Storage mite contamination of commercial dry dog food in south-eastern Australia

Objective To evaluate contamination of unopened and opened stored sources of commercial dry dog food by viable storage mites. Design Prospective laboratory and field study. Material and methods Samples were collected from nine brands of previously unopened bags (new bags) of dry food and 20 field sources of stored dry food in homes in Sydney and Canberra, Australia. All samples were initially examined for the presence of mites using a stereo-binocular microscope and then placed in separate filter-paper-sealed containers. Field samples were incubated at an average temperature of 29 degrees C and 78% relative humidity (RH) for 5 weeks and then at average 26 degrees C/83% RH for 8 weeks. Paired new-bag samples were stored under room conditions (average 23 degrees C/47% RH) and controlled incubator conditions (average 26 degrees C/80% RH) for 6 weeks. All samples were thoroughly examined for mites, mite eggs and visible mould once weekly using a stereo-binocular microscope. Results Storage mites were not visualised in any of the field samples or in new-bag samples stored at room temperature. Storage mites, identified as Tyrophagus putrescentiae, were visualised in increasing numbers in seven of nine new-bag samples after incubation, with first mites and then eggs evident after 3 weeks of incubation. Conclusions We confirmed the presence of viable storage mites in a range of previously unopened commercial dry dog foods in Australia and confirmed the possibility of heavy storage mite contamination for dry food stored under conditions of moderate temperature and high humidity. These findings have relevance to storage mite and/or dust mite sensitivity in canine atopic dermatitis.