue reaction rather than a single clinical entity. authors is correct, it seems that about 580 persons The list of agents capable of producing the sarcoid- a year are-left with some assessable disability and like tubercles is a long one, including acid-fast about 290 of these experience a moderate or severe bacilli, protozoa, fungi, beryllium, and zirconium. disability in following their regular occupations. Recently an acid-fast lipid material obtained from Such estimates of the total yearly incidence in the pine pollens has been shown to produce sarcoid-like British Isles cannot, of course, be used as an indica- lesions in experimental animals. tion of the number of successful claims that may be on September 25, 2021 by guest. Protected The essential pulmonary lesion of acute and sub- expected from the disease being prescribed under acute farmer's lung is indistinguishable patho- the Industrial Injuries Act. Broadly speaking, logically from that of sarcoidosis. The radiological persons eligible to claim industrial injuries benefit picture is also similar, but hilar node involvement is are confined to those who are employees, and the not found in farmer's lung. Both diseases may show evidence so far available suggests that a significant hyperglobulinaemia and reduced sensitivity to proportion of sufferers from farmer's lung are to be tuberculin. Pulmonary function tests may show a found among self-employed persons and their reduced distensibility and a diffusion defect in both families. conditions. The presence of evidence of sarcoidosis The disease normally presents a distinct clinical elsewhere in the body would of course exclude picture and, with the aid of the history and ancillary farmer's lung and the Kveim test may also be of investigations, it can be diagnosed in the majority of assistance. The diagnosis is likely to depend largely cases with reasonable certainty. Difficulty may be on the history and the results of the immuno- encountered in those patients who have a chronic electrophoretic precipitin test which, in experienced non-specific lung disease of some duration and on Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. Downloaded from

222. Watkins-Pitchford which some degree of pulmonary disability due to was further considered that a precise definition in farmer's lung becomes superimposed. However, terms of the effects of the disease might be advan- even in these patients it should be possible to recog- tageous, not only because ofthe number ofsynonyms nize the presence of serum precipitins against suit- by which farmer's lung is known but also because able extracts of mouldy hay, and the decision as to in this way the important distinction between how much of the disability should be attributed to farmer's lung and bronchitis may be kept in mind. farmer's lung will be assisted by further investigating The definition of the disease suggested in the Report the distensibility and diffusing capacity of the lungs. is therefore: 'pulmonary disease due to the inhalation of the dust APPENDIX of mouldy hay or of other mouldy vegetable produce and characterized by symptoms and signs attributable Prescription of Farmer's Lung under the to a reaction in the peripheral part of the broncho- National Insurance (Industrial Injuries) Act, pulmonary system and giving rise to a defect in gas 1946 exchange.' The Report, in considering the terms in which In June I963 the Minister of Pensions and the occupation cover should be drafted, pointed out National Insurance referred the following question that the majority of cases arise within the agricul- to the Industrial Injuries Advisory Council:- tural industry. However, evidence suggests that 'Whether, having regard to Section 55 (2) of the occasional cases may occur in other employments. National Insurance (Industrial Injuries) Act, 1946 the Some of these involve occupations ancillary to agri- respiratory complaint known as "farmer's lung", due to culture, such as threshing engineers and persons exposure to the dust of mouldy hay, mouldy straw or engaged in the transport of hay, but others do not; similarly contaminated agricultural produce, should be for example, if bagassosis is to be covered, persons prescribed under the Act and, if so, for what occupa- have tions.' manufacturing hardboard from bagasse would to be provided for. The Report considered that it The matter was referred by the Council to the would be possible to cover all such cases without copyright. Industrial Diseases Sub-Committee for detailed extending the field of cover too widely by the use of examination. In due course the Sub-Committee the following formula for the second column of the submitted a Report, which was adopted, to the Prescribed Diseases Schedule: Council and that Report was subsequently published by the Minister (Farmer's Lung, I964). 'Any occupation involving exposure to the dust of The Report in brief found that the farmer's lung mouldy hay or other mouldy vegetable produce.' syndrome appears to be caused by exposure to the This formula was, for technical reasons, subse- http://oem.bmj.com/ dust of mouldy vegetable matter; that a considerable quently amended by the Council. The final number of cases occur, almost exclusively within the occupational cover for the second column of the agricultural industry; that the condition often leads schedule reads: to prolonged incapacity and serious disability, so that a considerable sum in industrial injuries benefit 'Any occupation involving exposure to the dust of might be involved in an individual case, and that the mouldy hay or other mouldy vegetable produce by accident and pneumoconiosis provisions of the reason of employment (a) in agriculture, horticulture or in or handling in forestry; (b) loading, unloading, on September 25, 2021 by guest. Protected Scheme do not appear in practice to be adequate to storage such hay or other vegetable produce; or (c) in deal with the cases that occur. handling bagasse. Moreover, the judicious combination of the techniques available enabled the- disease to be The Report further recommended that, owing to diagnosed with reasonable certainty, and once diag- the complexities likely to arise over the diagnosis nosed it can be accepted as being due to the nature and assessment of the disease, the existing organiza- of the occupation. The relevant Section of the Act tion of the Pneumoconiosis Medical Panels should was therefore satisfied, and the Report recommends be used in settling these questions, though in other that farmer's lung should be prescribed. respects the disease should be treated as an ordinary The Report dealt at length with the definition of prescribed disease. farmer's lung for the purposes of prescription. It Finally the report drew attention to the need for considered that the disease, if prescribed, should providing some way to protect workers against this include pulmonary disability due to the inhalation serious disease. of the dust of other mouldy vegetable produce, the The recommendations of the Report were disease bagassosis being provided as an example. It accepted, and the disease was prescribed and added Br J Ind Med: first published as 10.1136/oem.23.1.16 on 1 January 1966. Downloaded from

Farmer's Lung 23 to the list of prescribed diseases by regulations Hunter, D., and Perry, K. M. A. (1946). Brit. J7. industr. (S.I., I965) which came into operation on June 2I, Med., 3, 64. Lowry, T., and Schuman, L. M. (I956). 7. Amer. med. Ass., I965. 162, I53. Murray, R., Dingwall-Fordyce, I., and Lane, R. E. (1957).

REFERENCES Brit. J. industr. Med., 14, 105. Pepys, J., Riddell, R. W., Citron, K. M., and Clayton, Y. M. Buechner, H. A. (I96I). Industr. Med. Surg., 30, 294. (I962). Thorax, 17, 366.

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