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WE wish to report details of recent outbreaks of interstitial pneumonia (IP), mainly in calves, which have illustrated the difficulties associated with achieving a diagnosis. The principal features in IP are diffuse pathology affecting the whole lung field and histopathological evidence of inflammatory damage primarily involving the alveolar or interlobular septae, these being referred to as the ‘lung interstitium’ (Coswell and Williams 2007). Diffuse emphysema and oedema are usually present.
‘Fog fever’ is a form of IP which occurs in suckler cows after moving to lush pasture, usually occurring in late summer or autumn (Selman and others 1974). Several other specific inciting causes of IP have been identified. It can be a feature of some forms of ‘husk’ associated with infection by Dictyocaulus viviparus, and may be seen with respiratory syncytial virus (RSV) infections. The inhalation of silo gas or ingestion of toxic agents, including purple mint (Perilla frutescens) and various brassicas (Woolums and others 2001, Kerr and Linnabary 1988) has also been reported. An outbreak of IP in East Anglia, which was investigated by APHA Bury St Edmunds Veterinary Investigation Centre (VIC), was associated with the feeding of mouldy sweet potatoes (Mawhinney and others 2008), similar outbreaks having previously been recognised in the USA. Unfortunately the specific cause of some outbreaks of IP cannot be identified, and in such cases there is potential for further disease to occur.
Whatever the inciting cause of an outbreak of IP, a common metabolic pathway is considered to occur (Loneragan and others 2001); there …