Feline atopy in three littermates

Feline allergic diseases: introduction and proposed nomenclature

BACKGROUND

Feline allergic diseases present as challenging problems for clinicians, not least because of the number of reaction patterns of the feline skin, none of which are specific for allergy. Furthermore, there is some controversy over the nomenclature that should be used in their description.

OBJECTIVES

To review the literature, assess the status of knowledge of the topic and the extent to which these diseases could be categorized as atopic in nature, and make recommendations concerning nomenclature.

METHODS

Atopic diseases in humans and cats were researched. A comparison then was made of the essential features in the two species.

RESULTS

There were sufficient similarities between human atopic diseases and the manifestations of feline diseases of presumed allergic aetiology to justify the use of "atopic" to describe some of the feline conditions affecting the skin, respiratory and gastrointestinal tract. However, none of the allergic skin diseases showed features consistent with atopic dermatitis as described in man and the dog.

CONCLUSIONS AND CLINICAL IMPORTANCE

The term "Feline Atopic Syndrome" (FAS) is proposed to encompass allergic diseases of the skin, gastrointestinal tract and respiratory tract, and "Feline atopic skin syndrome" (FASS) proposed to describe allergic skin disease associated with environmental allergies. We are not aware of any adverse food reactions in cats that are attributable to causes other than immunological reactions against the food itself. We therefore propose an aetiological definition of "Food Allergy" (FA) to describe such cases.

Treatment of the feline atopic syndrome - a systematic review

BACKGROUND

Feline allergic skin disease and asthma occur regularly in small animal practice.

OBJECTIVES

To provide evidence-based recommendations for small animal practitioners on the treatment of feline atopic syndrome (FAS).

METHODS AND MATERIALS

The authors reviewed the literature available before February 2020, prepared a detailed evidence-based literature review and made recommendations based on the evaluated evidence.

RESULTS

Sixty-six papers and abstracts were identified describing treatment interventions for FAS and evaluated to establish treatment recommendations. For many treatment options, the papers were retrospective, open studies or case reports.

CONCLUSION AND CLINICAL RELEVANCE

In this review, there was good evidence for the efficacy of systemic glucocorticoids and ciclosporin, and limited evidence for the efficacy of topical glucocorticoids, oclacitinib and allergen-specific immunotherapy in feline atopic skin syndrome. Evidence pointed to low-to-moderate efficacy for antihistamines, fatty acids and palmitoyl ethanolamide. In feline asthma, there was good evidence for the efficacy of oral and inhaled glucocorticoids, and limited evidence of moderate efficacy for allergen-specific immunotherapy. Evidence supported low-to-moderate efficacy of mesenchymal stem cells, inhaled lidocaine and oclacitinib as treatments for feline asthma. For almost all therapeutic options (with the exception of glucocorticoids and ciclosporin), more randomised controlled trials are needed.

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.

Atopic dermatitis in cats and dogs: a difficult disease for animals and owners

The purpose of this review article is to give an overview of atopic dermatitis in companion animals and of recent developments including knowledge on immunological background, novel treatment options and difficulties in disease management. The prevalence of hypersensitivities seems to be increasing. The pathogenetic mechanisms are not fully understood, yet multiple gene abnormalities and altered immunological processes are involved. In dogs and cats, the diagnosis of atopic dermatitis is based on history, clinical examination and exclusion of other differential diagnoses. Intradermal testing or testing for serum allergen-specific Immunoglobulin E is only used to identify allergens for inclusion in the extract for allergen immunotherapy. Symptomatic therapy includes glucocorticoids, ciclosporin, essential fatty acids and antihistamines. A selective janus kinase 1 inhibitor and a caninized monoclonal interleukin-31 antibody are the newest options for symptomatic treatment, although longterm effects still need to be assessed. The chronic and often severe nature of the disease, the costly diagnostic workup, frequent clinical flares and lifelong treatment are challenging for owners, pets and veterinarians. Patience and excellent communication skills are needed to achieve a good owner compliance and satisfactory clinical outcome for the animal.

