Sweet Itch Research Articles

Insect Bite Hypersensitivity in Horses: Causes, Diagnosis, Scoring and New Therapies.

Insect Bite Hypersensitivity (IBH, Queensland itch, sweet itch, equine summer eczema) is the most common pruritic disease of horses. It is most often caused by sensitivity to the saliva of Culicoides spp. of biting midges; however, it can also be caused by hypersensitivity to other insect species. The prevalence of IBH in horses is reported to be as high as 60% in some parts of the world. Due to the severe pruritus and effects of secondary self-trauma, IBH has animal welfare concerns, and there is currently no cure. Management of this condition is life-long, time consuming and costly. New grading systems to document disease severity are being validated, which will allow the comparison of clinical trial results of new and existing therapies. Management involves the minimisation of insect bites by use of stabling, fans, rugs and repellents. Symptomatic therapy involves the administration of systemic or topical corticosteroids, systemic antihistamines, and creams and sprays to promote skin healing and decrease inflammation. New immune-mediated therapeutics including vaccines, in addition to desensitisation procedures, show promise at controlling hypersensitivity reactions. This article will review aetiologic agents, pathophysiology, scoring systems and current and new therapies.

Approaching the future management of sweet itch

Insect bite hypersensitivity, commonly known as the ‘sweet itch’, continues to prove frustrating to manage in practice. Insect bite hypersensitivity is the most common allergic skin disease in horses, characterised as a hypersensitivity to the salivary proteins of the Culicodes genus of insects. The complex nature of this allergic disease means that no set of affected horses can be managed in the same way. Common approaches to sweet itch can be broken down into the categories of anti-inflammatories, allergen avoidance, skin conditioning and immunotherapy. Many effective management techniques focus on avoiding insect bites and regularly washing skin. Advances are currently being made towards effective immunotherapy, with varied results in clinical trials and in practice. As a result of this, a multimodal approach to the management of insect bite hypersensitivity is often recommended.

Mosquito Magnet® traps as a potential means of monitoring blackflies of medical and veterinary importance.

Mosquito Magnet® traps, deployed in widespread parts of England as part of nationwide mosquito surveillance projects, also caught blackflies. As many as 1242 blackflies were caught in a trapping session lasting 4 days. Principal among the species caught were Simulium equinum, Simulium lineatum and Simulium ornatum s.l. As S. ornatum s.l. is a vector that transmits Onchocerca linealis to cattle and S. equinum is responsible for dermatitis ('sweet itch') in cattle and horses, it is suggested that Mosquito Magnet® traps could be used to monitor and partially control these pests, as well as nuisance anthropophilic blackflies such as Simulium posticatum that can cause simuliidosis in southern England.

Get ahead of sweet itch

Stella Chapman BVSc (Hons), MSc, MRCVS describes the etiology and management

Microsporum gypseum-infectie bij een paard met erge zomereczeem

Bij een paard met erge zomereczeem en een voorgeschiedenis van corticosteroïdebehandeling voor deze aandoening, werd een welomschreven, cirkelvormig letsel met witte korstvorming opgemerkt. De geofiele schimmel Microsporum gypseum werd geïsoleerd uit het letsel, waarna een vier weken durende topicale behandeling met enilconazole werd gestart. Twee maanden na de behandeling was het letsel volledig hersteld. Deze case-report laat vermoeden dat zomereczeem in combinatie met systemische corticosteroïdebehandeling als risicofactor kan optreden voor een dermatofyteninfectie. Verder wordt het belang van een correcte staalname, isolatie en identificatie van de oorzakelijke kiem bediscussieerd.

A Pilot Qualitative Investigation of Stakeholders' Experiences and Opinions of Equine Insect Bite Hypersensitivity in England.

Equine insect bite hypersensitivity (IBH), commonly known as sweet itch or summer eczema, is a frustrating recurrent skin disease in the equine industry involving an immune reaction to the bites of Culicoides spp. midges. To investigate the impact of IBH in the field, an exploratory pilot study was conducted with equine stakeholders in one region of central England. Nine semi-structured, face-to-face interviews were conducted with horse owners and an equine veterinarian. The aim was to gain an understanding of experiences with IBH, and to gauge opinions on the value of the various management strategies horse owners use to control IBH. Awareness of IBH was generally high, particularly in those individuals who had previous experience with the condition. Those with previous experience of IBH commented on the significant effect on daily routines, and the associated cost implications. Most participants supported an integrated approach to hypersensitivity management, and this most commonly involved a combination of physical barriers and chemical repellents, but sometimes included feed supplementation. Overall, attitudes towards IBH suggested that the condition is a notable welfare and economic concern for stakeholders, but veterinary involvement tended to only be in more severe cases. Further research is required in the future to improve understanding, management and potential treatment of this condition.

