Flea Antigen Research Articles

A small-scale open-label study of the treatment of canine flea allergy dermatitis with fluralaner.

Fluralaner is an isoxazoline systemic insecticide and acaricide that provides persistent flea-killing activity on dogs for 12 weeks. European and US field studies have shown that fluralaner treatment alleviates the signs of flea allergy dermatitis (FAD) in client-owned dogs. To assess the clinical response in FAD affected dogs over the 12-week period following a single oral fluralaner treatment. Twenty client-owned dogs were diagnosed with FAD on the basis of compatible clinical signs and a positive response in flea antigen tests, using intradermal and or serological methods. An open-label small-scale study with all dogs receiving a single oral fluralaner treatment. All enrolled dogs were diagnosed with FAD and then clinically monitored at 4-week intervals for 12 weeks. Twenty dogs completed the study. All dogs were flea-free at all post-treatment assessments except for one dog that had a single flea at the first post-enrollment assessment at 4 weeks. At the 4-week post-treatment assessment active FAD signs had resolved in all dogs; at 8 weeks post-treatment, two dogs showed mild signs. All clinical signs of FAD had resolved at the final assessment of 12 weeks after treatment. A single administration of fluralaner alleviated or resolved signs associated with FAD in all treated dogs over the recommended 12-week treatment period.

Differences in Systemic and Skin Migrating-Specific CD4+ T Cells in Papular Urticaria by Flea Bite

Background: Papular urticaria by flea bite is a chronic allergic condition in which clinical improvement may occur at the age of 7 years, thus representing a natural model of acquired immunologic tolerance in humans. The aim of this study was to characterize regulatory cells and specific responses to flea antigens of CD4⁺ T lymphocytes expressing cutaneous migration markers in patients with papular urticaria caused by flea bite and with different disease evolution times. Methods: Cell populations were characterized by flow cytometry in samples from patients and healthy controls. Specific cell stimulation was performed with a complete flea body extract. The Mann-Whitney U test was used for comparisons. Results: Total dendritic cells were lower in patients than in healthy controls. No quantitative differences were found in CD4 regulatory T cells. CD4⁺ T cells from patients produced more IL-4, lL-10, IL-17, and IFN-γ. Patients who experienced the onset of symptoms within the first 5 years of age showed a greater percentage of local (cutaneous lymphocyte antigen +) IL-4- and IL-17-producing cells, while patients who experienced the onset of symptoms after the age of 5 years had a higher percentage of systemic (cutaneous lymphocyte antigen –) IL-10-producing cells. Conclusion: Analysis of the cellular immune response against whole flea antigen in patients with papular urticaria by flea bites suggests a possible participation of inflammatory cytokines in the skin reaction (Th17) and a systemic control mechanism (IL-10). This pattern of cytokine production in patients could be a consequence of an impaired dendritic cell population.

Specific pattern of flea antigen recognition by IgG subclass and IgE during the progression of papular urticaria caused by flea bite

Background Papular urticaria caused by flea bite presents clinical symptoms of a hypersensitivity reaction accompanied by skin lesions. However, the pattern of recognition by different antibody isotypes during the progression of the disease is unknown. This study evaluated variations in immunoglobulin E and immunoglobulin G subclass antibody responses to flea antigens during the progression of papular urticaria caused by flea bite Methods Twenty-five patients clinically diagnosed with papular urticaria due to flea bite were included. Ten healthy children were included as controls. Recognition of antigens from complete flea body extract by patients and healthy controls was determined using immunoblot assays. Results The results revealed that patients with 2–5 years of papular urticaria evidenced more IgE bands than those with shorter or longer durations of symptoms. In contrast, healthy children showed a predominance of immunoglobulin G1 and immunoglobulin G3. The majority of the recognised antigens were low molecular weight proteins (<90 kDa). Proteins with molecular weights between 16–20, 21–25, and 31–35 kDa showed different patterns of recognition between patients and healthy children. Conclusion The predominant specific antibody isotypes vary according to the time elapsed since the onset of symptoms in papular urticaria caused by flea bite.

