Pelodera dermatitis in sheep

Abstract

were removed twice a year, in spring and autumn, and produced a high level of humidity especially in areas close to the drinking places. The disease was seasonal with the problem occurring between December and April in each of the three consecutive years. The body areas affected were those in contact with the floor or bedding when the animals were lying down. Feeding was based on a mixture of cereals, granulated alfalfa and hay, and no variation of the ingredients occurred during the year. Lambs born from affected sheep did not develop the skin disease and were raised normally by their mothers. Affected animals were calm and the only apparent sign of pruritus was erythema. Clinical parameters were normal and no abnormalities of the organs were found. Detailed clinical examination revealed large areas of lichenified, exfoliating skin with hyperhydrosis at the edges of the lesions. There was loss of wool from the ventral abdomen and thorax and from the extremities (Fig 1). Animals could be divided into three groups according to the distribution and type of lesions. Out of the 58 animals present during the final winter 15 were free of lesions, 21 had lesions on the ventral thorax, eight had lesions of the axilla, thorax and ventral abdomen, and 14 showed lesions on all the ventral areas of the body and also on the lateral aspects of the hindlegs. Some animals of this last group also had lesions of the tail and perineal region and wool around these areas was easily epilated. Seventy-four per cent of animals were affected, but in no case was there involvement of the head or dorsal trunk. Skin scrapings, skin biopsies, blood and faecal samples and samples of bedding were taken. The skin scrapings were negative, as were bacterial and fungal cultures. No parasites were observed. Total and differential blood cell counts, packed cell volume and haemoglobin concentration were all normal, as were serum levels of copper and zinc. Total proteins and protein fractions were analysed and no abnormalities found. Histopathology was performed on biopsies from a number of sheep. All the biopsies contained a perivascular dermatitis characterised by eosinophils and mast cells in loose connective tissue. Some lymphocytes and plasma cells were present. In addition there was a severe perifolliculitis and folliculitis with accumulations of neutrophils, lymphocytes and plasma cells. In each case, both superficially and deeply within the hair follicles, fragments of parasites consistent with Pelodera species in transverse and oblique section were found (Figs 2 and 3). Some organisms were also found outside the hair follicle and within the dermis. The inflammatory infiltrate also affected the sebaceous and sweat glands, but to a lesser degree, and the sweat glands were dilated. The epidermis showed hyperkeratosis and slight acanthosis into the hair follicles. In the faeces no eggs of Bunostomun trigonocephalum, Strongyloides papillosus or any other parasite were found. In contrast, large numbers of larvae of the nematode P strongyloides were found in the bedding samples. FIG 1: Loss of wool and areas of lichenified, exfoliating skin on the ventral abdomen and thorax