Gender aspects in allergies of pets - A secondary publication and update

Allergies need not only affect humans; this multifactorial and complex disease can also affect animals. Comparative allergology investigates the many similarities between the pathogenesis, clinics, diagnosis, and therapy of the disorders in humans and pet animals. In contrast to human allergy research, the veterinary field lacks access to a central database, which means there are no cohort studies published. This limits not only the research on breed and regional differences in allergies, but also further studies on the impact of gender in allergies of domestic animals. Moreover, domestic cats, dogs and male horses are castrated in most cases, which neutralises any effects of sexual hormones. In this review article a few interesting findings regarding gender aspects in companion animals were extracted from current literature. In summary, there is a lack of data on gender effects on allergies in cats, dogs or horses.

Cutaneous Hypersensitivity Dermatoses in the Feline Patient: A Review of Allergic Skin Disease in Cats

Feline allergic skin disease presents a unique set of challenges to the veterinary practitioner. Although there is some similarity to what is seen in the allergic canine patient, cutaneous hypersensitivity dermatoses in cats can manifest with strikingly different clinical signs, treatment options and outcomes, and secondary complications/disease entities. Additionally, less is known about the pathogenesis of feline allergic skin diseases, particularly "feline atopic syndrome" when compared to dogs or people. This article aims to review what is currently known in regards to allergic skin disease in the feline patient, with focus on non-flea, non-food hypersensitivity dermatitis.

Characterization of the cutaneous mycobiota in healthy and allergic cats using next generation sequencing

BACKGROUND

Next generation sequencing (NGS) studies have demonstrated a diverse skin-associated microbiota and microbial dysbiosis associated with atopic dermatitis in people and in dogs. The skin of cats has yet to be investigated using NGS techniques.

HYPOTHESIS/OBJECTIVES

We hypothesized that the fungal microbiota of healthy feline skin would be similar to that of dogs, with a predominance of environmental fungi, and that fungal dysbiosis would be present on the skin of allergic cats.

ANIMALS

Eleven healthy cats and nine cats diagnosed with one or more cutaneous hypersensitivity disorders, including flea bite, food-induced and nonflea nonfood-induced hypersensitivity.

METHODS

Healthy cats were sampled at twelve body sites and allergic cats at six sites. DNA was isolated and Illumina sequencing was performed targeting the internal transcribed spacer region of fungi. Sequences were processed using the bioinformatics software QIIME.

RESULTS

The most abundant fungal sequences from the skin of all cats were classified as Cladosporium and Alternaria. The mucosal sites, including nostril, conjunctiva and reproductive tracts, had the fewest number of fungi, whereas the pre-aural space had the most. Allergic feline skin had significantly greater amounts of Agaricomycetes and Sordariomycetes, and significantly less Epicoccum compared to healthy feline skin.

CONCLUSIONS

The skin of healthy cats appears to have a more diverse fungal microbiota compared to previous studies, and a fungal dysbiosis is noted in the skin of allergic cats. Future studies assessing the temporal stability of the skin microbiota in cats will be useful in determining whether the microbiota sequenced using NGS are colonizers or transient microbes.

Feline non-flea induced hypersensitivity dermatitis: clinical features, diagnosis and treatment

PRACTICAL RELEVANCE

Hypersensitivity dermatitis (HD) is often suspected in cats and is mostly caused by insect bites, food or environmental allergens. Cats with non-flea induced HD are reported to present frequently with one or more of the following cutaneous reaction patterns: miliary dermatitis, eosinophilic dermatitis, self-induced symmetrical alopecia or head and neck excoriations/pruritus.

CLINICAL CHALLENGES

None of the above patterns are, however, pathognomonic for non-flea induced HD and the diagnosis of this condition is based on exclusion of diseases presenting similarly and an adequate response to treatment. Therapeutic approaches to affected cats include use of immunomodulatory drugs (ciclosporin, glucocorticoids, antihistamines), hypoallergenic diets and allergen-specific immunotherapy.

EVIDENCE BASE

This review provides an update on the clinical signs, diagnosis and treatment of feline non-flea induced HD. It draws on the findings of a recent large-scale study that described the clinical signs of numerous cats with non-flea HD and has proposed criteria to facilitate the diagnosis of the condition.

