House-dust mite species in Bloemfontein, South Africa

House-dust mites (HDMs) are an important source of allergens that are reputed to act as a trigger for atopic disease. Climatic conditions in parts of South Africa are not suitable for their proliferation, and there is doubt whether they occur on the Highveld. We studied whether HDMs occur in homes in Bloemfontein, Free State. Methods. Ten houses were sampled over a 1-year period. Dust was collected monthly or quarterly from a mattress, a bedroom floor and the living room floor of each house and examined for the presence of HDMs. Climate data were collected during the same period and a questionnaire was completed by home-owners to gather data on indoor factors that could influence mite proliferation. Results. HDMs were regularly found in 3 houses (30%). Dermatophagoides farinae was the dominant species (97.5%). The highest numbers were found in winter, when climatic conditions were the least favourable. Climatic conditions never met the requirements for active proliferation of the mites. Indoor factors that may have promoted mite proliferation in some houses were artificial heating (especially under-floor heating), en-suite bathrooms and lack of adequate ventilation during the winter months. Conclusion. HDMs do occur in central South Africa, owing to a microclimate created indoors. Adequate ventilation, to reduce indoor humidity, should suffice to reduce mite numbers and prevent atopic symptoms induced by them.