Abstract

The increasing awareness of problems with chemical pesticides used in greenhouses has led to a widespread use of biological control measures such as beneficial arthropods and microbiological pesticides. However, exposure to microbiological pesticides may confer a risk of immunoglobulin E-mediated sensitization.1 In a study by Baelum et al including 456 greenhouse workers, skin rash, nose and eye symptoms were seen in persons developing sensitization towards beneficial predatory mites during the 3-year study period and Groenewoud et al found a prevalence of 23% of sensitization to Amblyseius cucumeris in a cross-sectional study of 472 Dutch greenhouse workers.2 3 The predatory beneficial mites A cucumeris and Amblyseius californicus is known to cause sensitization and allergic symptoms from the skin, nose and eyes, but so far no case of occupational asthma caused by these predatory mites has been reported.

A 34-year-old male gardener, a non-smoker, was referred to our Department of Occupational and Environmental Health. The previous 10 years, he had been working in a tomato and green pepper nursery. During October to December each year, he was removing plants and cleaning up in all the greenhouses, including the sweet bell pepper greenhouses, and from January to September, he worked in the tomato nursery. A californicus was used as a biological control measure in the tomato nursery in 2003 and 2004 and A cucumeris in 2003 to 2007 in the neighboring sweet bell pepper greenhouses. During the past few years before referral, he had recurrent episodes of rash on the hands, wrists and face and symptoms of rhinitis and conjunctivitis with relief of symptoms on days off work. At the beginning of a new tomato season, he developed respiratory symptoms with wheezing and coughing. He was reported sick by his general practitioner and treated with antihistamines and a short-acting ß2-agonist, which relieved his symptoms completely. After his sick leave he returned to work but had to leave the tomato greenhouse after 1.5 h of work because of severe respiratory distress. He was seen by his general practitioner who found him severely asthmatic with a pronounced drop in lung function and with a flushing of the face and neck. The patient also complained of itchy and runny eyes. The patient was reported sick again and referred to our Department of Occupational and Environmental Medicine.

On admission he was free of symptoms and free of medication because his symptoms had resolved completely during his sick leave. At the allergy centre, the following tests were performed: (1) Skin prick test (birch, timothy, Artimisia, horse, dog, cat, Alternaria, Cladosporium, Dermatophagoides farinae, tomato plants (Sendrico and Aromata), latex and material from the tomato nursery (fresh tomato plants stem and leaf), withered tomato plant (plum tomato), red and green plum tomato and cocktail tomato); (2) histamine release test (HRT) for fresh tomato plant and flower, cultivation material, withered tomato plant, tomato stem and leaf, plum tomato, cocktail tomato and dust from tomato nursery. (3) immune-specific immunoglobulin E (birch, timothy, Artemisia, Alternaria, Cladosporium, Dermatophagoides pteronyssinus and D farinae, tomato, Aspergillus niger and Cephalosporium acremonium); (4) patch test (European Standard Series, tomato, tomato leaf and stem, tomatoleoresin, latex and vinyl gloves). All tests were negative. A slight positive skin prick test reaction to D pteronyssinus was seen, but this reaction was not reproducible when the test was repeated.

A challenge test was then performed where the patient was handling plant material from the tomato nursery in a plastic bowl. After 5 min of handling the plant material, the patient developed respiratory symptoms with a drop in forced expiratory volume in 1 s (FEV1) equivalent to 72% of the expected (FEV1=2.95). To test for sensitization to predatory beneficial mites, allergen preparation was made by extraction of the following species: Tetranychus urticae, Hypoaspis miles, A cucumeris and A californicus (for details on allergen preparation, see Baelum et al3). HRT (RefLab, Copenhagen, Denmark) revealed clear positive reaction (class V and VI) to A cucumeris and A californicus, respectively, and no reaction to T urticae or H miles. Skin prick testing revealed a positive reaction to A cucumeris but not to A californicus, T urticae or H miles. A nasal challenge with a mix of A cucumeris, A californicus, T urticae and H miles was performed resulting in a forceful clinical reaction including nasal blockage and respiratory distress. Lung auscultation revealed prolonged expiration, and lung function test showed a marked drop in FEV1 from 4.2 to 3.6 litres. The patient was treated with terbutaline inhaler, which restored lung function and resolved symptoms completely. HRT was repeated again with a marked positive reaction to A cucumeris and A californicus class V and VI respectively.

Conclusion and policy implications
This is the first report documenting occupational asthma caused by A cucumeris and A californicus and emphasizes the need for regulation, guidelines and preventive measures when handling these mites and mite-treated plants. Further studies are needed to evaluate antigen exposure and identification of workers at risk.

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