Allergy Testing for Skin Disease in the Cat In Vivo vs In Vitro Tests

Comparison of intradermal and serum testing for environmental allergen-specific immunoglobulin E determination in a laboratory colony of cats with naturally acquired atopic syndrome

BACKGROUND

Allergen testing is used to select antigens included in the desensitisation vaccine. Intradermal skin test (IDT) is the gold standard in cats, yet allergen-specific immunoglobulin (Ig)E serological testing (ASIS) is often used. Feline data are lacking regarding the agreement between IDT and ASIS results.

HYPOTHESIS/OBJECTIVES

The first objective of the study was to establish a colony of cats with naturally acquired feline atopic syndrome (FAS). Further objectives were to define their hypersensitivity disorder to detail the allergen tests results, and to assess similarity between the allergen tests.

ANIMALS

Thirty-five cats with FAS and 10 control cats.

MATERIALS AND METHODS

Enrolled cats went through a five phase-screening and quarantine process before joining the colony. An elimination diet trial was performed on all FAS cats. ASIS and IDT were consecutively performed on all cats under sedation.

RESULTS

Reactions to 34 allergens were compiled for the 45 cats. Global sensitivity and specificity of ASIS were 34.7% and 78.9%, respectively. Only flea (ICC = 0.26, p = 0.040) and Dermatophagoides pteronyssinus (ICC = 0.48, p < 0.001) allergens had a significant intraclass correlation (weak agreement). Two FAS cats had negative tests including one cat with a concomitant food allergy.

CONCLUSIONS AND CLINICAL RELEVANCE

This study depicts the first reported colony of cats with naturally acquired FAS. This is the first feline study to compare and show the poor agreement between allergen tests with a panel of 34 allergens. This colony also harbours two cats with FAS with negative allergen tests. These may represent the first described cats with an intrinsic form of atopic syndrome.

Reactions to environmental allergens in cats with feline lower airway disease

Objectives

Aeroallergens have been discussed as potential triggers for feline asthma (FA), which can be induced experimentally by allergen sensitization. To date, only few studies have investigated reactions to environmental allergens in cats with naturally occurring feline lower airway disease (FLAD). The aim of the study was to compare results of intradermal testing (IDT) and serum allergen-specific immunoglobulin E-(IgE) testing (SAT) in cats with FLAD, and to investigate possible associations with allergen exposure.

Material and methods

Eight cats with eosinophilic airway inflammation (EI), ten cats with mixed inflammation (MI), six with neutrophilic inflammation (NI), and 24 healthy cats (HC) were included. Cats diagnosed with FLAD were assigned to the different inflammatory groups based on bronchoalveolar lavage fluid (BLAF) cytology. SAT was performed in all cats; IDT was only carried out in cats with FLAD. Information about the cats' environment and potential allergen exposure was obtained using an owner questionnaire.

Results

In comparison to 83% of HC with positive reactions on SAT only 52% of cats with FLAD had positive responses (p = 0.051). Significantly more positive reactions per cat were detected on IDT than on SAT (p = 0.001). No significant difference was found for positive reactions per cat on SAT when compared between HC, NI, EI, and MI (p = 0.377). Only "slight" agreement was found for most allergens when reactions obtained in both tests in cats with FLAD were compared, except for "moderate" agreement for English plantain (k = 0.504) and Alternaria alternata (k = 0.488). Overall, no clear association between the cats' environment and allergen reactions were detected.

Conclusions and clinical importance

Interpretation of allergy test results in cats with FLAD should be done in the context of clinical signs and individual factors.

Intradermal testing and serum allergen-specific IgE-testing in cats with naturally occurring feline bronchial disease

OBJECTIVES

While feline asthma (FA) is considered to be of allergic origin, the etiology of feline chronic bronchitis (CB) to date is unknown. Aim of the study was to compare the results of intradermal testing (IDT) and serum testing for allergen-specific immunoglobulin E (SAT) in cats diagnosed with FA and CB.