Monitoring of basophil sensitization to antigens of the cat flea (Ctenocephalides felis felis): a new tool for the diagnosis of feline flea bite hypersensitivity?

Suitability of blood basophils for in vitro diagnosis of flea allergy dermatitis (FAD) or flea bite hypersensitivity was studied in cats. A functional in vitro test (FIT) for sensitized type I allergic effector cells was used to evaluate the degree and kinetics of in vivo basophil sensitization against flea antigens in cats under long-term flea exposure. FIT results were compared with intradermal (IDT) and serological testing. Before, during, and after weekly repeated exposure to Ctenocephalides felis; 14 cats were repetitively FIT-assessed for general and flea-specific sensitization. In three cats, flea-specific sensitization was seen before and throughout flea exposure. Five cats, although generally sensitized, never developed a flea-specific sensitization. Six cats initially FIT-negative became sensitized for flea antigen during flea infestation. Induction, upregulation, and binding of C. felis-specific sensitizing antibodies to basophils during flea challenge may explain the developing sensitization in these cats. Strong discrepancies between the levels of flea-specific circulating IgE and basophil sensitization contrasted comparable results for basophil and mast cell sensitization using FIT and IDT, respectively. Hence, the FIT might provide an immunological supplement to the clinical diagnosis of FAD in cats by elucidating the state of basophil-sensitization to flea antigens. And it may be a comfortable alternative to IDT.

A rodent model for allergic dermatitis induced by flea antigens

There have been very few reports of experimentally induced animal models of allergic dermatitis, an immunologic disorder. This report describes the induction of histopathology confirmed allergic dermatitis in C57BL/6 mice along with the consistent clinical sign of alopecia following the administration of flea antigens emulsified in complete Freund's adjuvant (CFA). By comparing different strains of mice, routes of injection, types of adjuvants and different dosages of flea antigens, C57BL/6 mice were found to be most susceptible to flea antigens administered intramuscularly (i.m.) and subsequently developed dermatologic excoriations and local alopecia. The level of specific IgE reactive to flea antigens in C57BL/6 mice after the onset of clinical signs was significantly higher than such levels in mice without clinical signs, suggesting that flea antigen-specific IgE level can be correlated to the severity of allergic hyper-reaction. CD4 + T lymphocytes and IL-4 rather than IL-10, or IFN-γ were found to be the predominant cytokines associated with the clinical onset of allergic symptoms in C57BL/6 mice. Further, histopathologic analysis indicated that not only mast cells had infiltrated into the area of the skin lesion, but the damage was found to be at a stage where mast cells were degranulating causing considerable exacerbation of the local injury. In conclusion, this murine allergic dermatitis model induced by flea antigens may provide a useful means to evaluate vaccines or immunodulatory drugs; thus providing researchers with a tool to study allergy-related disorders and other parameters needed in the area of allergic investigations.

Evaluation of three different histamine concentrations in intradermal testing of normal cats and attempted determination of ‘irritant’ threshold concentrations for 48 allergens

The purpose of this study was to determine the optimal histamine concentration and 'irritant' allergen threshold concentrations in intradermal testing (IDT) in normal cats. Thirty healthy cats were tested with three different histamine concentrations and four different concentrations of each allergen. The optimal histamine concentration was determined to be 1: 50,000 w/v (0.05 mg mL(-1)). Using this histamine concentration, the 'irritant' threshold concentration for most allergens was above the highest concentrations tested (4,000 PNU mL(-1) for 41 allergens and 700 PNU mL(-1) for human dander). The 'irritant' threshold concentration for flea antigen was determined to be 1:750 w/v. More than 10% of the tested cats showed positive reactions to Dermatophagoides farinae, Dermatophagoides pteronyssinus, housefly, mosquito and moth at every allergen concentration, which suggests that the 'irritant' threshold concentration for these allergens is below 1,000 PNU mL(-1), the lowest allergen concentration tested. Our results confirm previous studies in indicating that allergen and histamine concentrations used in feline IDT may need to be revised.