A study for characterization of IgE-mediated cutaneous immediate and late-phase reactions in non-allergic domestic cats

Immunoglobulin-E (IgE) mediated reactions can be induced by intradermal injection of anti-IgE antibodies in both humans and dogs. These reactions grossly and histologically mimic changes seen in naturally occurring allergic dermatitis in these species. Similar studies have not been conducted in the cat. Purified polyclonal rabbit-origin IgG specific for canine IgE (anti-IgE) and rabbit immunoglobulin G (IgG) were injected intradermally in 7 non-allergic laboratory colony cats. Wheal measurements were obtained and biopsies collected before injection and at injection sites after 20 min, 6, 24, and 48 h. Injection of anti-IgE induced an immediate wheal response which was significantly larger than that seen after injection of rabbit IgG. Anti-IgE injected skin was also significantly thicker than IgG-injected skin. This corresponded with a significant increase in number of visibly degranulated mast cells in anti-IgE samples when compared to IgG samples. Injection of anti-IgE was associated with the rapid recruitment of inflammatory cells to the injected dermis. The number of inflammatory cells and mononuclear cells were significantly elevated after the injection of anti-IgE when compared to IgG-injected skin. Both eosinophils and neutrophils were significantly increased in anti-IgE samples relative to IgG, although neutrophils were only transiently increased. The high eosinophil and relatively low neutrophil cell counts in these samples were consistent with previously documented histologic features of naturally occurring feline allergic skin disease. Immunohistochemistry identified a significantly overall increased CD1a(+) cells after the intradermal injection of anti-IgE when compared to IgG and non-injected skin. CD3(+), CD8(+) and CD4(+) were also significantly increased overall in anti-IgE injected skin relative to IgG injected skin. These data document the gross and cellular response to injection of anti-IgE in the skin of healthy, non-allergic cats and support a possible role for IgE in the development of feline allergic dermatitis.

Feline superficial pyoderma: a retrospective study of 52 cases (2001-2011)

BACKGROUND

Superficial pyoderma is traditionally considered rare in cats but may be more prevalent than previously reported.

OBJECTIVES

To better characterize superficial pyoderma in cats.

ANIMALS

Fifty-two cats from a dermatology referral population over a 10 year period.

METHODS

This study was retrospective. Cases were included if neutrophils and intracellular bacteria were reported from surface cytology of skin lesions. Medical records were reviewed for signalment, historical and clinical data, cytology results, primary skin diagnoses and treatment details.

RESULTS

Disease prevalence was 20%, with no breed or sex predispositions. The estimated median age of onset was 2 years, affecting 54% of cats by 3 years and 23% after 9 years. Fewer cases presented during winter (15%) compared with other seasons. Skin lesions were typically multifocal, affecting the face (62%), neck (37%), limbs (33%) and ventral abdomen (29%) most commonly. Crusting (83%), alopecia (67%), ulceration/erosion (54%) and erythema (46%) were common lesion types. Pruritus was reported in 92% of cats. Underlying hypersensitivities (confirmed in 60%; suspected in 19%), and atopic dermatitis specifically (confirmed in 48%), were the most frequent primary dermatoses. Cats were treated with a variety of systemic and/or topical antimicrobials. The overall apparent response was considered good in 61% and poor in 27% of cats. Recurrence was confirmed or suspected in 42% of cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

Feline superficial pyoderma was more prevalent in this study population than previously reported. Young cats with hypersensitivities and older cats were more commonly affected, and a variety of lesion types and distributions occurred.

Feline-specific serum total IgE quantitation in normal, asthmatic and parasitized cats

Immunoglobulin E (IgE) plays an important role in defense against parasitic infections as well as allergy. Knowledge of serum total IgE concentrations may have value in diagnosis and prognostication of various disorders; however, to date, no studies have reported feline serum total IgE concentrations. We hypothesize that serum total IgE concentrations will be greater in spontaneously parasitized and asthmatic cats compared to healthy pet cats. Healthy (n=10), parasitized (10) and asthmatic cats (eight) had measurement of serum total IgE by ELISA. Data were analyzed using a t-test with P<0.05 considered significant. Serum total IgE was higher in parasitized (mean±SEM, 328.4±123.8μg/ml; P<0.028) and asthmatic cats (85.5±19.5μg/ml; P<0.047) compared to healthy cats (45.9±19.6μg/ml). However, serum total IgE had poor discriminatory capability between diseased and healthy cats. In conclusion, this assay can detect small quantities of feline serum total IgE, which may be beneficial in future studies of parasitism or allergic disease.