MATERIAL AND METHODS

Twenty-seven client-owned cats with clinical signs, suggestive of feline inflammatory bronchial disease (FBD) were prospectively enrolled in the study. Patients were assigned to 3 groups based on results of bronchoalveolar-lavage-fluid (BALF)-cytology: FA (n=8), CB (n=10), or cats with a physiological BALF cytology (PB; n=9). A standardized IDT for 27 allergens was performed in all cats. In addition, allergen-specific IgE was measured in serum samples using an FcεRIα-ELISA. The number of positive reactions in both tests was compared between groups, and agreement between test results of both tests was evaluated.

RESULTS

Regarding the number of positive reactions, no statistically significant difference was detected between groups in IDT (p=0.65) and SAT (p=0.51). When comparing the 2 test systems, a weak correlation was found for the allergens Tyrophagus putrescentiae (k=0.256), Dermatophagoides farinae (k=0.276), and rye (k=0.273). The most commonly observed reactions were to house dust mites, storage mites, rye and nettle in IDT and to sheep sorrel, storage mites, and house dust mites in SAT.

CONCLUSION AND RELEVANCE

IDT and SAT in cats with feline inflammatory bronchial disease (FBD) cannot be used interchangeably for allergen detection. Sensitization to environmental allergens can occur in cats with and without airway inflammation. Therefore, a positive test result should always be assessed in context with clinical signs and allergen exposure.

Feline heartworm disease and environmental allergens hypersensitivity: is there a link?

BACKGROUND

Cats can be infected by Dirofilaria immitis, the causative agent of heartworm disease, characterized by respiratory signs, airway hyperreactivity, remodelling and inflammation. Allergy is a multifactorial pathology, and the role of a number of helminth parasites in the development of allergies in humans and other species has been demonstrated in many studies. The aim of the present study was to verify whether cats seropositive for D. immitis present hypersensitivity to some environmental allergens.

METHODS

Blood samples were collected from 120 cats and tested for the presence of specific immunoglobulin G antibodies against D. immitis and for hypersensitivity to 20 allergens, using commercial allergen test kits.

RESULTS

Of the 120 cats tested, 72 (60.0%) were seropositive for anti-D. immitis IgG and 55 (45.8%) showed clinical signs of heartworm disease of a respiratory nature. The results of testing with the allergen kits showed that 50.8% of cats were seropositive for ≥ 1 allergens, with the most common allergens being Dermatophagoides farinae (25.8%), Dermatophagoides pteronyssinus (20.0%), Malassezia (17.5%) and Ctenocephalides felis (14.2%). The prevalence of allergies was significantly higher-by almost threefold-in cats seropositive for D. immitis (68.1% vs. 25%). There were no significant differences between the prevalence of allergic cats and presence/absence of symptoms, and the results confirmed that symptoms were not a decisive factor for the presence of allergies. The risk for developing allergies was 6.3-fold higher in cats seropositive for D. immitis than in cats that were seronegative, confirming that seropositivity for D. immitis is a risk factor.

CONCLUSIONS

Cats with confirmed heartworm can develop serious respiratory signs, potentially leading to progression to permanent lung injury and predisposing cats to hyperresponsive airway disease. Previous studies have shown that seropositivity for D. immitis and Wolbachia is related to the presence of bronchoconstriction and bronchospasm in the affected cat. The results support the suspicion that contact with D. immitis may be a risk factor for the presence of allergies.

Immunopathogenesis of the feline atopic syndrome

BACKGROUND

Feline diseases of possible allergic origin with similar clinical phenotypes can have a varied underlying pathogenesis. Clinical phenotype, precise aetiology and underlying immunopathogenesis all need to be considered if advances in this neglected area of dermatology are to be made.

OBJECTIVES

To document the status of research into the immunopathogenesis of the diseases that fall within the spectrum of the feline atopic syndrome (FAS ), to summarize the conclusions, identify the limitations and recommend future research directions.

METHODS AND MATERIALS

A search of the literature was undertaken. The strengths and validity of the data and the contributions to our current understanding of the immunopathogenesis were analysed. Skin diseases of presumed allergic aetiology and asthma were assessed separately, as was the role of antibodies, cells and cytokines in each.