Serological, intradermal and live flea challenge tests in the assessment of hypersensitivity to flea antigens in cats (Felis domesticus)

The results of intradermal testing with three commercial flea antigens and a serological test for IgE antibodies to flea antigens were compared with live flea challenge in cats. Eight control cats with no prior flea exposure had negative serological test and flea challenge results. By contrast, 17 out of 27 cats with previous flea exposure showed immediate reactivity to flea challenge; reactivity at 6, 24 and 48 h after flea exposure was noted in 12, 16 and 21 cats, respectively. Seventeen of these cats had positive serological test results. Seven cats showed immediate intradermal test reactions to the ARTU allergen, six reacted to the Biophady allergen, and six reacted to the Greer allergen. Intradermal test reactivity was less frequent at the other time points. Using the results of the flea challenge as the 'gold standard' for the presence or absence of sensitisation to fleas, the sensitivity and specificity of the serological test was 0.88 and 0.77, respectively. Sensitivities of the intradermal tests at the four time points ranged from 0 to 0.33, whereas the specificities ranged from 0.78 to 1.0. Live flea challenge is better able to detect cats with hypersensitivity to fleas than either intradermal or serological testing.

Patients with papular urticaria have IgG antibodies to bedbug (Cimex lectularius) antigens

IgG and IgE against salivary gland proteins of bedbug (Cimex lectularius) were assessed in comparison with mosquito (Culex pipiens) and flea (Pulex irritans) antigens in the sera of papular urticaria patients (group I), siblings without papular urticaria (group IIa), patients' parents (group IIb), and healthy controls (group III) (Immunoblotting). Anti-C. lectularius IgG was significantly recognized at 66 and 10 kDa in 40% of group I, besides others ranging from 45 to 107 kDa. Group IIa significantly reacted with 70 kDa (57.1%). Group IIb reacted with 21 and 8.5 kDa (26.7%). Sixty percent of group IIb and 100% of group III significantly identified a band of 12.5 kDa. IgG against C. pipiens was significantly recognized at a range of 18-105 kDa in group I, IIb (115, 7 kDa), and III (58, 50 kDa). Anti-P. irritans IgG was significantly recognized by group I (100, 70 kDa) and group IIa (60, 35 kDa). IgE response was confined to C. pipiens at 115 and 54 kDa in groups I and III, respectively, besides 68 and 58 kDa in group IIa. It is concluded that IgG is present against C. lectularius, C. pipiens, and P. irritans in papular urticaria and may contribute to its pathogenesis.

Immune dysregulation in flea allergy dermatitis—A model for the immunopathogenesis of allergic dermatitis

Background Flea allergy dermatitis (FAD) is a common skin disease in dogs and can be induced experimentally. It often coexists with other allergic conditions. So far no studies have investigated the quantitative production of cytokine mRNA in skin biopsies and peripheral blood mononuclear cells (PBMC) in flea allergic dogs. Objective The aim of our study was to improve the understanding of the immunopathogenesis of allergic dermatitis as a response to fleabites. Material and methods Allergic and non-allergic dogs were exposed to fleas. Before and after 4 days of flea exposure mRNA was isolated from biopsies and PBMC. Production of chymase, tryptase, IL-4, IL-5, IL-13, TNF-α and IFN-γ mRNA was measured by real-time RT-PCR. The inflammatory infiltrate in the skin was scored semi-quantitatively. The number of eosinophils, mast cells (MC) and IgE+ cells/mm 2 was evaluated to complete the picture. Results FAD was associated with a higher number of MC before flea exposure and with a significant increase of eosinophils after flea exposure as compared to non-allergic dogs. The number of IgE+ cells was higher in allergic dogs before and after flea exposure. In allergic dogs mRNA for most cytokines and proteases tested was higher before flea exposure than after flea exposure. After exposure to fleas an increased mRNA production was only observed in non-allergic dogs. In vitro stimulation with flea antigen resulted in a decreased expression of most cytokines in allergic dogs before flea exposure. In contrast, in PBMC, only increased levels of IL-4 and IL-5 mRNA were observed in allergic dogs before flea exposure. However, after flea exposure and additional stimulation with flea antigen the production of mRNA for all cytokines tested was significantly increased in allergic dogs. Conclusion We demonstrated that the response in biopsies and PBMC is different and that FAD is associated with a TH2 response.

