Summary

In a study of the skin reactivity of horses with lesions of sweet itch, six clinically normal horses and seven affected horses were challenged intradermally with extracts of Culicoides, Stomoxys, Tabanidae and Culex species. All the affected horses and three of the normal horses responded strongly to the culicoides extract. The skin reactions in the affected horses reached their maxima within 4 h in the majority of animals. Skin reactivity to culicoides was transferred to normal horses with serum from affected animals confirming that the reaction was an immediate hypersensitivity reaction. Three of the seven affected animals gave both immediate and delayed reactions when challenged with the culicoides extract. When the dermal reactions of 12 clinically normal and 10 affected horses were compared at 20 mins and 1 h after challenge, the reactions produced by the culicoides extract were significantly (P<0.025) greater in the affected than in the normal horses. Individual horses gave strong reactions to extracts of Stomoxys, Culex and Tabanidae species, but no consistent response was evident among the affected animals. Serum from horses with sweet itch sensitised the skin of normal horses to challenge with extracts of the biting flies and the transferred antibodies remained bound to the skin of the recipient horse for 72 h or longer. Although some variation among the affected horses occurred in passive transfer experiments, the response to Culicoides species extracts was consistently greater than for the other insect extracts tested.



Resume

Pour etudier la reactivite cutanee des chevaux atteint de dermite estivale recidivante, six chevaux normaux et sept malades furent intradermo inocules avec des extraits de Culicoides, de Stomoxys, de Tabanides et de Culex. Tous les chevaux malades et trois des chevaux normaux reagirent fortement a l'extrait de culicoides. Les reactions cutanees maximales furent atteints en moins de 4 heures chez la plupart des chevaux malades. La sensibilite cutanee aux culicoides fut conferee aux chevaux sains par l'administration de serum de chevaux malades. Cela confirmait l'existence d'une reaction immediate d'hypersensibilite.



Trois des sept chevaux malades presenterent deux reactions aux extraits de culicoides, l'une immediate et l'autre differee. Lorsqu'on compara les reactions dermiques de 12 chevaux normaux et de 10 chevaux malades, 20 minutes, puis 1 heure apres l'injection declenchante, on observa que les reactions produites par l'extrait de culocoides etaient plus importantes de maniere significative (P<0.025) chez les chevaux malades.



Certains chevaux eurent des reactions individuelles marquees aux extraits de Stomoxys, Culex et Tabanides, sans qu'aucune reaction ne puisse etre consideree comme interpretable. Le serum preleve sur des chevaux atteints de dermite estivale sensibilise — rait la peau des chevaux normaux a l'injection d'extraits de mouches piqueuses; les anticorps ainsi transferes restaient presents dans la peau des receveurs 72 heures et plus. A quelques variations pres constatees durant ces experiences d'immunosite passive conferee, on constatait une reponse immunitaire plus forte avec les extraits de Culicoides qu'avec les extraits provenant des autres especes utilisees.



Zusammenfassung

Anlasslich einer Untersuchung der Hautempfindlichkeit von Pferden mit Sommerekzemlasionen (“Sweet Itch”) wurden sechs klinisch gesunde und sieben erkrankte Pferde provoziert mit Extrakten von Culicoides, Stomoxys, Tabaniden und Culex sp. Alle kranken und drei normale Pferde reagierten stark auf Culicoidesextrakt. Die Hautreaktionen der erkrankten Tiere erreichten ihr Maximum innert vier Stunden bei der Mehrheit der Pferde. Die Hautreaktivitat gegen Culicoides konnte mit Serum kranker Pferde auf normale ubertragen werden, ein Beweis, dass es sich um eine Sofortreaktion handelt.



Drei der sieben erkrankten Pferde wiesen sowohl Sofortreaktionen wie auch verzogerte Reaktionen gegen Culicoidesextrakt auf.



Die Hautreaktionen von 12 klinisch gesunden und 10 erkrankten Pferde wurden 20 Minuten und 1 Stunde nach der Exposition verglichen; die Reaktionen gegen Culicoidesextrakt erwiesen sich bei affizierten Tieren als signifikant starker (p<0.025) als bei normalen Pferden.



Einzeltiere reagierten heftig gegen Stomoxys-, Culex- und Tabanidenextrakte, aber es liess sich keine konsistente Antwort herauslesen. Serum von Pferden mit Sommerekzem vermochte die Haut normaler Pferde gegen Extrakte von Stechfliegen zu sensibilisieren und die ubertragenen Antikorper blieben wahrend 72 Stunden oder langer in der Haut nachweisbar. Obgleich eine gewisse Variation unter den erkrankten Pferden in diesen passiven Uebertragungsversuchen festzustellen war, ubertraf die Reaktion gegen Culicoidesextrakt immer diejenige gegen andere Insektenextrakte.