RESULTS

The research varied in its quality and its impact often was limited by a failure to employ strict criteria in case selection. This reflected the difficulties of skin reaction patterns associated with a number of inciting causes. Research into feline asthma was handicapped by the difficulties of investigating clinical material, and much of the useful information was derived from experimental models.

CONCLUSIONS AND CLINICAL IMPORTANCE

The evidence reviewed was supportive of a role for immunoglobulin (Ig)E in the pathogenesis of both feline atopic skin syndrome (FASS) and asthma, albeit not strongly so. The inflammation noted in both FASS and asthma is accompanied by eosinophils and lymphocytes, and these findings, together with the cytokine expression, are suggestive in some (not all) cats of T-helper type 2 immune dysregulation.

Clinical signs and diagnosis of feline atopic syndrome: detailed guidelines for a correct diagnosis

BACKGROUND

Feline atopic syndrome (FAS) describes a spectrum of hypersensitivity disorders characterised by highly diverse clinical presentations including skin, gastrointestinal and respiratory systems. Among these disorders is feline atopic skin syndrome (FASS), in which hypersensitivity is typically associated with environmental allergens, although food allergy may coexist. Involvement of other organ systems (e.g. asthma) also may occur. Because of its highly heterogeneous clinical presentation, diagnosis of FASS can be challenging.

OBJECTIVES

A subgroup of the International Committee on Allergic Diseases of Animals was tasked to summarise the most current information on the clinical presentations of FASS and to develop diagnostic guidelines.

METHODS AND MATERIALS

Online citation databases and abstracts from international meetings were searched for publications related to feline allergic conditions. These were combined with expert opinion where necessary.

RESULTS

A total of 107 publications relevant to this review were identified. Compilation of these data enabled development of a detailed description of the clinical features of FASS and development of guidelines focusing on systematic elimination of other skin conditions with similar clinical characteristics. As allergen tests are frequently used by dermatologists to support a clinical diagnosis of FASS, a brief review of these methodologies was also performed.

CONCLUSIONS AND CLINICAL IMPORTANCE

In a similar way to atopic dermatitis in dogs, FASS is a clinical diagnosis based on the presence of compatible clinical signs and exclusion of other diseases with similar clinical features. Elimination or exclusion of fleas/flea allergy, other parasites, infections and food allergy is mandatory before reaching a diagnosis of FASS.

Lymphocyte blastogenic responses to food antigens in cats showing clinical symptoms of food hypersensitivity

Three cats were diagnosed as having food hypersensitivity by food elimination and oral food provocation tests. Twelve allergenic food ingredients were identified by oral food provocation test in the 3 cats. Of the 12 food ingredients, 9 offending food antigens were shown to be positive in a lymphocyte stimulation test; however, none of them were positive in antigen-specific IgE testing, and only four food antigens were positive in intradermal testing. The stimulation indices in the lymphocyte stimulation tests for the 9 food ingredients were found to be decreased after the cats were fed elimination diets. The present study demonstrates that the lymphocyte stimulation test reflects an immunologic reaction involved in food hypersensitivity and can help identify allergenic food ingredients in feline food hypersensitivity.

Comparison of intradermal skin testing (IDST) and serum allergen-specific IgE determination in an experimental model of feline asthma

Intradermal skin testing (IDST) and allergen-specific IgE determination are used to determine allergen sensitization. In cats, studies have found poor correlation between the two tests. However, these studies were mainly conducted in pet cats sensitized to unknown allergens with unknown dose and duration of exposure. We hypothesized that in an experimental model of allergic sensitization where these variables are controlled, IDST would demonstrate greater sensitivity and specificity than would serum allergen-specific IgE determination. A model of feline asthma employing Bermuda grass allergen (BGA) or house dust mite allergen (HDMA) was used to test the hypothesis. Thirteen cats were assigned to undergo sensitization to BGA, HDMA or saline (placebo). Bronchoalveolar lavage fluid confirmed development of an asthmatic phenotype. Serum collection and IDST were performed on D0, D28 and D50. A portion of serum was pooled, and an aliquot heat inactivated (HI) to destroy IgE. Individual, pooled, and pooled HI samples were used for allergen-specific IgE determination using an Fc epsilon R1 alpha-based ELISA; pooled samples were also analyzed using an enzymoimmunometric assay. Sensitivity (SE), specificity (SP), and positive and negative predictive values (PPV and NPV) were calculated for IDST and for BGA- and HDMA-specific IgE. Combined results for IDST found SE=90.9%, SP=86.7%, PPV=83.3%, and NPV=92.9%. For ELISA-based serum IgE testing, the SE=22.7%, SP=100%, PPV=100% and NPV=63.8%. The enzymoimmunometric assay did not detect sensitizing IgE, but did detect IgE reactivity to a variety of irrelevant allergens (even in HI samples). Sensitivity of IDST was greater than sensitivity of serum IgE measurement supporting use as a screening test for aeroallergens. Both IDST and allergen-specific IgE determination via ELISA were specific; either test can be used to guide selection of allergens for immunotherapy. The enzymoimmunometric assay was unreliable and cannot be recommended.

