The effects of occupational exposure to organic dusts on respiratory health have been investigated, but the mechanisms through which these respiratory effects are caused are not yet well understood.
Many of the micro-organisms found in dust generated during composting are known respiratory sensitisers. Fungi such as Aspergillus spp., Penicillium spp., Cladosporium spp., Rhizopus spp. and Alternaria spp. are well known allergens28'51-53 while Gram-negative bacteria may also be a source of endotoxin.54 Inhalation of organic dust can cause a range of immunological respiratory symptoms which can be divided into four types of respiratory reaction as well as, very infrequently, infection.29'55-57
When a patient is sensitised to airborne allergens, exposure to those allergens can trigger the immunoglobulin E (IgE) pathway of the immune system causing allergic rhinitis (inflammation of the nasal passageways) or allergic asthma (upper respiratory tract broncho-constriction). Rhinitis and asthma frequently coexist in the same patient and both diseases are increasing in prevalence in the general population. Organic dust rhinitis and asthma are not caused by a single allergen present in the dust; different allergens may be responsible in different patients.29'58-60 Workers handling compost are often exposed to higher levels of allergens than the general population and the species to which they are exposed may differ.
51 J. Dutkiewicz, L. Kus, E. Dutkiewicz and C.P.W. Warren, Ann. Allergy, 1985, 54, 65-68.
52 J. Dutkiewicz, S. A. Olenchock, W. G. Sorenson, V. F. Gerencser, J. J. May, D. S. Pratt and V. A. Robinson, Appl. Environ. Microbiol., 1989, 55, 1093-1099.
53 J. Lacey, Ann. Agric. Environ. Med., 1995, 2, 31-35.
54 J. Dutkiewicz, Zbl. Bäk. I. Abt. Orig., 1976, 236, 487-508.
55 M. Chan-Yeung, D.A. Enarson and S.M. Kennedy, Am. Rev. Respir. Dis., 1992, 145, 476-487.
56 J. Lacey, Postharvest News Info., 1990, 1, 113-117.
57 R. Rylander, Ann. Agric. Environ. Med., 1994, 1, 7-10.
59 A. D. Blainey, M. D. Topping, S. Oilier and R. J. Da vies, J. Allergy Clin. Immunol, 1989,84,296-303.
60 E. Zuskin, E.N. Schachter, B. Kanceljak, J. Mustajbegovic and T. Wiltek, Int. Arch. Occup. Environ. Health, 1994, 66, 317-324.
Chronic Bronchitis and Chronic Obstructive Pulmonary Disease
Chronic bronchitis is an inflammation of the mucous membrane of the bronchial tubes characterised by chronic cough, hypersecretion of phlegm and/or sputum and dyspnea and/or airways obstruction. The role of airborne fungal spores is uncertain, but airborne bacterial endotoxins may be involved in these diseases.29'61 '62 Clapp et al.61 found evidence of additional endotoxin independent mechanisms of lung inflammation.
Extrinsic Allergic Alveolitis or Granulomatous Pneumonitis
Extrinsic allergic alveolitis or granulomatous pneumonitis is generally an occupationally-related disease. Extrinsic allergic alveolitis is a T lymphocyte CD8 predominantly, granulomatous, inflammatory reaction of the peripheral gas exchange tissue. Onset can be acute or insidious.63 Repeated exposure to large concentrations of spores, in excess of 106 spores m "3 of air (and mostly 1-5 /im in diameter) has been suggested as the cause of acute symptoms.55 However prolonged exposure to lower concentrations of spores may also cause chronic symptoms.64 Acute symptoms occur 4-6 hours after exposure to the dust. These are chills, fever, dry cough, malaise and increasing breathlessness and, eventually, permanent lung damage may occur.28'29'65 The characteristic immunological feature is the occurrence of predominantly IgG antibodies against specific antigens in the organic dust. Mushroom workers' lung has been linked to the inhalation of actinomycete spores associated with the mushroom compost.66'67 Farmers' lung disease and is caused by inhalation of the fungal and actinomycete spores present in large numbers in contaminated organic dusts; the actinomycetes Saccharopolyspora (Faenia) rectivirgula and Thermoactinomycetes spp. have been implicated.56
Toxic pneumonitis or organic dust toxic syndrome (ODTS) is an acute illness occurring during, or shortly after, high exposure to airborne dust. Influenza-type symptoms develop, with leucocytosis and fever. No prior sensitisation is needed, antibodies do not develop and respiratory symptoms may or may not occur. The aetiology is unknown, but this also may be caused by inhalation of mycotoxins or endotoxins present in organic dust.29'55 Further evidence for the role of endotoxins in ODTS has been provided by human challenge studies. Challenge
61 W. D. Clapp, S. Becker, J. Quay, J. L. Watt, P. S. Thorne, K. L. Frees, X. Zhang, H. S. Koren, C. R. Lux and D. A. Schwartz, Am. J. Resp. Crit. Care Med., 1994, 150, 611-617.
62 S. A. Olenchock, D. C. Christiani, J. C. Mull, T. T. Ye and P. L. Lu, Biomed. Environ. Sci., 1990, 3, 443-451.
63 J.N Fink, J. Allergy Clin. Immunol., 1973, 52, 309-317.
64 J. Lacey and J. Dutkiewicz, J. Aerosol. Sci., 1994, 25, 1371-1404.
65 S. Webber, G. Kullman, E. Petsonk, W.G. Jones, S. Olenchock, W. Sorenson, J. Parker, R. Marcelo-Baciu, D. Frazer and V. Castranova, Am. J. Ind. Med., 1993, 24, 365-374.
66 J.G. Kleyn, W.M. Johnson and T.F. Wetzler, Appl. Environ. Microbiol., 1981, 41, 1454-1460.
67 J. Lacey, P. A. M. Williamson and B. Crook, in Aetiology, ed. M. Muilenberg and H. Burge, CRC/Lewis Publishers, New York, 1996.
studies with pure endotoxin have shown that in normal healthy subjects an inhalation of over 30-300/xg endotoxin can cause a clinical response.68"70 Inhalation of endotoxin can also result in decreases in lung function and inflammatory responses. A decrease in lung function is caused by inhalation of over 80 fig of endotoxin in healthy subjects and over 20 fig endotoxin in asthmatics;70"72 this response is significant 30 minutes after endotoxin inhalation and lasts five hours or more. Inflammatory responses to an acute inhalation of LPS in healthy subjects have been reported to occur after inhalation of less than 0.5 fig. Endotoxins have strong adjuvant effects on the reactions to antigens and increase the production of antibodies, they can have a synergistic effect on the skin prick test response and may facilitate the development and persistence of hypersensitivity pneumonitis and allergic asthma via their inflammatogenic and adjuvant properties.49'69'73 The adjuvant effect could be very important in the context of occupational exposure to the mixed allergens and toxins in compost dust.
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