Sweet itch: responses of clinically normal and affected horses to intradermal challenge with extracts of biting insects.

Cutaneous reactions to mosquito bites are usually pruritic weals and delayed papules. Arthus-type local and systemic symptoms can also occur but anaphylactic reactions are very rare. Both clinical and experimental evidence suggest that the various bite reactions result from sensitization to the mosquito saliva injected into the skin during feeding. Recent immunoblot studies have shown both IgG- and IgE-class anti-mosquito antibodies, but their species-specificity and clinical importance is at present unknown. In addition to an Arthus-type mechanism, both cutaneous late-phase reactivity and cell-mediated immunity may be involved in the pathophysiology of delayed mosquito-bite lesions. Cutaneous sensitization to mosquito bites can be divided into five different stages ranging from the stages of immediate wealing and delayed bite papules, to the stage of non-reactivity. No desensitization treatment is generally available for mosquito allergy but it has recently been shown that cetirizine, a potent non-sedating antihistamine, is effective against the wealing and pruritus caused by mosquito bites.

Immunology and treatment of mosquito bites

Background Commercial extracts are available for the diagnosis and treatment of mosquito allergy, but their antigen content has never been analyzed. Objective We wanted to analyze commercially available mosquito extracts and to compare these extracts with different laboratory preparations. Methods Seven commercially available mosquito whole body extracts from six companies and four laboratory mosquito preparations including saliva extract were studied. Epicutaneous tests and measurement of protein concentration were performed. Protein components were identified by sodium sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and silver stain. IgE and IgG binding antigens were analyzed by SDS-PAGE and immunoblotting with sera from mosquito-allergic subjects. Results The seven commercial materials produced wheals and papules ranging from 0 to 36 mm 2 . Their protein concentrations varied from 0.1 to 4.9 mg/mL. There were significant differences in their protein and antigen components. Some extracts contained multiple highly immunoreactive proteins and IgE- and IgG-binding antigens that are not present in mosquito saliva, but few actual salivary antigens. In the four laboratory preparations, rank ordered from whole body, head and thorax, salivary gland to saliva extracts, the amount of salivary antigens significantly increased, while non-salivary proteins and antigens significantly decreased. Conclusions Commercial mosquito extracts should be standardized. Purer mosquito extracts should be used in diagnosis and immunotherapy of mosquito allergy.

Comparison of proteins, IgE, and IgG binding antigens, and skin reactivity in commercial and laboratory-made mosquito extracts

To investigate the mechanisms responsible for mosquito bite reaction, 120 subjects were experimentally exposed to Aedes albopictus bite and two types of immunological tests were performed. Specific IgE antibodies to salivary gland extract (SGE) antigens of female Aedes albopictus were measured by enzyme-linked immunosorbent assay (ELISA) in all subjects. Lymphocyte transformation tests (LTTs) to the same antigens were measured in 51 of the 120 subjects. The relationships between the results of ELISA and LTTs with bite reactions were statistically analysed. The amount of specific IgE antibodies correlated well with immediate bite reactions (r = 0.55) (p less than 0.01). Stimulation indices (SIs) to SGE antigens correlated with delayed bite reactions (r = 0.54) (p less than 0.01). The results suggest that type I hypersensitivity plays a role in the immediate reaction to mosquito bites and a cellular immune mechanism is responsible for the pathogenesis of delayed bite reactions.

Correlation of Aedes albopictus bite reaction with IgE antibody assay and lymphocyte transformation test to mosquito salivary antigens.

Serum was collected from individuals with little, average, or extensive exposure to mosquito bites for determination of the presence of circulating antibodies to mosquito salivary gland proteins. Intensity of exposure was determined by mosquito-bite and exposure history. Sections cut through the thorax of four different species of mosquitoes, locally prevalent in South Florida, were exposed to serum and developed for antibody binding with the use of the avidin-biotin-peroxidase immunohistochemical technique. In subjects with histories of little or average exposure to mosquitoes, binding was observed that appeared to be species-specific; in subjects with extensive exposures, little antibody binding to salivary gland was noted. We hypothesize that suppression of the humoral immune response is an adaptive mechanism in response to significant exposures of mosquito salivary gland antigens.

Circulating antibody detection in human serum to mosquito salivary gland proteins by the avidin-biotin-peroxidase technique

Studies on Culex pipiens molestus in Israel

Studies on Culex pipiens molestus in Israel. I. Clinical observations on the bite reaction in man.

Studies on Culex pipiens molestus in Israel. 2. Skin response in man to extracts from the mosquito.

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Studies on Culex pipiens molestus in Israel

Studies on Culex pipiens molestus in Israel. I. Clinical observations on the bite reaction in man.

Studies on Culex pipiens molestus in Israel. 2. Skin response in man to extracts from the mosquito.