Etiologia e epidemiologia da dermatite alérgica sazonal em ovinos no sul do Rio Grande do Sul

Abstract

A seasonal dermatitis was studied in a Hampshire Down flock in a farm at the minicipality of Capão do Leão, state of Rio Grande do Sul, southern Brazil. Frequency and seasonal distribution of the disease, breed, sex and age of affected sheep, and clinical signs, macroscopic pathology and distribution of the lesions were obtained by visiting the farm. Histological lesions were studied in skin biopsies of affected sheep. Biting insects were collected weekly between 4:00 p.m. to 9:00 a.m., from January to April of 2005 to identify the etiological agent of disease. Data about temperature, humidity and wind speed in the region where the disease occurs were obtained in the agro climatologic Station of Pelotas Federal University. The prevalence of disease during the study period was 40% and the age of affected animals was variable. The disease occurs between December and March, but some animals stayed with lesions during the whole year. Clinical signs were characterized by pruritus and skin lesions in the ears, around the eyes, and ventral abdomen. Erythema and papules were observed in acute cases. In chronic cases, the skin was thicken, exsudative, crusty and alopecic, frequently with secondary infections. Histological lesions of affected sheep were characterized by perivascular eosinofilic dermatitis. Hyperkeratosis, acanthosis and intraepidermal pustules were observed in chronic lesions. Anopheles albitarsis and Culicoides insignis were captured during the observation period. Sheep showed pruritus mainly during de Culicoides bites. The mean minimum and maximum temperature in the period were 17ºC e 28ºC, respectively, and the mean speed wind was 12,84km/h. Both insects were caught when they approached the sheep bait 30minutes after sunset. Intradermal tests performed with de antigens of the insect extracts showed hypersensitivity reaction to C.insignis antigens. Based on the results it was suggested that the disease occurs as a consequence of an immediate hypersensitivity caused by C. insignis bite.