Maturing of monocyte derived dentritic cells in the presence of flea antigen extracts in patients with flea-bite induced papular urticaria

RATIONALE: Dendritic cells (DC) are stimulated by recognition of antigens. This study evaluated the capacity of a whole flea extract to induce maturing of monocyte derived dentritic cells in patients with flea-bite antigen papular urticaria and healthy children.

Immune responses to fleas in two rodent species differing in natural prevalence of infestation and diversity of flea assemblages.

We studied in vivo immune response to fleas in two gerbils, Gerbillus dasyurus and Gerbillus andersoni allenbyi, which differed in their natural species richness of flea assemblages and prevalence of infestation. G.dasyurus is parasitized naturally by several flea species, but the prevalence of infestation is low, whereas G. a. allenbyi is parasitized by a single flea species, with high prevalence of infestation. We hypothesized that immunological parameters and the cell-mediated specific immune response to an antigen from an unfamiliar flea species differ between the two gerbil species. Parasitized and control gerbils of both species demonstrated similar, relatively low levels of spontaneous glucose consumption. The same was true for the phytohemagglutinin treatment. Responses to antigen from unfamiliar flea species were higher than both spontaneous glucose consumption and response to phytohemagglutinin in parasitized and control G. a. allenbyi and parasitized G. dasyurus. However, no significant difference in the spontaneous blast transformation index and responses to both phytohemagglutinin and flea antigen was found in control G. dasyurus. The number of white blood cells was significantly lower in control than in parasitized G. dasyurus, whereas no difference in the number of white blood cells was found between control and parasitized G. a. allenbyi. The levels of circulating immune complexes and concentrations of immunoglobulins did not differ between parasitized and control individuals in both species. Phagocytic activity was significantly higher in males than in females of G. a. allenbyi but not of G. dasyurus. In addition, phagocytes of G. dasyurus appeared to be significantly more active than those of G. a. allenbyi.

FC‐35 Real‐time evaluation of cytokine and protease expression in flea‐allergic and nonallergic dogs

Flea bite allergy is a skin disorder with a complex immunopathogenesis. Th2 cytokines and proteases have been hypothesized to play a role in the pathogenesis. The aims of our study were to evaluate the cytokine and protease expression in skin biopsies and peripheral blood mononuclear cells (PBMC), the histopathological response, and the response to intradermal tests (IDT) in sensitized nonallergic and sensitized allergic dogs. Twenty dogs were exposed to fleas once a day for 4 days. Before flea exposure and after the last flea exposure, an IDT was performed, skin biopsies were taken, and PBMC were isolated. Skin biopsies and PBMC were stimulated with various substances, and real‐time RT‐PCR was performed using primers for tryptase, chymase, IL‐4, IL‐5, IL‐13, TNFα and IFNγ. Intradermal tests and histopathological examination of biopsies revealed much stronger reactions in the allergic group. Before flea exposure, mRNA expression of chymase, TNFα, IFNγ, IL‐5 and IL‐13 in biopsies of allergic dogs was higher compared to nonallergic dogs, whereas in PBMC only the expression of IFNγ was higher. After flea exposure, the difference in mRNA expression between allergic and nonallergic dogs was not as striking. In allergic dogs, stimulation of PBMC with flea antigen resulted in a higher expression of IL‐4 and IL‐13, whereas in biopsies only the expression of IL‐4 was higher. Our results demonstrate that even without the presence of antigen, the pattern of cytokine expression differs between allergic and nonallergic dogs. Furthermore, these results clearly demonstrate that the inflammatory response is much stronger in allergic dogs. Funding: Novartis SA.

