Reactivity to intradermal injections of extracts of house dust and housedust mite in healthy dogs and dogs suspected of being atopic

Abstract

Summary Fifty dogs underwent intradermal allergy testing with housedust mite and house dust extracts, using concentrations recommended by the manufacturer. Twelve dogs (group I) were healthy dogs obtained from a pound; 12 dogs (group II) were healthy, privately owned dogs; 15 dogs (group III) were suspected of being atopic and had had multiple positive reactions to intradermal injections of allergens of specific trees, weeds, grasses, or molds; and 11 dogs (group IV) were suspected of being atopic, but only had had positive reactions to intradermal injections of housedust mite, house dust, and flea antigen extracts. Use of the concentrations of housedust mite and house dust extracts currently recommended for intradermal allergy testing resulted in false-positive reactions in 14 of 24 (58%) and 12 of 24 (50%) healthy dogs tested, respectively. Differences in number of dogs with positive reactions or grade of reaction to housedust mite or house dust allergens were not detected between groups of healthy dogs (groups I vs II), between groups of suspected atopic dogs (groups III vs IV), or between healthy dogs and dogs suspected of being atopic (groups I and II vs III and IV). Therefore, clinical importance of positive results of intradermal allergy testing of house dust or housedust mite allergens was equivocal for dogs suspected of being atopic. Threshold concentrations for intradermal allergy testing were determined in 24 healthy dogs (group I and II) by intradermal administration of 5 dilutions each of housedust mite extract and house dust extract. Positive test results to various concentrations of housedust mite extract were observed in 22 dogs at 1:1,000 wiv, 14 dogs at 1:5,000 wiv, 5 dogs at 1:10,000 ww, 4 dogs at 1:25,000 wv, and 1 dog at 1:50,000 ww. Positive test results to various concentrations of house dust extract were observed in 21 dogs at 500 protein nitrogen units (pnu)/ml, 12 dogs at 100 pnu/ml, and 3 dogs at 50 pnu/ml, but none of the dogs had positive results at 20 and 10 pnu/ml, respectively. Threshold concentrations for housedust mite (1:50,000 w/v) and house dust (20 pnu/ml) extracts were subsequently used for intradermal allergy testing of 9 dogs (group V) that were considered to be atopic and that had had multiple positive test results after intradermal injection of specific allergens. Positive reactions to intradermal injections of threshold concentrations of housedust mite and house dust extracts were observed in 6 of 9 and 7 of 9 atopic dogs, respectively. Analysis of the results was suggestive that house dust and housedust mite extracts can be properly diluted to threshold concentrations for intradermal allergy testing without adversely affecting their diagnostic value. Lower concentrations of housedust mite and house dust extracts than are currently recommended should be used for intradermal allergy testing to avoid false-positive results.