Insect Bite Hypersensitivity (Sweet Itch) in a Non-Descript Riding Local Breed Mare

Insect Bite Hypersensitivity (Sweet Itch) in a Non-Descript Riding Local Breed Mare

The itch that's less than sweet

Redwings' equine veterinary nurse Anna Clarke discusses the problems caused by sweet itch and other seasonal skin irritations

Managing insect bite hypersensitivity in horses

Despite extensive research in recent years into the aetiopathogenesis of sweet itch (more appropriately termed insect bite hypersensitivity or IBH) there have been no revelations in options for treatment. Where new treatments have become available they have not been supported by published evidence of efficacy leaving clinicians uncertain as to their relative merits. The absence of universally effective treatments has left the door open for a plethora of products to line the tack shop shelves frequently leaving the veterinary profession side-lined when it comes to managing the condition. This is regrettable as advice on effective management and avoidance strategies is likely to be infinitely more valuable than any treatments employed after clinical signs have developed.

The big itch

Ed Whittle, MA, VetMB, MRCVS, technical consultant at Elanco Companion Animal Health discusses the perennial trauma of sweet itch

Pruritus – nicht immer ist es ein Sommerekzem

Pruritus is not a disease but a physiological protective alarm system which might react in a pathological destructive fashion, depending on the triggering cause. In horses a frequently suspected reason for destructive pruritus is an allergic disease termed “summer eczema”, “sweet itch”, or “insect bite hypersensitivity”. However, there are numerous alternatives provoking similar clinical symptoms. Additional problems for proper diagnosis and appropriate therapy cause “mixed” forms of diseases: On one hand different causes might occur simultaneously and on the other hand one cause might act via different pathomechanisms. For example: Black flies might provoke strong itching just by their injected saliva when biting (simuliotoxicosis) without any underlying allergy. However, a horse might be allergic against such saliva components. Thus, the intense pruritus is now caused by type I-allergy mechanisms within the framework of a “summer eczema”. This paper compromises two parts. Part 1: Definition and clinical forms of “summer eczema”. Part 2 (to follow in issue 3/2011 of this journal): Pathomechanisms of “summer eczema” including relevant diagnostics plus a list of most of the relevant alternative causes for pruritus and/or “sweet itch”-like symptoms.

Equine insect-related summer skin diseases

Equine summer skin diseases are primarily dominated by insect-related conditions, although outdoor allergens and the sun are responsible for the large proportion of the remaining commonly presented problems. This article reviews the aetiology, presentation and current diagnostic and therapeutic approaches to common insect-induced dermatoses including insect bite hypersensitivity (sweet itch) and harvest mite infestation.

Equine skin affection, prevalence and related risk factors in Egypt

This work aimed to study the prevalence of different skin q[fections in equine and the risk factors influencing it during one year from February 2009 to February 2010. Out of 3014 examined equine, 267 (8.86%) were s4ffering from skin diseases. The prevalence rate was dermatophytosis 3.52%, Sweet itch 2.19%, Mange 1.46%, bac­ terial dermatitis 0.36% , cutaneous pythiosis 0.3%, cutaneous habronemiasis 0.27%, vitiligo 0.2%, allergic dermatitis 0.2%, urticaria 0.17%, tick allergy 0.13% and equine warts 0.07%. Dermatophytosis occurred with high incidence rate in Arabian horses al­ though good hygiene and management comparing to drqft horses which showed spo­ radic cases. The disease occurred more commonly in younger ages and infall season. The mycotic cultivation revealed 75 dermatophyte isolates. The most common isolated dermatophyte was T.equinum 53.3%followed by M.canis 29.3% and other dermatoph­ ytes were isolated as M.gypseum 9.3%, T.mentagrophytes 5.3%, T.tonsurans 1.3% and M.audouinii 1.3%. Sweet itch occurred with higher incidence in horses at summer sea­ son and the number of horses q[fected with sweet itch rose with increasing age. Mange was diagnosed mostly in draft horses and donkeys with high incidence in win­ ter. No age difference was observed in the occurrence of mange in equine. Psoroptic mange was the most common cause of mange in equine

Homeopathic prescribing for chronic conditions in equine veterinary practice in the UK

Twelve Faculty of Homeopathy veterinarians recorded data systematically at 777 consecutive homeopathic appointments for horses over a period of 12 months. A spreadsheet enabled the recording of information, which included...

Variations in the concentration of zinc in the blood of Icelandic horses

The effect of factors including the horses’ farm environment, their sex and age and whether they suffered from summer seasonal recurrent dermatitis (sweet itch) on the concentrations of zinc in...