Flea Bite Hypersensitivity: New Aspects On The Involvement Of Mast Cells

A study was performed to test the effect of sensitization to flea antigen, followed by exposure to fleas on mast cells (MCs), their subtypes, and IgE+ cells. Biopsies were taken from flea-sensitized dogs ( n=28) and non-sensitized dogs ( n=5) that had been exposed to fleas. Control groups consisted of flea-sensitized ( n=12) and non-sensitized dogs ( n=9) that were not exposed to fleas. Biopsies, taken before, 24 and 72 h after local flea exposure, were stained with haematoxylin and eosin (H&E), toluidine blue, a double labelling technique for MC chymase and tryptase and anti-IgE. An intradermal test for flea antigen was performed and serum titres of allergen-specific IgE and IgG were measured. Significantly higher numbers ( P<0.001) of double labelled MCs compared to toluidine blue stained MCs were detectable in flea-sensitized dogs independent of flea exposure. In contrast, in non-sensitized dogs, the number of toluidine blue stained MCs and the number of double labelled MCs did not differ. In flea-sensitized dogs after flea exposure the percentage of C-MC was significantly increased at day 1 ( P<0.001) and day 3 ( P<0.001), whereas the percentage of TC-MCs decreased significantly at day 1 ( P<0.001) and day 3 ( P<0.05). The percentage of T-MCs decreased ( P<0.05 day 0 versus day 1; P<0.05 day 0 versus day 3). No significant difference was detectable after toluidine blue staining and staining for IgE+ cells between the groups nor between the MC density and the number of IgE+ cells. All flea-sensitized dogs had positive skin tests to flea antigen and high serum titres of flea-specific serum IgE and IgG antibodies. In non-sensitized dogs, these results were negative. Our data provide strong evidence for an upregulation of MC proteases during the process of sensitization and a generalized selective release of mast cell tryptase after exposure to the antigen.

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

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.

Induction of feline flea allergy dermatitis and the incidence and histopathological characteristics of concurrent indolent lip ulcers.

The objectives of this study were to characterize the role of intermittent vs. continual flea exposure in the development of flea allergy dermatitis (FAD) in cats, assess the accuracy of intradermal skin testing (IDST) and in vitro testing, and document the incidence and histopathological features of indolent lip ulcers. Ten flea-naive cats were divided into two groups. One group received intermittent flea exposure for 120 days. Thereafter, both groups of cats received continuous flea exposure for 120 days. In vitro testing for flea salivary antibody and IDST utilizing both whole flea antigen and flea salivary antigen were performed. Eight of 10 cats developed clinical signs of FAD within 3 months and five of these eight cats developed lip ulcers which where characterized histopathologically by ulceration with predominantly neutrophilic inflammation and surface bacterial colonization. There was no association between the presence or absence of clinical signs and positive IDST or in vitro results, and no difference in the development of clinical signs was noted between the two groups of cats.

Immediate intradermal flea antigen reactivity in clinically normal adult dogs from south Florida, USA.

Eighty-six clinically normal adult dogs from southern Florida, USA, with no history of dermatitis, were intradermally skin tested with Greer flea antigen 1:1000 w/v to determine the prevalence of positive immediate intradermal reactivity. This study describes the test group of animals and reports the prevalence of sensitivity to the Greer whole-body flea antigen in normal dogs living in a flea-rich environment. Similar to previous research, the highest prevalence of reactivity to flea antigen occurred at 3-4 years of age. The results indicate that 24% of clinically normal dogs from a flea-rich environment exhibited positive immediate skin test reactivity. These dogs had no clinical signs of flea allergic dermatitis (FAD) in spite of ongoing flea exposure. A 2-year follow-up telephone call to the owners of these flea antigen intradermal skin test (IDST)-positive dogs indicated that only two of 21 dogs had developed clinical signs of FAD.

Clinical and histological evaluation of immediate and delayed flea antigen intradermal skin test and flea bite sites in normal and flea-allergic cats.