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.

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.

USE OF HYPOSENSITIZATION INJECTIONS TO CONTROL SEASONAL PRURITUS IN A BACTRIAN CAMEL (CAMELUS BACTRIANUS)

A 9-yr-old, female Bactrian camel (Camelus bactrianus) developed severe pruritus in June 1993. During the next 8 yr, the camel exhibited annual episodes of pruritus and epiphora, generally beginning in June and subsiding in October of each year. These signs could usually be controlled with topical agents and fly repellents, although pruritus flare-ups were effectively controlled with intermittent injections of diphenhydramine and corticosteroids. There were no signs during the colder months. The pruritus became more severe and difficult to control when the camel reached its 18th year. Histopathologic descriptions of skin biopsies taken from several sites suggested a hypersensitivity reaction with secondary changes because of bacterial infection or corticosteroid administration (or both). An intradermal test (IDT) performed using 62 allergens regionalized to Northern California resulted in 17 positive test sites. Hyposensitization therapy was initiated using allergens chosen on the basis of exposure, availability, and the results of the IDT, using standard protocols. The clinical signs of pruritus were markedly reduced in the 2 yr after the hyposensitization injections were initiated.

Immunophenotyping of the cutaneous cellular infiltrate after atopy patch testing in cats with atopic dermatitis

Cats with spontaneously occurring atopic dermatitis have clinical and immunocytochemical characteristics compatible with these in humans with atopic dermatitis (AD). The atopy patch test (APT) has proven to be a valuable tool in elucidating the disease process in humans. Additionally, the APT is very specific and bypasses the problem of conflicting results due to differences in chronicity of lesions of AD patients. We adapted the APT for use in cats to explore the suitability of the APT as a tool to study the onset of allergic inflammation in cats with atopic dermatitis. APT were performed in AD cats (n = 6) and healthy cats (n = 10). All cats were patch tested with two allergens in three different dilutions and a diluent control. The allergens for the APT were selected from positive intradermal test and /or prick test results and consisted of: Dermatophagoides farinae, D. pteronyssinus, Tyrophagus putrescentiae, and a grass pollen mixture. APT were read after 10, 24 and 48 h, and punch biopsies for immunohistochemical evaluation were collected at these time points. Macroscopically positive APT reactions were observed in three out of six cats at 24 and/or 48 h with allergen concentrations of 25,000 and 100,000 NU/ml. Reactions were not observed at negative control sites and neither in control animals. A significantly increased number of IL-4+, CD4+, CD3+, MHC class II+ and CD1a+ cells was found in one AD cat with positive APT reactions. Five out of six AD cats had significantly increased IL-4+ T cell numbers at 24 and/or 48 h. Our data indicate that in cats, macroscopically positive patch test reactions can be induced, which have a cellular infiltrate similar to that in lesional skin. We found a high specificity and a macroscopically positive APT reaction in half of the cats, which is similar to what is seen in humans. Hence, the APT in cats might be a useful tool in studying the immunopathogenesis of feline atopic dermatitis.

Mast Cells and Eosinophils in Feline Allergic Dermatitis: A Qualitative and Quantitative Analysis

Mast cells (MCs) and eosinophils are prominent in the perivascular infiltrate of cats with allergic dermatitis. In the skin of allergic cats MCs were mainly observed diffusely in the superficial dermis, while eosinophils were found mainly in the deep dermis in a perivascular pattern. MC counts were significantly higher in cats with allergic dermatitis (P < 0.05) than in healthy control cats, but the number varied widely. Moreover, the numbers of eosinophils in the skin of allergic and control cats differed significantly (P < 0.05) none being found in the latter. There was no significant correlation between numbers of mast cells and eosinophils in the same biopsy sample. In the allergic cats, a significantly lower number of MCs was detected by staining for tryptase than by staining for chymase or by Astra blue staining. Additionally, the chymase: tryptase ratio in healthy cats was reversed in cats with allergic dermatitis. These changes were observed in lesional and nonlesional skin of cats with allergic dermatitis. The findings indicate a generalized effect on MCs in allergic dermatitis. In addition, eosinophils are an important indicator of allergic dermatitis.