Immediate intradermal flea‐antigen reactivity in dogs in a flea‐scarce environment

Abstract

The aim of this study was to determine the prevalence of intradermal test (IDT) reactions to flea antigen in dogs in a flea‐scarce environment. Seventy‐three client‐owned dogs without present or prior exposure to fleas were used. Forty dogs had a history of, and clinical signs compatible with, atopic dermatitis (AD), after exclusion of other causes of pruritus, and 33 dogs were healthy or had some disease other than AD. A questionnaire was used to collect information about previous ectoparasitic infestations. An aqueous extract of whole bodies of Ctenocephalides spp. (Nelco Laboratories Inc., NY, USA) was used for IDT at a concentration of 1:1000 w/v. None of the dogs had been treated with corticosteroids or antihistamines within the previous 3 months. A positive reaction was defined as a wheal that was equal to or larger in diameter than the average of the saline and histamine controls. Two of the dogs with clinically diagnosed AD and none of the nonatopic dogs had immediate skin‐test reactions to flea antigen. The prevalence (2.7%) for positive IDT against flea extract found in this study is low compared with studies performed in a flea‐rich environment. Immediate skin‐test reactivity against flea antigen in clinically normal dogs in flea‐endemic areas could represent subclinical hypersensitivity or true false‐positive reactions (due to skin irritation). Thus, these findings indicate that false‐positive reactions against whole‐body flea antigen from Nelco in dogs not exposed to fleas are rare.