Seasonal asthma and the house-dust mite in tropical Africa.

The relationship between seasonal asthma and sensitivity to the house-dust mite has been investigated in a country with large seasonal variations in relative humidity. Of seventy-eight African asthmatics, 64.1% gave a history probably suggestive of sensitivity to house-dust, and 55.1% a history strongly suggestive of such sensitivity. On skin testing, 35.9% had strong reactions to the house-dust mite Dermatophagoides pteronyssinus, compared with 1.9% of fifty-one matched controls without symptoms of chest disease. Few had either a history or skin tests suggestive of pollen or mould sensitivity. Most of the asthmatics were worse during the hot, wet season when the humidity is highest. This is also the time when in-patient asthmatics are most numerous. D. pteronyssinus grows well in warm, damp conditions and it is suggested that sensitivity to this mite may play a significant role in the marked seasonal changes seen in our asthmatic patients.