Use of nasal swabs

respiratory disease SIR, – Ruminant respiratory disease remains an important issue for veterinary practitioners, and improvement of the diagnosis can be helpful. Sheehan and others (2005) recently evaluated a transtracheal lavage technique for this purpose in sheep flocks. They concluded ‘that the culture of samples from the lower respiratory tract may be more diagnosti-cally useful than culturing nasal swabs’. It is my opinion that the authors might have disregarded that the examined nasal swabs were more frequently positive in the affected flock than the lung samples for both Mannheimia haemolytica (53·3 per cent v 13·3 per cent) and Mycoplasma ovipneumoniae (26·6 per cent v 20·0 per cent). This suggests a higher success rate of nasal swabs in diagnosing cases of res-piratory disease. The problem results from the presence of ‘pathogens ’ in clinically healthy animals. Before deciding against using nasopharyngeal samples, one must recon-sider the opportunistic pathogenic nature of the organisms causing respiratory dis-ease. If not initially involved, there is a high chance they will eventually damage the lower respiratory tract or even get transmitted to other animals. Based on the conclusion made by Sheehan and colleagues, practitioners may form the impression that nasal cul-tures are of little value for the bacterio-logical diagnosis of respiratory disease in ruminants. It is my impression that this ‘dogma ’ is widespread among veterinari-ans, partly based on two older investiga-tions dealing with calves. The first of these pioneer studies (Allan and others 1985) found no good correlation between disk diffusion susceptibility profiles o