A small herd of 16 adults and 2 calves near Narrabri developed intense pruritis in association with nodular skin lesions mainly in the region of the neck, perineum and upper caudal surfaces of the hind legs. Chorioptic mange is a pruritic skin disease of cattle characteristically involving small nodules that exude serum, progressing to form crusts and scabs.
It is caused by the mite Chorioptes bovis and usually begins on the legs, spreading to the scrotum, tail and perineal area. The nodules seen in this case were raised from the surrounding skin and ranged in diameter from 5mm to 20mm. They did not show the characteristic scabbing, but did exhibit damage attributable to traumatic injury associated with pruritis. Skin lesions attributable to Chorioptes bovis are usually less well circumscribed than those seen in this case.
The exotic Lumpy Skin Disease (caused by a capripoxvirus) and Pseudo Lumpy Skin Disease (caused by bovine herpesvirus 2) were considered as differentials due to the nature of the nodules and distribution, however they were deemed less probable as the cattle were not showing signs of systemic illness. Also, pruritis is not generally a feature of either condition.
Clinical examination of individuals and skin scrapings were not undertaken due to inadequate facilities, so treatment with a macrocyclic lactone pour-on was suggested. The cattle ceased rubbing within 2-3 days of treatment and the owner reported that the nodules had disappeared within a week. Response to therapy suggests that Chorioptes bovis was the causative organism.