Quick Dips

Mighty Problems with Mites

Houses in Wellington and Christchurch are coming under close scrutiny to see what dangers are lurking in their carpets and rugs. Of particular interest are the quantities and varieties of tiny house dust mites to be found; the mites have been implicated in New Zealand's high incidence of asthma.

No comprehensive studies of the levels of house dust mites in New Zealand have been undertaken, but now the Wellington Asthma Research Group is working on quantifying the levels of house dust mites in Wellington, and the Canterbury Respiratory Research Group is sampling houses in Christchurch to provide information on the numbers and species of house dust mite there.

One of the hot issues in environmental asthma at the moment is the role that house dust mite allergen plays in the sensitisation of the airways. Studies overseas have shown that up to 80% of asthmatics can be sensitive to this allergen. Levels can vary markedly between different geographical regions ranging from none in very dry environments to much higher levels in humid environments.

There are many species of house dust mite but the most prevalent one appears to be Dermatophagoides pteronyssinus. These are tiny creatures barely visible to the naked eye. They like to live in damp, humid environments and have a tendency to accumulate in soft furnishings, carpets and beds. Their main diet is shed human skin scales and they have been described as a walking stomach and reproductive system. The allergen which makes people sensitive to house dust mite is contained in the faecal coating which is produced by these creatures.

House dust mite allergen levels are known to be lower in public buildings than in domestic dwellings. The Wellington and Christchurch asthma research groups will also be looking at the differences in building construction, heating, ventilation and occupancy between public and private dwellings in an effort to understand the building codes required to effect significant reduction of indoor allergen.

The Canterbury team, working under the direction of Dr Ian Town, from the Christchurch School of Medicine, are involved in a variety of studies looking at the causes, treatment and management of asthma, pneumonia and chronic obstructive airways disease. The research group works in close collaboration with Canterbury Respiratory Services at Christchurch Hospital.

Further studies are being planned to explore the relationships between house dust mite allergen levels, atopy and asthma prevalence and severity. The research programme will also include studies addressing the role of house dust mite reduction measures as a strategy to control asthma.