Atopic dermatitis is one of the most common causes of pruritus in dogs. Allergies to the house dust mite (Dermatophagoides) are common. In addition, storage mite (Tyrophagus, Acarus, Lepidoglyphus) sensitivity is common, but the relevance to canine atopic dermatitis is still unclear. Dry dog food is a documented source of exposure to these mites. In the present study, house dust and storage mite contamination of dog food was evaluated in 10 homes in the UK between April and August 2009. Ten identical bags of dog food from the same batch were divided equally among the original bag (sealable closure), a paper bag, and a plastic box with a locking lid. The samples were all stored in the same location, and temperature and humidity were recorded. The food bags and container were opened once daily to mimic normal feeding. Samples of dog food were collected on days 0, 30, 60, and 90. House dust samples were collected on day 90. All samples were tested for mites using Acarex tests for guanine, Der p 1 ELISA, and mite flotation. The Acarex test was negative in all food samples but positive in all house dust mite samples. Mites were found by flotation in 6 of 10 paper bags, 3 of 10 plastic bags, 1 of 10 plastic boxes, and 9 of 10 house dust samples. House dust mite numbers and ELISA test results were 10 to 1000 times higher in house dust than in food samples; bedding and carpeting were significantly associated with increased levels of house dust mites. The storage of food in plastic boxes prevented mite contamination for the duration of the study. The authors conclude that while house dust and storage mites can contaminate dry foods, food presents minimal risk compared with bedding, carpets, and rugs and that mite exposure can be minimized by storing food in plastic boxes for no more than 3 months.

Commentary:
The importance of house dust mite allergy is well-established in veterinary dermatology. Currently, the importance of storage mites is unclear. The focus on dog food and mites is relatively new and stems from research showing that house dust mites can survive and reproduce on dog food especially if mold and moisture are present. The results of numerous studies vary with temperature and geography; mites thrive in warm moist climates. This study quite simply shows that dog food should be stored in sealed plastic containers and implies that owners should purchase amounts that are consumed in a reasonable time. Although storage mites were found in the food, their numbers were small compared with the number of house dust mites found in the homes, especially on carpets and rugs. The Acarex test is a dipsticktype test that detects house dust mite feces. Several years ago I used this test to look for house dust mites in my own home and the most heavily contaminated site was the dog bed.—Karen Moriello, DVM, Diplomate ACVD

House dust and storage mite contamination of dry dog food stored in open bags and sealed boxes in 10 domestic households. Gill C, McEwan N, McGarry J, Nuttall T. VET DERMATOL 22:162-172, 2011.