House dust mite allergen accumulation on sheepskins

Sheepskins, which are often used as infant bedding in New Zealand, are known to harbour large quantities of house dust mites and their allergens. In this study we determined the rate of accumulation of the house dust mite allergen, Der p 1 on new sheepskins, and the effects of washing and dry cleaning on its removal.

New sheepskins were placed on living-room floors (n = 6) and mattresses (n = 6) in six domestic dwellings in Wellington. Sheepskin dust samples were collected by vacuuming before placement, and at two, four and six weeks, after which they were warm-washed. They were replaced for a further six weeks, then dry-cleaned. Dust samples were collected before and after washing and dry-cleaning, and from mattresses and living-room floors. Dust samples were analysed for Der p 1 by double monoclonal antibody ELISA.

Der p 1 levels rapidly increased in sheepskins placed on living-room floors and mattresses to a geometric mean level (range) of 9.0 micrograms/g (1.1-102.2) and 29.4 micrograms/g (5.3-131.1) at six weeks, respectively. After warm-water washing and replacement for a further six weeks, these levels were higher at 75.5 micrograms/g (50.1-260.4) and 31.9 micrograms/g (11.1-75.2), respectively. Sheepskin Der p 1 accumulation correlated with mattress (r = 0.78), and living-room floor Der p 1 levels (r = 0.94). Warm water washing and dry-cleaning reduced sheepskins Der p 1 levels by a mean of 79.2% and 95.3%, respectively.

Sheepskins rapidly accumulate house dust mite allergens from the domestic environment. Due to very high levels and rapid accumulation of Der p 1, sheepskins as infant bedding should be discouraged for infants at risk of sensitisation to house dust mites. If they are to be used then it is important that they are washed or dry-cleaned regularly.