Differential diagnosis of oral lesions and FMD in sheep

THE clinical examination of sheep was among the many practical problems encountered during the 2001 pan‐Asiatic type O foot‐and‐mouth disease (FMD) outbreak in the UK and was a cause for concern for many veterinary surgeons. The difficulty in diagnosing FMD arises from the fact that, often, only mild disease is seen in sheep and also because lesions associated with some of the common endemic diseases of sheep, such as interdigital dermatitis and orf (parapoxvirus infection), are similar in appearance. Oral lesions due to FMD are most likely to develop at sites vulnerable to trauma (eg, the dental pad, upper and lower gums, and the tongue). However, it became apparent during the 2001 outbreak that the differential diagnosis of FMD was further complicated by the presence of oral lesions of unknown cause (colloquially known as OMAGOD). These lesions can be quite common and subsequent studies have confirmed that trauma alone is the primary cause. This article discusses the causes of oral ulceration and how these lesions might be differentiated from those due to FMD. The differential diagnosis of endemic foot diseases, which can appear very similar to FMD, is not covered. Other oral abnormalities, such as dental disease or neoplasia, are not relevant to the differential diagnosis of FMD and, hence, are also not considered here.