Protein kinase C (PKC) isotype profile in eosinophils from ponies with sweet itch and role in histamine-induced eosinophil activation

Eosinophils have been implicated in the pathogenesis of the seasonal equine allergic skin disease, sweet itch. Protein kinase C (PKC) is involved in regulating eosinophil function and antigen challenge has been reported to alter PKC isotype expression in blood eosinophils from allergic human subjects. Here we have compared the pattern of PKC isotype expression in eosinophils from sweet itch ponies with that in cells from normal ponies both during the active and inactive phases of the disease. A role for PKC in histamine-induced eosinophil activation was also investigated. Conventional PKCs α and β, novel PKCs δ and ε and atypical PKCs ι and ζ were identified in eosinophils pooled from four allergic ponies during the inactive phase, when no clinical signs were evident. The PKC isotypes, like those in eosinophils from normal ponies, were located primarily in the particulate fraction of the cell. Isotype expression in cells from normal and allergic animals did not appear to be different. In contrast, during the active phase of the disease, when the sweet itch ponies had clinical signs, the expression of PKCs β, ε and ι in eosinophils from these animals appeared to be increased relative to that in cells from normal ponies. When PKC expression in eosinophils from five individual normal and sweet itch ponies was compared, small, but statistically significant, increases in PKCε and PKCδ expression were evident in eosinophils from the sweet itch ponies during the active and inactive phases, respectively. The non-selective PKC inhibitors, staurosporine and Ro31-8220, significantly reduced histamine-induced superoxide production. Use of Gö6976, an inhibitor of conventional PKCs, suggested that PKCα and/or β were involved and that there was significantly greater inhibition of the response in eosinophils obtained from sweet itch ponies during the active phase. There was no significant difference in histamine-induced superoxide production by eosinophils from allergic and normal ponies and the functional significance of the increased PKC isotype expression in eosinophils from sweet itch ponies relative to that in cells from healthy animals remains to be established.

Role of the chemokine eotaxin in the pathogenesis of equine sweet itch

The chemokine eotaxin is involved in the recruitment of eosinophils and T helper 2 lymphocytes in human allergic diseases, and drugs that block its activity, including eotaxin receptor (CCR3) antagonists,...

Detection of IgG and IgE serum antibodies to Culicoides salivary gland antigens in horses with insect dermal hypersensitivity (sweet itch).

We postulated that all horses exposed to the bites of Culcoides (midges) would have an antibody response to the antigen secreted in Culcoides saliva, but that IgE antibody would be restricted to allergic individuals. Using immunohistology on sections of fixed Culicoides, we have demonstrated the presence of antibodies in horse serum which recognise Culicoides salivary glands. Antibodies were detected in the serum of horses with insect dermal hypersensitivity and in the serum of normal horses exposed to Culicoides bites. In contrast, no antibodies were detected in serum from native Icelandic ponies which had not been exposed to Culicoides. Anti-salivary gland IgG antibodies were detected in serum from both allergic and healthy horses exposed to Culicoides. IgE antibodies were only detected in horses with signs of insect dermal hypersensitivity, they were not found in serum of healthy controls nor in the serum of horses with a history of hypersensitivity but in remission at the time of sampling. Using western blotting we confirmed the presence of antibodies to Culicoides antigens and demonstrated that individual horses react to different numbers of antigens. This paper demonstrates the ability of serum from allergic horses to detect Culcoides antigens and will enable further studies to isolate and characterise the allergens.

Culicoides antigen extract stimulates equine blood mononuclear (BMN) cell proliferation and the release of eosinophil adherence-inducing factor(s)

Intradermal injection of a Culicoides antigen extract (CAgX) induces T lymphocyte and eosinophil accumulation in the skin of horses with sweet itch. Blood mononuclear (BMN) cells from normal ponies proliferate when stimulated by mitogen (phytohaemagglutinin, PHA) or antigen (tetanus toxoid, TT) and, as shown here, release soluble factor(s) that induce eosinophil adherence. CAgX also caused concentration dependent proliferation ofBMN cells from sweet itch and normal ponies [stimulation index: 29 (13) and 17 (7) for BMN cells from sweet itch and normal ponies, respectively during the active phase of disease; 4 μg protein ml−1CAgX; 168 h]. A heat labile factor(s) which caused eosinophil adherence was also released [sweet itch ponies: 6.0 (1.6) per cent adherence versus 1.3 (0.4) per cent; normal ponies: 6.6 (0.5) per cent adherence versus 0.9 (0.1) per cent for supernatants from CAgX (4 μg protein ml−1; 48 hours) stimulated versus unstimulated BMN cells, respectively]. These results suggest that soluble proteins released from T lymphocytes could affect eosinophil function in the lesional skin of sweet itch horses.

Differential activation of platelets from normal and allergic ponies by PAF and ADP

Altered platelet responsiveness has been demonstrated in human atopic dermatitis. This study has compared the in vitro function of platelets from normal ponies and those with the allergic skin disease, sweet itch. Ponies with a clinical history of sweet itch and normal ponies were used as blood donors. PAF and ADP-induced platelet aggregation was measured and TxB2 production quantitated at the time of maximal aggregation; 12-HETE was additionally measured in some samples. Agonist-induced release of 3[H]5-HT was also studied. Although both PAF and ADP caused equine platelet aggregation, only PAF stimulated eicosanoid and 5-HT release. There were no differences between the responses of platelets from allergic and normal ponies to PAF or ADP (analysis of variance). There is no evidence of altered platelet responsiveness in ponies with sweet itch. The profile of responses to PAF and ADP suggest differential activation of intracellular signalling pathways in equine platelets.