Prevalence of Salmonella enterica subsp. diarizonae serotype 61:k:1:5:(7) in nasal secretions and stool of sheep flocks with and without cases of chronic proliferative rhinitis

Salmonella enterica subsp. diarizonae serotype 61: k: 1,5, (7) (SED) is a microorganism well adapted to sheep; however, it has also been described producing chronic proliferative rhinitis (CPR) in ovine. CPR causes a proliferative inflammation of the ventral nasal turbinates that may totally obstruct the nasal cavity. The main objective of the present study was to investigate the prevalence of SED in nostrils and stool of sheep without CPR clinical signs in commercial sheep farms of Spain with and without previous clinical cases of CPR. Five samplings were performed in 10 commercial sheep farms for one year. Samples from nostrils and faeces were taken from four animals without CPR visible clinical signs that belonged to four different age ranges at each farm visit. The prevalence of positive animals was 45.3 %, and the number of positive samples in nostrils was higher than in faeces (38.5 % vs 22.5 %). Only on one farm was no positive result obtained in the entire study. In almost all positive farms, sheep belonging to the youngest age ranges accounted for more than 50 % of positive isolates. Finally, farms with a previous diagnosis of CPR were 1.784 times more likely to have an animal with positive isolation than farms without a previous diagnosis. This could suggest that the infection pressure in the farm might favour the occurrence of clinical cases of the disease. However, further studies will be necessary to unravel why this saprophytic bacterium is able to cross the epithelial barrier causing severe rhinitis in certain animals.