Seven cats diagnosed as flea allergic by specific criteria and seven normal control cats were exposed to flea bites in a controlled manner and were given intradermal injections of 1:1000 w/v flea antigen. Subjective evaluation of gross lesions and documentation of histological changes at flea antigen intradermal skin test (IDST) and flea bite sites were performed at 15 min, 24 h and 48 h after IDST or flea exposure. Control cats did not develop an immediate gross reaction to either flea bites or the intradermal injection of flea antigen. All seven flea-allergic cats had an immediate gross reaction at the site of IDST with flea antigen; five of these cats also developed immediate gross reactions to flea bites. Three of seven flea-allergic cats developed a gross 24 h and/or 48 h delayed reaction at the flea antigen IDST sites. These three and one other cat had both an immediate and delayed gross reaction to flea bites. Histological examination of 15 min skin specimens from IDST and flea bite sites of flea-allergic cats were similar with a mild lymphocytic, histiocytic and mastocytic superficial perivascular dermatitis. Histological examination of 24 h and 48 h skin specimens from IDST and flea bite sites of flea-allergic cats showed that they were often indistinguishable. Histological features of IDST and flea bite sites of flea-allergic cats at 24 h consisted of a perivascular to diffuse predominately eosinophilic dermatitis and mural folliculitis with variable epidermal necrosis and ulceration.

Allergenic cross-reactivities in flea-reactive canine serum samples

Abstract Objectives To determine whether flea extract could be determined (via ELISA) to share allergenic epitopes with other insects, and to determine whether sera with different reactivities to insect extracts have different cross-reactivity patterns. Sample Population 69 canine serum samples that were selected from samples submitted for routine ELISA allergy testing and had previously been found to have high reactivities to flea. Procedure Each serum sample was assessed by means of a direct ELISA for IgE binding to 11 common insects. Samples that were reactive primarily to flea extract alone were designated pool 1, samples that were reactive to small numbers of insects were designated pool 2, and samples that were reactive to all or almost all insects were designated pool 3. Samples that did not have any apparent patterns of cross-reactivity were not included in the rest of the study. Inhibition ELISA techniques were used with the 3 serum pools to determine whether multiple insect extracts inhibited reactivity on flea-coated ELISA plates. Those extracts were used to coat ELISA plates, and reciprocal inhibition studies were then performed. Results Black fly, black ant, and cockroach extracts were capable of &gt; 50% inhibition of flea solid-phase IgE binding with all 3 serum pools. In the ELISA inhibition studies, flea extract was able to inhibit IgE binding to each extract with all pools, confirming reciprocal inhibition. Conclusions Inhibition of IgE binding to solid-phase flea antigen by black ant, black fly, and cockroach extracts suggested sharing of allergenic epitopes among these species. Reciprocal inhibition studies further confirmed these findings. These results indicated in vitro cross-reactivity between flea, black ant, black fly, and cockroach extracts. These results need to be further investigated in vivo. Clinical Relevance It is possible that dogs may become sensitized to fleas via exposure to other insects, and that flea allergenic dogs may have signs of pruritus, in the absence of fleas, if exposed to cross-reactive insects. (Am J Vet Res 1996;57:1000–1005)

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

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.

Flea allergy dermatitis in dogs diagnosed by intradermal skin tests

Thirty-three dogs were categorised according to their clinical signs of flea allergy dermatitis and reactivity to feeding fleas ( Ctenocephalides felis felis). A soluble extract of whole fleas ( fs), fractions of this extract separated by chromatography, and a commercially available flea antigen extract were used in intradermal skin tests ( idst) to establish the presence or absence of type I and type IV hypersensitivity. The reactions were measured and the results were analysed using three grading systems commonly reported in the literature. The results of the idst for the groups of dogs varied according to the grading system used. fs, the most effective of the antigen preparations, identified 94 per cent of dogs which reacted to feeding fleas when a result was considered positive if the mean diameter of the wheal at the antigen injection site exceeded the diameter of the wheal at the negative control site by five mm at 15 and/or 30 minutes after injection.