Feline immunoglobulin E: historical perspective, diagnostics and clinical relevance

Immunoglobulin E (IgE) plays a critical role in the immune response to parasitic infections and also mediates pathology in allergic disease. While the role of this antibody in both naturally developing and experimentally induced parasitic and allergic diseases of cats has been recognized for decades, the relatively slow development of reagents specific for feline IgE has hindered studies on clinically important IgE-mediated diseases in the cat. This review highlights the major advances which have been made and discusses the current literature demonstrating the role of IgE in feline parasitic infections and allergy.

Group 1 and 2 Dermatophagoides house dust mite allergens in the microenvironment of cats

House dust mite allergens (HDMAs) are some of the most common allergens associated with allergic diseases in humans and dogs. The purpose of this study was to determine whether HDMAs could be detected in cat-associated household microenvironments. From 50 cat-only households with 95 cats, dust samples were collected by vacuuming for 2 min m(-2) from three areas where cats slept or rested regularly from September to October 2006. Relative humidity and temperature were measured in each household using a data logger. Each owner completed a questionnaire on potential factors that might influence the prevalence of house dust mites (HDMs). Dust samples were analysed utilizing an ELISA for Der p 1, Der f 1 and HDM group 2 allergens. In 38 of 50 households there was greater than 2 microg g(-1) of dust for at least one HDMA. Using stepwise logistic regression, factors associated with increased HDMA levels included: free-standing houses, number of humans in household, longhaired cats and age of the cat. Factors associated with decreased HDMA concentrations included: forced air heating and central air conditioning, less than 50% carpeting of the home, use of flea control, cats suffering from dermatological disease and the average temperature of the household. Many sleeping/resting areas utilized by cats contain sufficiently high levels of HDMAs to be potential sources of sensitization. This finding should lead to further determination of the role of HDMs in cats suffering from putative allergic conditions such as atopic dermatitis or asthma.

A review of allergen-specific immunotherapy in human and veterinary medicine

This article reviews allergen-specific immunotherapy in human and veterinary medicine. Current hypotheses of possible mechanisms of actions are outlined. Indications, success rates, adverse effects and factors influencing outcome of therapy are discussed in humans, dogs, cats and horses.

Prospective open pilot study on the use of ciclosporin for feline allergic skin disease

OBJECTIVES

To evaluate the efficacy of ciclosporin in cats with allergic skin disease.

METHODS

Ten cats with signs of allergic skin disease were administered ciclosporin daily at a dose of 3.6 to 8.3 mg/kg for one month. None of these cats had previously responded to a hypoallergenic diet trial, and all animals had previously been treated with endectoparasiticidal drugs, with no improvement two weeks before entering the trial. On days 0 and 30, owners assessed pruritus with a visual analogue scale, and veterinarians evaluated cutaneous lesions.

RESULTS

All the cats had pruritus and erythema, five had alopecia, two had an eosinophilic plaque, one had miliary dermatitis and two had both alopecia and an eosinophilic plaque. Good or excellent improvement was observed in 40 per cent of cats for pruritus, 57 per cent of cats for alopecia and 60 per cent of cats for erythema. A significant decrease in mean scores was observed for pruritus only, while for erythema and alopecia, it was close to being significant (P < 0.052).

