Equine intradermal test threshold concentrations for house dust mite and storage mite allergens and identification of stable acari fauna.

The presence of house dust mites (HDMs) and storage mites (SMs) in the human environment has been established worldwide and both contribute to atopic disease consisting of atopic dermatitis, asthma and allergic rhinitis in some individuals. The Dermatophagoides, Acarus, Tyrophagus and Lepidoglyphus mite genera contribute to the pathogenesis of atopic disease. HDMs and SMs have also been implicated in atopic dermatitis in veterinary medicine. Extensive work has been done for canine mite induced allergic patients, but relatively little information is available for equine allergic patients. Intradermal testing is performed in veterinary patients to identify environmental antigens that cause disease with the intent of formulating allergen-specific immunotherapy. Equine HDM and SM intradermal test (IDT) threshold concentrations (TCs) for the Midwestern United States are unknown. The mite stable fauna for the Midwestern region of the United States has not been determined. The objectives of this study were to determine IDT TCs for HDM and SM species, to quantify mite-specific IgE concentrations in thirty-eight clinically normal horses over two seasons and to characterize the mite fauna of a stable in this region across three seasons. Subjective measurements of IDT reactions were used to determine the TCs for Dermatophagoides farinae, Dermatophagoides pteronyssinus, Acarus siro, Tyrophagus putrescentiae and Lepidoglyphus destructor. The reactions were scored using a scale of 0 to 4+. Allergen testing concentrations ranged from 1:320,000-1:20,000 w/v for HDMs and 1:160,000-1:5,000 w/v for SMs. Threshold concentrations were defined as the highest concentration of a mite allergen where =10% of horses had a positive subjective reaction (=2+) at 15 min. Analysis of equine serum-specific IgE was performed using a commercially available allergen-specific IgE ELISA test. Specialized mite traps and modified flotation methods were used to collect mites in spring, late summer and winter from nine locations on one farm. Selected locations for mite collection represented the three different stabling environments used, bedding types, feed materials or combinations thereof. A single-baited mite trap was placed at each of the locations for a four-day period (96 h), while 200 g of material was gathered from each site on the fourth day for flotation. An acarologist morphologically identified and quantified the species of HDMs and SMs collected. Subjectively determined TCs were: 1:80,000 w/v for Dermatophagoides farinae in both seasons, 1:80,000 w/v in spring and 1:160,000 w/v in late summer for Dermatophagoides pteronyssinus, 1:40,000 w/v in spring and 1:20,000 w/v in late summer for Acarus siro, 1:20,000 w/v for Lepidoglyphus destructor in both seasons, and 1:20,000 w/v in spring and 1:10,000 w/v in late summer for Tyrophagus putrescentiae. In both seasons, at least one horse had a positive serum IgE result for each HDM or SM evaluated. Negative serum IgE concentrations for all mite species were present in 55% of horses in spring and 66% in…