CLINICAL SIGNIFICANCE

Ciclosporin may be helpful in symptomatically treating signs of feline allergic skin disease. However, it is important to remember that ciclosporin is not licensed for use in cats.

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.

The effects of endoparasitism on the immune response to orally administered antigen in cats

The aim of the study was to assess whether infection with Toxocara cati (T. cati) facilitates the induction of immunoglobulin (Ig) E or other antibody responses to a specific antigen administered with food in kittens. Two groups of 10 cats each, either experimentally infected with T. cati or parasite-free, were dosed with human serum albumin (HSA) added daily to their food from day 7 to 28 inclusive. Levels of HSA-specific IgE, IgG, IgA and IgM were assessed in the serum by enzyme-linked immunosorbent assay (ELISA) in both groups of cats at weeks 0, 2, 4 and 8. Although weak, an IgE response was detected in most of the cats 1 week after exposure to HSA. However, HSA-specific IgG and IgA could only be detected from the third week after exposure to HSA. The group of parasitized cats had significantly higher levels of HSA-specific antibodies of the IgG and IgA at weeks 4 and 8 (p<0.05 by Mann-Whitney) and IgE isotypes at weeks 2 and 4 (p<0.05 by analysis of variance (ANOVA)) than did the group of parasite-free cats. Specific IgM antibody was not detected in the sera of any of the 20 cats. These findings are supportive of a role of T. cati infection in enhancing the IgE response to orally administered antigens, and hence possibly, in genetically susceptible individuals, in the development of food hypersensitivity.

Measurement of serum immunoglobulin E (IgE) specific for house dust mite antigens in normal cats and cats with allergic skin disease

The purpose of this study was to determine whether cats with allergic skin disease have significant concentrations of serum Immunoglobulin E (IgE) specific for antigens derived from the house dust mites (HDM) Dermatophagoides farinae (DF) and Dermatophagoides pteronyssinus (DP). Enzyme-linked immunosorbent assays (ELISA) were developed for this purpose. Binding of serum allergen-specific IgE was detected via the use of biotinylated Fc-epsilon receptor alpha chain protein (FcvarepsilonRIalpha). Following optimisation of the assay, serum samples from 59 cats with allergic skin disease and 54 clinically normal cats were screened. Results were expressed as ELISA units per ml (EU/ml) compared to a standard curve. Serological findings were correlated with the clinical presentation of affected cats. Cats with symptoms of feline allergic skin disease were grouped as follows: self-induced alopecia without lesions (group 1), papulocrusting dermatitis (group 2), eosinophilic granuloma complex (group 3), papular/ulcerative dermatitis of head and neck/facial dermatitis (group 4), and a combination of symptoms (group 5). Control normal cats comprised the final group (group 6). The Kruskal-Wallis test was used for statistical analysis. There was no significant difference between groups for DF- and DP-specific IgE concentrations with a p-value of 0.875 and 0.705, respectively. Although the FcvarepsilonRIalpha-based ELISA was able to detect house dust mite-specific feline IgE, the presence of this allergen-specific IgE correlates poorly with the presence of clinical manifestations of allergic skin disease. The results of this study question the clinical relevance of house dust mite-specific IgE in feline allergic skin disease.

Production of polyclonal antisera against feline immunoglobulin E and its use in an ELISA in cats with experimentally induced asthma

Serum samples from six cats with experimentally induced asthma were used to purify feline IgE using gel filtration and affinity chromatography. The resultant IgE, evaluated for purity by immunoelectrophoresis (IEP) and reactivity by Prausnitz-Kustner (PK) testing, was used to develop polyclonal rabbit anti-feline IgE antisera. Using reverse cutaneous anaphylaxis (RCA), the antisera were determined to be specific for feline IgE. The polyclonal rabbit anti-feline IgE antiserum was then validated in an allergen-specific ELISA. Serum samples from an additional five asthmatic cats sensitized with Bermuda grass allergen (BGA) were evaluated prior to sensitization, after parenteral sensitization, and after aerosol sensitization and challenge. A significant increase in serum BGA-specific IgE was noted over time.

Evaluation of skin test reactivity to environmental allergens in healthy cats and cats with atopic dermatitis

OBJECTIVE

To evaluate skin test reactivity to environmental allergens in healthy cats and in cats with atopic dermatitis (AD).

ANIMAL

10 healthy cats and 10 cats with AD.

PROCEDURE

10 allergens in serial dilutions were injected ID on the lateral aspect of the thorax of sedated cats. Histamine (0.01% solution) and buffer solutions were used as positive and negative controls, respectively. Immediately after the last injection, 10% fluorescein solution was administered IV. Skin test results were evaluated with ultraviolet light after 15 to 30 minutes and at 4 and 6 hours by 2 independent observers. In the control group, skin tests were repeated after 6 weeks. Skin test reactivity and the nature of the immunoglobulin involved were investigated by use of the Prausnitz-Küstner test with untreated and heat-treated cat sera.

RESULTS

Intertest and interobserver agreement were high when measurement of the diameter of the fluorescent wheal was used to evaluate skin test responses, compared with assessment of its intensity. In both groups of cats, immediate skin test reactivity was observed as an IgE-mediated reaction, as an IgG-mediated reaction, and as a result of nonspecific mast cell degranulation. There was no correlation between allergen concentration and the type of reaction observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Skin test reactivity in cats should be evaluated after IV administration of 10% fluorescein solution by means of a Prausnitz-Küstner test to differentiate among IgE-mediated, IgG-mediated, and nonspecific reactions.

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.

Feline immunoglobulin E: induction of antigen-specific antibody in normal cats and levels in spontaneously allergic cats

Sera from 10 cats with symptoms consistent with atopy, from 15 normal household cats and from 11 laboratory maintained cats were assessed for allergen-specific IgE and IgG to Dermatophagoides farinae (DF) by enzyme-linked immunosorbent assay (ELISA). In addition, 10 normal cats were immunised with DF and intradermal skin tests (IDST) were performed weekly. Sera from the latter were also assessed for DF-specific IgE by ELISA and using Prausnitz-Küstner (PK) tests. Although DF-specific IgE was detectable in all the atopic cats, there was no significant difference between the levels in this group and in the clinically normal household cats. However levels in both these groups were significantly higher than those in the laboratory maintained cats. Detectable DF-specific IgE was induced in all of the 10 cats, but the levels were not correlated with the development of positive IDSTs, nor with the level of IgE as assessed by PK tests. These findings are consistent with a possible heterogeneity of IgE antibody in cats.

Allergen-specific IgG antibodies in cats with allergic skin disease

An enzyme-linked immunosorbent assay was developed for quantifying feline serum allergen-specific IgG directed against selected house dust, pollen and flea allergens. The assay was used to compare allergen-specific IgG concentrations in sera from healthy cats, cats with non-dermatologic illness, confirmed allergic cats and undiagnosed pruritic cats. Our results demonstrate that cats with confirmed allergic skin disease have significantly more IgG directed against house dust, flea and ryegrass allergens than other cat groups examined. These results support the theory that cats with allergic skin disease have an underlying TH2 lymphocyte response that directs production of both allergen-specific IgG and IgE.

Diagnostic procedures in feline dermatology

No substitute exists for diligence and meticulous care in the performance of these diagnostic procedures. The test results are only as good as the technique used to collect the data.

Focal and generalized alopecia

Focal or generalized alopecia is defined as hair loss affecting the ventral, lateral, perineal, and dorsal aspects of the trunk of the cat, usually in a symmetric pattern. This may be attributable to failure of hair coat production, excess loss of hair due to self trauma, or excess shedding of whole hairs. Self trauma is the most common cause of hair loss and is associated particularly with flea allergy dermatitis. Other causes of hair loss are reviewed.

Selected feline eosinophilic skin diseases

Eosinophilic plaque and mosquito-bite dermatitis are recognized hypersensitivity reactions. The pathogenesis of eosinophilic granuloma and indolent ulcer are not as clearly understood. Each of these syndromes is distinctive from a clinical and histopathologic view point. Accurate diagnosis depends on history, physical findings, and histopathologic evaluation. Understanding of feline dermatology will be furthered by including these syndromes in a broader grouping that encompasses all the feline eosinophilic dermatoses.